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QM455 .W58 The anatomy of the b 

The Anatomy 



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Open Knowledge Commons 


r r.i IT' c \ I (II ,\'ri C IS \ 


Anatomy of the Brain 


Richard H. Whitehead, IM.E). 


Tllttstratea with forty-one engravings 








[Registered at Stationers' Hall, London, Eng. 

Philadelphia, Pa., U. S. A. : 

The Medical Bulletin Printing-House, 

1916 Cherry Street. 


Ix the preparation of tliis little book it lias been the 
author's aim to fnrnish medical students with a clear, accu- 
rate, and concise account of the anatomy of the brain, to be 
used as a guide in their study of that organ. Erom a work 
of this character it has been thought best to omit minor de- 
tails, and to exclude, so far as seemed possible, subjects which 
are still matters of controversy. 

Kecognizing the value of a uniform nomenclature, use 
has been made of the Latin terms adopted and recommended 
by the German Anatomical Society at its meeting in Basel, 
to the extent that they have been inserted, parenthetically, 
after the names commonly employed in this country. 

UxivEKSiTY OF North Caeolina, 
April. 1899. 



The Divisions of the Encephalon 1 

The Sukface Anatomy of the Encephalon 6 

The Internal Anatomy of the Encephalon 34 


The Conducting-paths of the Encephalon 86 


. The Divisions of the Encephalox. 

As THE division of the encephalon, or brain, into its 
several parts is based upon tbe embryological development of 
that organ, it will be necessary to briefly consider the early 
development of the central nervous system. 

Fig. 1. — Transverse section of first-day chick (after Duval). 
Ep., Epiblast. N. c, Neural canal. 

The cerebro-spinal nervous system makes its first appear- 
ance as two ridges of epiblast bordering a groove in the 
median line (Figs. 1 and 2). As these ridges increase in 
elevation, they soon meet over the back of the groove, which 

Fig. 2. — Transverse section of first-day chick (after Duval). 
Reference letters as in Fi^. 1. 

thus becomes a canal: the neural canal. At this period the 
embryonic nervous Vystem may be represented as a cylinder 
whose walls are formed by epithelial cells; in this stage it 
is called the neural axis. While the great majority of the 
cells become differentiated into neurones and their supporting 



tissue, — the neuroglia, — some remain as a lining to tlie canal, 
forming the ependymal epithelium. The neural canal per- 
sists throughout life under different names, and varies much 
in size in different portions of the nervous system. 

That part of the neural axis which is contained within 
the embryonic cranium and which is to become the brain is 
seen, at a very early stage, to be dilated into three sacs, or 
vesicles, known from behind forward as the rhombencephalon, 
mesencephalon, and prosencephalon. A little later the first 
and third of these vesicles are differentiated into two each, 
the rhombencephalon becoming divided into the myelenceph- 
alon and metencephalon, while the prosencephalon gives rise 
to the diencephalon and the telencephalon. Thus, there are 
now five vesicles from behind forward: the myelencephalon, 
the metencephalon, the mesencephalon, the diencephalon, and 
the telencephalon (Fig. 3). 

From these five vesicles are developed all the parts of 
the encephalon which we are about to study. Moreover, since 
the five primary divisions maintain their individuality more 
or less distinctly in the fully developed brain, those parts of 
it which a given vesicle produces are called collectively by 
the same name as the parent-vesicle. In other words, the 
vesicle bears the same name both in the undeveloped and in 
the mature state. 

The encephalon is divided into five parts, then, as fol- 
lows (Figs. 3, 4, and 5): — 

1. The myelencephalon, or the medulla oblongata. 

2. The metencephalon, composed of the pons Varolii 
and the cerebellum. The pons Varolii is developed from that 
portion of the metencephalon which lies ventral to the neural 
canal, the part which lies dorsal to the canal producing the 
cerebellum. The most anterior portion of the metencephalon 
may be individualized into a separate division under the name 
of the isthmus of the rhombencephalon. The neural canal 
in the region of the rhombencephalon becomes the fourth 

3. The mesencephalon, consisting of the corpora quad- 
rigemina dorsal to, and the peduncles of the cerebrum ven- 


Fig. 3. — Sagittal section of brain of one-month human embryo (after 
His). /. Myelencephalon : /.I, Ventral portion; 1.2, dorsal portion. 
//. Meteneephalon: 7/.1, Pons Varolii; II. 2, cerebellum. ///. Isthmus 
rhombencephali : 777.1, Ventral portion; 777.2, dorsal portion. lY. Mesen- 
cephalon: 7y.l, Pedunculi cerebri; 77.2, corpora quadrigemina. Y. Dien- 
cephalon: F.l, Pars mamillaris hypothalami; Y.2, thalamus; F.3, meta- 
thalamus; 7.4, epithalamus. 77. Telencephalon: 77.1, Pars optica hypo- 
thalami; 77.2, corpus striatum; 77.3, rhinencephalon; 77.4, pallium. 


tral to, the neural canal, which here is called the aqueduct of 

4. The diencephalon. This is divided into the thala- 
niencephalon dorsal to, and the hypothalamus ventral to, the 
neural canal. The thalamencephalon is subdivided on each 
side of the median line into the thalamus, the epithalamus 
(or the pineal body and habenula), and the metathalamus (or 
the geniculate bodies). The neural canal in this situation is 
called the third ventricle. Ventral to it is the hypothalamus, 
only the posterior part of which, however, belongs to the 

5. The telencephalon. This consists of the hemispheres 
dorsal to the neural canal, while a small ventral portion forms 
the anterior part of the hypothalamus. Here the neural canal 
develops into the lateral ventricles. As the result of very rapid 
growth, especially in its lateral portions, the telencephalon 
soon outgrows its neighbors, and overlaps the diencephalon 
and mesencephalon. To these three divisions — telencepha- 
lon, diencephalon, and mesencephalon — collectively the term 
cerebrum is commonly applied. 


Fig. 4. — Sagittal section of brain of mammal (after Edinger). 
Keference numbers as in Fig. 3. 

Fig. 5. — Sagittal section of human brain (after His). 
Eeference numbers as in Fig. 3. 


The Surface A^'ATOMY of tiie Excephalox. 


The myelenceplialon or tlie medulla oblongata extends 
between the spinal cord behind and the pons Varolii in front. 
It is somewhat conical in shape, with its base forward and 
on a plane dorsal to the smaller extremity, which is contin- 
uous with the spinal cord. It is about one and one-quarter 
inches long, and its widest diameter measures nearly one inch. 
It rests upon the posterior part of the concave surface of the 
basilar process of the occiput. For purposes of description it 
may be divided into a ventral surface, a dorsal surface, and 
two lateral surfaces. 

The ventral surface (Eig. 6) presents in the median line 
a well-marked longitudinal groove, — the ventral median fis- 
sure (fissura mediana anterior), — on each side of which is a 
rounded band, the pyramid fpyramis). Xear the spinal cord 
the fissure is almost obliterated by fibres which pass' across from 
one p;sTamid into the other; this is called the decussation of 
the pyramids (decussatio pyramidum). Lateral to each pyra- 
mid and separating the ventral from the lateral surface is the 
ventro-lateral sulcus (sulcus lateralis anterior), from which 
emerge the root-fibres of the twelfth cranial, or' hypoglossal, 
nerve (nervus hypoglossus). 

The lateral surface (Eig. 6) in its posterior half is known 
as the lateral tract (funiculus lateralis). Its anterior half is 
occupied by an oval mass called the olive (oliva). Each 
lateral is separated from the dorsal surface of the medulla 
by the dorso-lateral sulcus (sulcus lateralis posterior), from 
which many nerve-fibres escape to soon unite and' form three 
nerves; from before backward these are the ninth (nervus 
glosso-pharyngeus), the tenth (nervus vagus), and the acces- 
sory portion of the eleventh (nervus accessorius) cranial nerves. 
It will be noticed that the posterior part of this sulcus is in- 






Sabs int 


Fig. 6. — Roman numerals refer to cranial nerves. C'.l, First cervical 
spinal nerve. C. mam., Corpus mamillare. Op. n., Optic nerve. Inf., In- 
fundibulum. Op. ch., Optic chiasm. Siibs. int., Substantia interpeduncu- 
laris. Op. tr., Optic tract. P. C, Peduncle of cerebrum. G. g. I., Lateral 
geniculate body. Sul. 6., Basilar sulcus. M. p. c, Middle peduncle of cere- 
bellum. F., Flocculus. F. h., Horizontal fissure. 0., Olive. T. I. s., Ventro- 
lateral sulcus. Pijr., Pyramid. T. m. f.. Ventral median fissure. (After 
Van Gehuchten. ) 


terrupted'by the passing of a part of the lateral tract to the 
dorsal surface of the medulla. 

The ventral and lateral surfaces of the medulla are clearly 
limited from the pons Varolii by a transverse groove. In this 
groove appear the root-fibres of three cranial nerves: the 
sixth (nervus abducens), opposite the pyramid; the seventh 
(nervus facialis), opposite the dorso-lateral sulcus; and the 
eighth (nervus acusticus), still farther lateral. 

The dorsal surface (Fig. 7) may be divided into an ante- 
rior and a posterior half. The latter resembles the spinal 
cord; here we find in the median line the dorsal median 
fissure (fissura mediana posterior), and on each side of it the 
continuation of the dorsal funiculi of the cord, — the funiculus 
of Goll (funiculus gracilis), next to the median fissure and 
separated laterally from the funiculus of Burdach (funiculus 
cuneatus) by the paramedian fissure. These two funiculi 
terminate forward, the former in a small elevation called the 
clava, the latter in a less distinct elevation extending farther 
forward called the cuneate tubercle. 

Owing to the termination of these dorsal funiculi and 
to an increase in the transverse diameter of the neural canal 
at this point, the anterior division of the dorsal surface pre- 
sents a depression, which is bounded laterally by a white cord : 
the corpus restiforme. The two corpora restiformia diverge 
to enter the cerebellum, leaving thus between them a tri- 
angular depression, which is the floor of the neural canal, 
and is called the calamus scriptorius. As it is also the poste- 
rior (inferior) part of the floor (fossa rhomboidea) of the 
fou.rth ventricle, which is the neural canal of the rhomben- 
cephalon, it is called the pars inferior fossse rhomboidese. 
The base of the triangular depression is forward, and nearly 
corresponds to some fibres seen crossing the fioor of the ven- 
tricle on each side: the striae acusticse (striae inedullares). 
These emerge from the longitudinal median sulcus, which is 
continuous, not with the dorsal median fissure of the medulla, 
but with the floor of the central canal continued from the 
cord into the medulla. Between this sulcus and the corpus 
restiforme the dorsal surface on each side may be divided 
into three triangles, as follows: Bordering the sulcus- is a 


Nuc. Cmid, 



. Nuc.caud. 

ThaL^ _.-^' 


- -K 


^^ -I " - 


' F^ 

'-'"'' \i 

' - Lat.lem. 
. A.p.c. 

^^ .3ta. 

-:-:-- M.p.c. 

Al.cin.- - 



CL - - 

\a:\ . 



_ _!-- 




- --- 





Fig. 7. — Sul. ch., Choiioid sulcus. Nuc. caud., Nucleus caudatus. Thai., 
Thalamus. St. m., Stria medullaris. P. b., Pineal body. G. q., Corpora 
quadrigemina. P^ilv., Pulvinar. Fr., Frenulum. Lat. lem., Medial lemniscus. 
A. p. c, Anterior peduncle of cerebellum. M. p. c, Middle peduncle of cere- 
bellum. St. a., Acoustic striae. C. r., Corpus restiforme. G. tub., Cuneate 
tubercle. F. O., Funiculus of Goll. D. m. f., Dorsal median fissure. P. sul, 
Paramedian sulcus. L. tr., Lateral tract. D. I. sul., Dorso-lateral sulcus. 
F. B., Funiculus of Burdach. CI., Clava. Al. cin., Ala cinerea. T. h., Hypo- 
glossal triangle. A. a., Acoustic area. G. f., Colliculus facialis. S. Urn., 
Sulcus limitans. E. m., Eminentia medialis. Y. Y., Anterior medullary 
velum. IT, Trochlear nerve. G. g. m., Medial geniculate body. G. g. I., 
Lateral geniculate body. P. Ir., Posterior brachium of mesencephalon. 
(After Van Gehuchten.) 


small triangular area ^vitll its base forward; this is the land- 
mark of the nucleus of the twelfth cranial or hypoglossal 
nerye, and is called, therefore, the hypoglossal triangle (tri- 
gonnm neryi hypoglossi). The hypoglossal triangle is bounded 
laterally by a faint sulcus, the sulcus limitans, which sep- 
arates it from the second triangular area, which is somewhat 
darker in color, and is known as the ala cinerea; this has its 
apex forward, and is the landmark of the sensory nuclei of 
the ninth and tenth cranial nerves. The third triangle is 
found between the ala cinerea and the corpus restiforme; it 
has its base forward at the striae acusticse, and is the posterior 
portion of the acoustic area (area acustica), containing nuclei 
of the eighth cranial, or acoustic, nerve. 


The metencephalon is composed of the pons Varolii and 
the cerebellum. 

The Poxs Varolii. — This presents for study two sur- 
faces: a ventral and a dorsal. 

The ventral surface (Tig. 6) is situated between the cere- 
bral peduncles in front, the medulla oblongata behind, and 
the cerebellum laterally. It is constituted by a broad layer 
of transverse fibres, which contracts on each side, and enters 
the cerebellum as its. middle peduncle (brachium pontis). In 
the median line is an antero-posterior groove, — the • basilar 
sulcus (sulcus basilaris) for the basilar artery, — and on each 
side of this a ridge thrown up by the passage of the fibres 
which constitute the pyramid in the medulla. Laterally ap-, 
pear the root-fibres of the fifth cranial, or trigeminal, nerve 
(nervus trigeminus), piercing this surface of the pons. 

To examine the dorsal surface it is necessary to remove 
the cerebellum. It is then seen that this surface consists of 
an elevated cord on each side, with a depression between (Fig. 
7). The cords are the anterior peduncles of the cerebellum 
(brachia conjunctiva), which converge toward the mesenceph- 
alon, where they disappear. Lateral to the peduncle a band 
of fibres can be seen winding forward and dorsalward to reach 
the mesencephalon; this is the lateral lemniscus (lemniscus 




Post com. 

h pi 

^Antcom. ^' 
_'■--- -Op.r: 
~ -IvF.r- 

■^ Mas. int. 
- Of-ch. 



Fig. S.Spl., Splenium. Thai., Thalamus. St. med., Medullary stria. ^ 
Sul. hyp., Sulcus hypothalamicus. Corp. cal., Corpus eallosum. Sep. pel.. 
Septum pellucidum. G., Genu of corpus eallosum. Col. for., Column of 
fornix. C7i. pi., Chorioid plexus of lateral ventricle. L. t., Lamina terminalis. 
Ant. com., Anterior commissure. Op. r., Optic recess. Inf. r., Recess of 
infundibulum. Mas. int., Massa intermedia. Op. cli.. Optic chiasm. Tut), cin.. 
Tuber cinereum. Eyp., Hypophysis. Ill, Oculomotor nerve. C. mam.. Cor- 
pus mamillare. P. C, Peduncle of cerebrum. P., Pons Varolii. Aq. S., 
Aqueduct of Sylvius. Y. V., Anterior medullary velum. J/.. ]\Iedulla ob- 
longata. F. v., Fourth ventricle. P. v. p., Posterior vermiform process. C, 
Cerebellum. A. v. p.. Anterior vermiform process. Post, com., Posterior com- 
missure. P. b., Pineal body. C. q., Corpora quadrigemina. (After Van 


lateralis). The depression between the pednncles is triangnlar 
in shape, and forms the anterior part of the floor of the fourth 
ventricle. It is covered over by a thin, white lamina, stretch- 
ing across from one peduncle to the other, continuous in front 
with the mesencephalon, behind with the cerebellum; it is 
known as the valve of Yieussens, or anterior medullary velum 
(velum medullare anterius), and through it the fourth cranial 
nerve (nervus trochlearis) escapes on each side. , The depres; 
sion has its base backward, coinciding with that of the calamus 
scriptorius of the medulla, between which and the pons there 
is no distinct boundary on the dorsal aspect. In the median 
line is seen the forward continuation of the dorsal median 
sulcus of the medulla, and laterally the forward prolongation 
of the sulcus limitans. These two sulci inclose between them 
a ridge, the medial eminence (eminentia medialis), which is 
the landmark of the nucleus of the sixth cranial nerve. On 
each side of the median sulcus at about its middle the floor 
of the ventricle is thrown up into a small rounded eminence 
by the root-fibres of the seventh cranial nerve, called the col- 
liculus facialis. In front the sulcus limitans deepens some- 
what to form the anterior fovea (fovea superior); behind, on 
the medulla, at the apex of the ala cinerea, it, in like manner, 
forms the posterior fovea (fovea inferior). Lateral to the 
anterior fovea, at the line of junction of the floor with the 
side of the ventricle, is a bluish spot, the locus coeruleus, which 
is the landmark of the nucleus of the trigeminal nerve. In 
the angle formed by the corpus restiforme behind and the 
anterior peduncle in front, lateral to the sulcus limitans, is 
the acoustic area (area aeustica), which is situated partly on 
the pons and partly on the medulla, and is bisected by striae 

The Ceeebellu:\[. — On external examination the cere- 
bellum appears laminated, consisting of plates of nervous 
matter separated by narrow sulci. In shape it is rather oblong, 
and is about four inches wide and two inches in its dorso- 
ventral diameter. It occupies the inferior occipital fossae of 
the skull. It may be divided into an anterior, a posterior, and 
a ventral surface. The anterior surface (Fig. 8) is marked 
in the median line by an elevated portion called the anterior 



' Sulh. 

/ Tloc. 

Fig. 9. — y. «., Ventral extremity of anterior vermiform process. F. F., 
Anterior medullary velum. A. p. c, Anterior peduncle of cerebellum. 
Md. av., Nidus avis. M. j). c, Middle peduncle of cerebellum. Svl. h., Hori- 
zontal sulcus. Floe, Flocculus. C. v., Corpus restiforme. P. m. v., Posterior 
medullary velum.- Nod., Nodulus. (After Van Gehuchten.) 


(snperior) vermiform process (vermis superior), terminating 
ventrally at a notch, — the ventral incisure (incisura ante- 
rior), — and dorsally at a deeper notch, — the dorsal incisure 
(incisura posterior). On the posterior surface opposite to the 
anterior vermiform process is a deep groove, the vallecula, in 
the bottom of which is the posterior (inferior) vermiform 
process (vermis inferior). It will be noticed that the two 
vermiform processes are continuous dorsally and form one 
lobe, which is termed the worm (vermis). The worm and the 
notches form the landmarks for dividing the remainder of the 
cerebellum into two hemispheres. The cerebellum has been 
further subdivided into numerous lobes, but, as our knowledge 
of the functions of the cerebellum is so imperfect, their 
names, which are in many instances fanciful, may be here 

To examine the ventral surface, the cerebellum must be 
removed from its connections by severing its various peduncles. 
When this has been done (Fig. 9) we find in the median line 
the ventral extremity of the anterior vermiform process in 
front, and the ventral extremity of the posterior vermiform 
process, called the nodulus, behind. The former rests upon a 
thin sheet of white matter, which will be recognized as the ante- 
rior medullary velum, over which the worm sends forward a 
thiPi 'Strip : the lingula. On each side the velum is attached to 
the anterior peduncle, the cross sections of which are here seen. 
Posterior to the anterior medullary velum is the transverse 
fissure (fissura transversa), leading into a cleft, or cul-de-sac, 
called the tent, or "bird's nest" (nidus avis). Lateral to this is 
the section of the corpus restiforme, and lateral to it the larger 
section of the middle peduncle. Still farther lateral is the 
beginning of a fissure which can be traced around the circum- 
ference of the cerebellum to a corresponding point on the op- 
posite side: the horizontal fissure (fissura horizontalis). In the 
commencement of this fissure is a quite distinct lobule: the 
flocculus. From the flocculus a delicate layer of white matter 
runs toward the median line, and crosses on the anterior aspect 
of the nodulus to gain the flocculus of the opposite side ; this 
is the posterior medullary velum (velum medullare posterius). 
It is thus seen that the tent is a cleft in the white matter of 


the cerebellum between tbe two medullary vela. It is pro- 
longed on eacb side as far as tbe middle peduncle, wbicb lateral 
prolongations, as we shall hereafter see, are the lateral recesses 
of the fourth ventricle, toward which cavity this surface of the 
cerebellum looks. 


The isthmus of the rhombencephalon (isthmus rhomben- 
cephali) is the name given to the most anterior part of the 
rhombencephalon, uniting that vesicle to the mesencephalon. 
In the embryo it exists as a separate vesicle, but in the de- 
veloped brain it has no distinct boundaries. Its dorsal portion 
consists of the anterior peduncles of the cerebellum and the 
anterior medullary velum; these we have described as a part 
of the pons Varolii. Its ventral portion is furnished by the 
beginning of the cerebral peduncles, including the nuclei of 
the fourth pair of cranial nerves ; these we shall study in con- 
nection with the mesencephalon. 


The fourth ventricle (ventriculus quartus) is the neural 
canal in the rhombencephalon (Fig. 7). It may be considered 
as having a floor, a roof, and two sides. The floor (fossa rhom- 
boidea) is diamond-shaped, and is furnished by the triangular 
depression on the dorsal surface of the pons in front, and by 
the calamus scriptorius of the medulla behind. If we regard 
the isthmus of the rhombencephalon as a separate division, 
there are three contributors to the floor: the isthmus furnish- 
ing the anterior portion (pars superior) ; the pons forming the 
middle portion (pars intermedia), — the part included between 
lines embracing the middle peduncles of the cerebellum; 
while the medulla contributes the posterior portion (pars in- 
ferior fossae rhomboidese). The appearances in the floor of 
the ventricle have been already described in the accounts of 
the medulla and of the pons. 

The sides or lateral boundaries of this diamond-shaped 
space are furnished in front by the anterior peduncles of the 
cerebellum and behind by the corpora restiformia. 


The roof of the ventricle in its anterior portion is the 
anterior medullary velnm; the posterior part of the roof 
is furnished by a reflection of the pia mater known as the 
tela chorioidea. To gain a correct conception of this, part 
of the roof it will be necessary to revert, for a moment, 
to the development of the rhombencephalon. The epithe- 
lial cells forming the dorsal wall of the embryonic rhomb- 
encephalon produce the anterior medullary velum in front, 
and the worm and posterior medullary, velum of the cere- 
bellum in the middle; but, along a line corresponding to the 
free edge of the posterior medullary velum, this epithelium 
ceases to develop nervous tissue. In the mature brain, there- 
fore, the dorsal wall of the rhombencephalon reaches, in its 
primitive condition as a layer of epithelial cells, from the edge 
of the posterior medullary velum in front to the medulla be- 
hind (Fig. 4). This layer is consequently triangular, with its 
base at the edge of the velum, its apex continuous with the 
epithelium lining the dorsal wall of the central canal of the 
medulla, and its sides attached to the medial surfaces of the 
corpora restif ormia, where the production of nervous substance 
is resumed. 'Now, the pia mater, adhering closely to the en- 
cephalon at all points, enters the space between the cerebellum 
and the medulla, and invaginates this epithelial membrane, 
p ashing it ahead as far as the lateral recesses. This fold of pia 
mater is the tela chorioidea. The epithelium adheres to its 
ventricular aspect, and is therefore called the lamina chorioidea 
epithelialis. As a matter of fact, the epithelium is the j:rue 
roof of the ventricle ; but, since it is adherent to the tela, and 
is torn from its other attachments when the tela is removed, 
the latter is commonly called the roof. On its ventricular sur- 
face the tela presents a row of vascular tufts on each side of 
the median line: the median chorioid plexus (plexus chori- 
oideus ventriculi quarti). N'ear its anterior margin the plexuses 
turn and run lateralward, and in this situation are called the 
lateral chorioid plexuses. There is frequently an opening in 
the tela known as the foramen of Magendie ; so that the cavity 
of the fourth ventricle communicates with the space between 
the pia mater and the arachnoid. 

The ventricle has four angles : an anterior, where it is con- 





.,. Col. fori 




..- Tn^,hah. 
. Thai, 


Fig. 10. — A. c, Anterior horn of lateral ventricle. H. ntic. caud., Head 
of caudate nucleus. Col. for., Column of fornix. F. M., Foramen of Monro. 
A. t. thai., Anterior tubercle of thalamus. St. term.. Stria terminalis. Nuc. 
caud., Nucleus caudatus. Yen. Ill, Third ventricle. Trig. Ml)., Trigonum 
habenulae. Thai., Thalamus. Siil. ch., Chorioidal sulcus. T. nuc. caud., 
Tail of nucleus caudatus. Pulv., Pulvinar. Teg., Tegmentum. T. T., An- 
terior medullary velum. G. q., Corpora quadrigemina. Hab., Habenula. 
P. h.. Pineal body. Med. St., Medullary stria. Has. int., Massa intermedia. 
Sep. pel.. Septum pellucidum. A. p. c, Anterior peduncle of cerebellum. 
(After Van Gehuchten.) 


tinuoiis .with, tile aqueduct of Sylvius ; a posterior, where it is 
continuous with the canal of the medulla between the two 
clavse; and two lateral. The latter are the angular intervals 
between the diverging corpora restiformia and the anterior 
jjeduncles of the cerebellum. As we have seen, these are the 
lateral prolongations of the tent of the cerebellum, and each 
is here called a lateral recess (recessus lateralis) of the ventricle. 


The mesencephalon has four surfaces : a dorsal, a ventral, 
and two lateral. The dorsal surface (Figs. 1 and 10), which, 
in the complete encephalon, lies just ventral to the posterior 
extremity of the corpus callosum and anterior to the ventral 
incisure of the cerebellum, consists of two pairs of rounded 
bodies known collectively as the corpora quadrigemina, each 
body individually being called a colliculus. The two posterior 
(inferior) colliculi (colliculi inferiores) are the smaller, and 
are on a plane ventral as well as posterior to the anterior 
(superior) colliculi (colliculi superiores). These four bodies 
are separated from each other by a crucial sulcus ; the longi- 
tudinal arm of this groove terminates behind on the anterior 
medullary velum, its edges here forming the frenulum veli. 
J^iach colliculus has running forward and lateralward from it a 
ridge connecting the mesencephalon with the diencephalon ; 
the ridge from the anterior colliculus is called the anterior 
(superior) arm (braehium quadrigeminum superius), and that 
from the posterior colliculus is the posterior (inferior) arm 
(braehium quadrigeminum inferius). The brachia are sepa- 
rated by an interbrachial sulcus (sulcus interbrachialis). . 

The ventral surface (Fig. 6) presents two large rounded 
cords emerging from the pons Varolii : the cerebral peduncles 
(pedunculi cerebri). These diverge from each other to dis- 
.appear under the diencephalon after a course of about half 
an inch. The triangular depression left between them is the 
interpeduncular fossa (fossa interpeduncularis), in the bottom 
of which is a thin lamella of nervous tissue containing many 
foramina: the posterior perforated substance (substantia per- 
forata posterior). The foramina are produced by blood-vessels, 


wliicli pierce the lamella and are pulled out wlien the pia mater 
is removed. Through the fossa the third pair of cranial nerves 
makes its escape from the mesencephalon. 

The lateral surface is marked by a longitudinal sulcus, — 
the sulcus lateralis, — which indicates the separation of the 
quadrigeminal from the peduncular portion of the mesen- 

The cavity of the mesencephalon is the aqueduct of Syl- 
vius (aquaeductus cerebri), opening behind into the fourth, and 
in front into the third ventricle. 


The diencephalon is divided into the thalamencephalon 
and the hypothalamus. The neural canal here is the third 

The Thalamexcephalox. — The thalamencephalon (Fig. 
10) is subdivided on each side of the median line into the thala- 
mus, the metathalamus, and the epithalamus. 

Tlie Thalamus. — This is an elongated oval mass of gray 
matter having four surfaces: dorsal, ventral, lateral, and 
medial; and two extremities: anterior and posterior. 

The dorsal surface is marked by an obliquely lateral an- 
tero-posterior groove, the chorioid sulcus, in which lies, as we 
shall see hereafter, the chorioid plexus of the lateral ventricle. 
At its line of junction with the medial surface is a narrow 
white band, — the stria medullaris, — which can be traced back- 
ward to a small triangular swelling: the trigonum habenulse. 
Laterally the dorsal surface is separated from another gray 
mass, — the caudate nucleus of the corpus striatum of the telen- 
cephalon, — by a groove which lodges a vein, — the vena ter- 
minalis, — and a small bundle of fibres : the stria terminalis. 

The medial surface (Fig. 8) forms the lateral wall of the 
third ventricle. It is marked by an antero-posterior sulcus, — 
the sulcus of Monro (sulcus hypothalamicus), — which indi- 
cates the division of the thalamus from the hypothalamus. 
The lateral surface of the thalamus is fused with the telen- 
cephalon ; the ventral surface with the hypothalamus and with 
the mesencephalon behind. The anterior extremity of the 


THE axato:mt of the braix. 

thalamus is tlie smaller; its most prominent portion is called 
tlie anterior tubercle (tubercnlum anterius). 

The posterior extremity projects backward, and lateral- 
ward so as to overhang the neighboring part of the mesen- 
cephalon; this projecting portion is called the pulvinar. On 
its ventral aspect the posterior extremity is continuous with 
a white cord, — the optic tract (tractus opticus), — ^which can 
be traced winding forward, first lateral and then ventral to the 
cerebral peduncle, and then medialward into the postero-lateral 
angle of a square white body, — the optic chiasm (chiasma op- 

Fig. 11. — A. p. c, Anterior peduncle of the cerebellum. C. g.. m., Corpus 
geniculatum mediale. C. g. L., Corpus genieulatum laterale. B. F., Base 
of the peduncle of the cerebrum. Op. tr., Optic tract. Op. cJi., Optic diiasm. 
PuJv., Pulvinar of the thalamus. (After Gegenbauer.) 

ticum), — from the antero-lateral angle of which another white 
cord — the optic nerve — ^proceeds forward and lateralward. 

The Jletathcdamus. — The metathalamus (Fig. 11) con- 
sists of the two geniculate bodies, lateral and medial (corpus 
geniculatum laterale; corpus geniculatum mediale). -These 
are two small oval bodies which lie ventral to the posterior 
extremity of the thalamus. The corpus geniculatum laterale 
is situated on the course of the optic tract, and is connected 
with the anterior arm (brachium quadrigeminum superius) of 


tlie mesenceplialon; the corpus genicuktmn mediale is found 
at the lateral end of the interbrachial sulcus, and is connected 
with the posterior arm (brachium quadrigeminum inferius). 

TheEpithalamus. — The epithalamus (Fig. 10) comprises 
the pineal body (corpus pineale) and the region of the haben- 
ula. The pineal body is a small flattened oval mass somewhat 
reddish in color, and about one-quarter of an inch in diameter; 
it rests in the median line on the anterior (superior) collicuH 
of the mesencephalon. From its anterior aspect there runs on 
each side a slender cord, the peduncle of the pineal body, 
forward to the habenula. To the unaided eye the peduncle 
of the pineal body and the habenula seem to be one and the 
same structure, mth the trigonum as a swelling on it ; but, as 
it is known that the peduncles connect the trigonum of one 
side with that of the other side, they are called the commissure 
of the habenulse (commissura habenularum). 

The Thied Yextricle. — The third ventricle (ventriculus 
tertius) is the neural canal in the diencephalon, which exists 
here as a narrow space between the medial surfaces of the two 
thalami, the latter constituting its lateral walls. Its anterior 
boundary is furnished by the anterior pillars of the fornix and 
by the anterior commissure of the cerebrum. These struct- 
ures are parts of the telencephalon, and will be described in 
the appropriate place. The pillars of the fornix show here as 
two white cords running toward the ventral surface of the 
encephalon; they diverge in their course and allow the an- 
terior commissure in front of them to come into view. The 
posterior boundary is a transverse bundle of fibres: the pos- 
terior commissure (commissura posterior). Passing between 
the adjacent surfaces of the thalami about the middle of the 
ventricle is a delicate gray layer, formerly called the middle 
commissure, but now known as the massa intermedia. 

The roof of the ventricle is an epithelial structure. The 
dorsal wall of the embryonic diencejDhalon between the striae 
medullares' remains undeveloped, and stretches between these 
as a layer of epithelial cells. This epithelium, however, is ad- 
herent to a fold of pia mater interposed between the dien- 
cephalon and the telencephalon: the tela chorioidea of the 
third ventricle hereafter to be described, which is often con- 


sidered tlie actual roof. The floor of tlie ventricle is formed 
by the hypothalamus. 

The Hypothalamus. — The hypothalamus (Figs. 6 and 
8), when examined from before backward, presents the follow- 
ing appearances : — 

If, with the brain inverted, one lifts up the optic chiasm, 
there is seen in the median line a sheet of nervous matter : the 
terminal plate (lamina terminalis). Posterior and ventral to 
this is the square mass of the optic chiasm, with the optic nerve 
entering it on each side in front and the optic tract leaving it 
on each side behind. Behind the chiasm is a dark swelling, 
the tuber cinereum, from the ventral surface of which runs 
a slender tube: the infundibulum. The latter terminates in 
an oblong mass about one-half inch in diameter : the pituitary 
body (hypophysis). The hypophysis rests in the sella Turcica 
of the sphenoid bone ; it consists of two portions, or lobes, the 
anterior of which is the larger. Behind the- tuber cinereum on 
each side is a small, shining, rounded body: the mamillary 
body (corpus mamillare). 

If a sagittal section be made through the diencephalon 
(Fig. 8), it will be noticed that the floor of the third ventricle 
is considerably depressed in front, and that the bottom of this 
depressed portion is thrown up into a transverse ridge by the 
optic chiasm. In this way there are produced two small de- 
pressions by the chiasm: one in front,— the optic recess (re- 
cessus opticus), whose anterior wall is the lamina terminalis; 
and the other behind, — the recess of the infundibulum (re- 
cessus infundibuli), whose post-erior wall is the tuber cine- 
reum. The recess of the infundibulum leads into the inf undibr 
ulum, which, it is now seen, is hollow. Roughly speaking, 
only that portion of the hypothalamus which lies behind the 
infundibidum belongs to the diencephalon; it is called the 
mamillary portion of the hypothalamus (pars mamillaris hypo- 
thalami). The remainder of the hypothalamus is the ventral 
part of the telencephalon, and is called the optic portion of 
the hypothalamus (pars optica hypothalami). For the sake 
of convenience they have been described together here. 



^^l"'^- Sp. S.posh. 





Fig. 12." — Scheme of convolutions of lateral surface of cerebral hemisphere 
(after Van Gehuchten). H. fr. s., Superior frontal sulcus. S. proBC, Pre- 
central sulcus. 8. R., Central sulcus of Rolando. S. poste., Post-central sul- 
cus. S. interp., Interparietal sulcus. S. p.o., Parieto-occipital fissure. Ram. 
post. S., Posterior ramus of fissure of Sylvius. S. temp, m., Middle temporal 
sulcus. S. tem,p. s., Superior temporal sulcus. F. 8., Fissure of Sylvius. 
R. ant. asc. 8., Ascending anterior ramus of fissure of Sylvius. R. a. 
h. 8., Horizontal anterior ramus of fissure of Sylvius. 8. fr. inf., Inferior 
frontal sulcus. 



As a result of the rapid growth undergone by the lateral 
portion of the telencephalon in early foetal life, that vesicle is 
greatly elevated on each side of the median line; there is thus 
formed a deep sulcus separating the lateral portions from one 
another. This condition is maintained during subsequent de- 
velopment ; so that in the fully developed encephalon we find 
two more or less symmetrical halves,— the hemispheres (hem- 
isphseria), — separated by a longitudinal fissure (fissura longi- 
tudinalis cerebri). This fissure is complete in front and be- 
hind, but for its middle two-fourths is interrupted ventrally 
by a white body: the corpus callosum. 

The Hemisphere. — Embryologically each hemisphere 
may be divided into the pallium, or the superficial gray matter, 
and the white matter directly connected therewith; the rhi- 
nencephalon, or the central olfactory apparatus; and the 
corpus striatum; but for the purpose of this book it is more 
convenient to first consider the hemispheres as a whole, giving 
attention to its separate parts later. 

The hemisphere is ovoid in shape. It has two surfaces, — 
one lateral and one medial, — and two extremities, — the an- 
terior, or frontal, pole (polus frontalis) ; and the posterior, or 
occipital, pole (polus occipitalis). 

The lateral surface (f acies lateralis) is convex ; it is folded 
in such a way as to present numerous eminences called con- 
volutions (gyri) separated by gTooves called sulci. Certain 
of the sulci are large and deep, and fairly constant, so that 
they may be taken as boundaries by which to divide the hemi- 
sphere on its lateral surface into portions called lobes (lobi). 
Such sulci are commonly called fissures, but in the new nomen- 
clature that term is applied only to such sulci as produce cor- 
responding elevations in the cavity of the hemisphere. The 
most prominent of the fissures is the fissure of Sylvius 
(fissura cerebri lateralis), which may be located in the follow- 
ing way : — 

On the ventral aspect of the telencephalon lateral to the 
optic chiasm there is found a lamina of nervous matter per- 
forated by many foramina for blood-vessels: the anterior per- 


f orated substance. Just lateral to this substance the fissure of 
Sylvius begins; whence it proceeds lateralward to gain the 
lateral surface of the hemisphere, where it divides into three 
branches (Fig. 12). The longest of these, the ramus posterior, 
runs dorsalward and backward, to become gradually lost upon 
the lateral surface; the other two are both short and both 
anterior, the one running nearly vertically dorsalward and 
called the ramus anterior ascendens, the other running nearly 
horizontally forward and called the ramus anterior horizontalis. 

A second fissure is the so-called fissure of Rolando (sulcus 
centralis). It begins on the lateral surface near the longitudi- 
nal fissure at a point a little behind the junction of the anterior 
with the posterior half of the hemisphere, and proceeds for- 
ward and ventralward nearly to the posterior ramus of the 
fissure of Sylvius. 

A third fissure is the parieto-occipital (fissura parieto- 
occipitalis). It begiils on the medial surface of the hemisphere 
behind the posterior extremity of the corpus callosum, and 
passes dorsalward and slightly backward to reach the lateral 
surface, where it disappears after a forward and ventralward 
course of about half an inch. This latter part is frequently 
called the lateral limb of the fissure, the part on the medial 
surface being the medial limb. 

By means of the fissures mentioned the lateral surface is 
divided into five lobes. That portion which lies dorsal to the 
fissure of Sylvius and anterior to the central sulcus of Eolando 
is called the frontal lobe (lobus frontalis) ; that ventral to the 
posterior ramus of the fissure of Sylvius the temporal lobe 
(lobus temporalis); that bounded ventrally by the posterior 
ramus of the fissure of Sylvius, in front by the central sulcus 
of Rolando, and behind by the lateral limb of the parieto-occip- 
ital fissure the parietal lobe (lobus parietalis) ; while the por- 
tion posterior to the lateral limb of the parieto-occipital fissure 
is the occipital lobe. The fifth division is the island of Reil 
(insula). This is found in the depths of the fissure of Sylvius 
where that fissure is dividing into its rami. The island can 
be brought into view by drawing aside the neighboring over- 
hanging convolutions, which collectively are called the oper- 
culum. It will be observed that this division into lobes is far 


from complete, since, except in tke case of tlie island of Keil, 
eacli lobe is connected -.vitli its neighbors bj convolutions pass- 
ing between them, whicli for this reason are called gyri tran- 
sitivi. This statement is especially true of the parietal and 
occipital lobes, between which there is scarcely any well- 
marked boundary. 

Each lobe is divided into several convolutions by sulci as 
follows: The frontal lobe is marked by a sulcus, often atyp- 
ical, running parallel with and anterior to the central sulcus 
of Eolando, — the ascending frontal, or precentral, sulcus (sul- 
cus prsecentralis), — cutting off between itself and the sulcus 
of Eolando a large convolution: the ascending frontal or an- 
terior central convolution (gyrus centralis anterior). From 
the precentral sulcus there proceed forward two other smaller 
sulci, the dorsal, or superior (sulcus frontalis superior), and 
the ventral, or inferior, frontal sulcus (sulcus frontalis in- 
ferior), toward the frontal pole; these divide the remainder 
of the frontal lobe into three convolutions: the dorsal, or 
superior ; the middle ; and the ventral, or inferior, frontal con- 
volutions (gyrus frontalis superior, medius, et inferior). The 
ventral frontal convolution at its ventral margin is divided into 
three parts by the indentations of the anterior rami of the fis- 
sure of Sylvius: the posterior division, behind the ascending 
ramus, is the pars opercularis; the middle, between the rami, 
is the pars angularis; and the anterior division is the pars 
orbitalis. In the course of development the anterior extremi- 
ties of these three frontal convolutions are bent forward and 
ventralward, and then backward;" so that they come to lie upon 
the orbital plate of the frontal bone (Fig. 13), in which situa- 
tion they are called orbital convolutions (gyri orbitales). The 
dorsal frontal here becomes the medial orbital, the middle 
frontal becomes the anterior orbital, and the ventral frontal 
becomes the posterior orbital convolution. The medial or- 
bital convolution borders on the anterior extremity of the 
longitudinal fissure, and contains an antero-posterior groove, 
— the olfactory sulcus, — which lodges a white band, — the ol- 
factory tract ; the portion of the gyrus medial to this sulcus is 
known as the straight convolution (gyrus rectus). 

The parietal lobe contains a fairly-constant sulcus, the 


Fig. 13. — Scheme of convolutions of ventral aspect of eei-ebral hemisphere 
(after Van Gehuchten). Eul. oJf., Olfactory sulcus. Siil. temp, inf., Inferior 
temporal sulcus. Fis. col., Collateral fissure. 


interparietal (snlciTS interparietalis), by means of which it is 
divided into three convolntions. This sulcus begins near the 
posterior ramus of the fissure of Sylvius, and first runs parallel 
with the fissure of Kolando, and then turns backward to termi- 
nate near or in the occipital lobe. As it makes its backward 
turn it gives off an ascending branch, which is sometimes an 
independent sulcus^, — the postcentral (sulcus postcentralis), — - 
which continues the course of t\e parent-sulcus dorsalward. 
The long convolution lying between this latter sulcus and the 
interparietal behind, and the central sulcus of Eolando in front 
is the ascending parietal, or posterior central, convolution 
(gyrus centralis posterior). That portion of the lobe con- 
tained between the posterior part of the interparietal sulcus 
and the longitudinal fissure is the dorsal, or superior, parietal 
lobule (lobulus parietalis superior). The remainder of the 
lobe ventral and posterior to the interpiarietal sulcus is the 
ventral, or inferior, parietal lobule (lobulus parietalis inferior) ; 
its anterior portion bordering the posterior ramus of the fis- 
sure of Sylvius is often termed the supramarginal convolu- 
tion (gyrus supramarginalis) while the posterior part is called 
the angular convolution (gyrus angularis). 

The temporal lobe is divided into five convolutions as 
follows: The portion adjacent to the posterior ramus of the 
fissure of Sylvius is the dorsal, ar superior, temporal con- 
volution (gyrus temporalis superior). It is separated by. an 
antero-posterior sulcus, — the dorsal, or superior, temporal sul- 
cus (sulcus temporalis superior), — from the middle temporal 
convolution (gyrus temporalis medius). The latter convolu- 
tion is separated by another antero-posterior sulcus, the middle 
temporal sulcus (sulcus temporalis medius), from the ventral, 
or inferior, temporal convolution (gyrus temporalis inferior). 
The last two convolutions are especially badly defined. At 
this point the lobe makes a ventral bend toward the median 
line, so as to present upon the ventral aspect of the enceph- 
alon. Here we find two convolutions (Figs. 13 and 14). 
The first is large and spindle-shaped, the fusiform convolu- 
tion (gyrus fusiformis), and is limited laterally by the ven- 
tral, or inferior, temporal sulcus (sulcus temporalis inferior). 
On its medial side it is bounded by a long fissure extending 



5ul. C.C. 


Sid sub f' 



2^73. Ce?k. 

Fig. 14. — Scheme of convolutions on medial surface of cerebral hemisphere 
(after Van Gehuchten). Fis. S., Fissure of Sylvius. Sul. cal. marg., Calloso- 
marginal sulcus. Sul. subf., Subfrontal sulcus. Sul. C. C, Sulcus of corpus 
callosum. Sill, marg., Marginal sulcus. Sul. subp., Subparietal sulcus. 
Fis. P.O., Parieto-occipital fissure. Fis. calc, Calcarine fissure. Fis. den.. 
Dentate fissure. Fis. col.. Collateral fissure. 


almost to the anterior extremity of tlie lobe, the collateral 
fissure (fissura collateralis), medial to the posterior part of 
which is the lingual convolution (gyrus lingualis). 

The occipital lobe may be roughly divided into three 
convolutions: dorsal, or superior; middle; and ventral, or 
inferior. Some make only two divisions of this lobe, with 
several small convolutions in each division; in this case the 
dorsal division is composed of the gyri occipitales superiores, 
and the ventral of the gyri occipitales laterales. 

The island of Eeil contains three convolutions surrounded 
by a circular sulcus (sulcus circularis). This lobe, as we have 
seen, is overhung by the neighboring convolutions, which 
collectively constitute the operculum. As the operculum is 
furnished by the frontal, parietal, and temporal lobes, there 
is a pars frontalis, a pars parietalis, and a pars temporalis 

The medial surface (facies medialis) of the hemisphere 
(Fig. 14) is convoluted like the lateral surface, but its con- 
volutions are, as a rule, larger and less complex in arrange- 
ment. As limits for these convolutions we have, first, the 
medial limb of the parieto-occipital fissure; beginning at the 
ventral extremity of this fissure and running backward usu- 
ally to the posterior extremity of the hemisphere is the cal- 
carine fissure (fissura calcarina), included between which and 
the parieto-occipital fissure is a wedge-shaped convolution, the 
cuneus. Ventral to the calcarine fissure is the lingual con- 
volution already described as a part of the temporal lobe. 
This convolution is continuous in front Avith a narrow con- 
volution hmited ventrally by the collateral fissure, the hippo- 
campal convolution (gyrus hippocampi), the anterior extrem- 
ity of which is recurved so as to resemble a hook, and which, 
therefore, is known as the uncus. The hippocampal convolu- 
tion is limited dorsally by the dentate fissure (fisslira hippo- 
campi), which begins just ventral to the posterior extremity 
of the corpus callosum, and curves forward and ventralward 
nearly to the uncus. In the luiddle of the medial surface is 
seen the sagittal section of the corpus callosum. It is sepa- 
rated from the adjacent convolutions by a sulcus, — the sulcus 
of the corpus callosum (sulcus corporis callosi), — which, be- 




Fig. 15.— OZ. b., Olfactory bulb. 01. tr., Olfactory tract. R., Rostrum of 
corpus callosum. L. f., Longitudinal fissure. P. a., Parolfactory area. Trig., 
Olfactory trigonum. M. St., Medial stria. Ant. com., Region of anterior com- 
missure. L. t.. Lamina terminalis. Op. cJi., Optic chiasm. Op. tr., Optic 
tract. G. s.. Gyrus subcallosus. A. p. s., Anterior perforated substance. 
L. St., Lateral stria. (After His.) 


ginning ventral to tlie anterior extremity of tliat body, arches 
backward over its dorsal surface to terminate behind its poste- 
rior extremity by opening into the dentate fissure. Begin- 
ning in front of the anterior extremity of the corpus callosum 
is the calloso-marginal sulcus (sulcus cinguli), which winds 
dorsalward and backward to a point dorsal to the posterior 
extremity of the corpus callosum; about the middle of its 
course it sends off an ascending branch, — the subfrontal sul- 
cus (sulcus subfrontalis), — and near its termination another 
ascending branch: the marginal sulcus (sulcus marginalis). 
The portion of the hemisphere cut off dorsal to the calloso- 
marginal sulcus is often called the calloso-marginal convolu- 
tion; it will be noticed that it is merely the medial surface 
of the dorsal, or superior frontal, convolution. Between the 
subfrontal sulcus in front and the marginal sulcus behind is 
the paracentral lobule (lobulus paracentralis), which is the 
combined medial surfaces of the anterior and posterior cen- 
tral gyri. The calloso-marginal sulcus (sulcus cinguli) is 
sometimes continued backward nearly to the parieto-occipital 
fissure, and this part of it is called the subparietal sulcus (sid- 
cus subparietalis). Between it, ventrally, the parieto-occipital 
fissure behind, and the marginal sulcus in front, is a large 
square convolution: the prsecuneus. BetAveen the sulcus of 
the corpus callosum ventrally and the calloso-marginal sulcus 
dorsally is a long, narrow convolution: the convolution of 
the corpus, callosum. It will be seen that this is continuous 
with the hippocampal convolution around the posterior ex- 
tremity of the corpus callosum." These two convolutions to- 
gether have been called the limbic lobe of Broca; in the 
nomenclature now employed they constitute the gyrus forni- 
catus, divided into two parts, — the gyrus cinguli, correspond- 
ing to what was called the convolution of the corpus callosum, 
and the gyrus hippocampi, — while their point of union around 
the posterior extremity of the corpus callosum is the isthmus 
gyri fornicati. 

The R]ihiencepliaIo7i. — The rhinencephalon (Tig. 15) is 
developed as an offshoot from the anterior ventral portion of 
the telencephalon. The medial orbital convolution, as we 
have seen, contains an antero-posterior sulcus parallel to the 


anterior extremity of tlie longitudinal fissure: the olfactory 
sulcus (sulcus olfactorius). In this lies a white band, the 
olfactory tract (tractus olfactorius), which, when followed 
forward, is seen to emerge from a small oval enlargement: 
the olfactory bulb (bulbus olfactorius). Behind, at the edge 
of the orbital convolution, the tract develops a small tri- 
angular swelling: the olfactory triangle (trigonum olfac- 
torium). From this triangle set out two small cords: the 
olfactory roots, or striae. The medial root (stria olfactoria 
medialis) runs backward toward the median line, to enter a 
small gray area: the olfactory area of Broca (area parolfac- 
toria). The lateral root (stria olfactoria lateralis) runs back- 
ward and lateralward to enter the anterior extremity of the 
hippocampal convolution. In its course it crosses the ante- 
rior perforated substance (substantia perforata anterior): a 
thin, gray lamella containing numerous foramina for vessels. 
Limiting this lamella medially and behind is a narrow white 
cord running between the anterior extremity of the corpus 
callosum and the hippocampal convolution; it has been called 
the j)eduncle of the corpus callosum, but it is more in accord 
with our present knowledge to regard it as a convolution, 
called, from its position, the gyrus subcallosus. By its means 
the two anterior extremities of the limbic lobe, or gyrus 
fornicatus, are connected. 

It is customary to divide the rhinencephalon into two 
portions: an anterior (pars anterior) and a posterior (pars 
posterior). The former contains the bulb, the tract, the tri- 
angle, the medial stria, and the area parolf actoria ; the latter 
the perforated substance, the lateral stria, and the gyrus 

The Vextral Portiox of the Telexcephalox. — The 
divisions of the telencephalon which we have been studying 
are all developed from that part of the embryonic vesicle 
which lies dorsal to the neural cavity. The ventral portion 
of the telencephalon produces the optic part of the hypo- 
thalamus (pars optica hypothalami); this has already been 
described in the account given of the diencephalon. 


The Ixteexal Anatomy of the Excephalon. 

the ixteexal axatomy of the tiiyelexcephalox. 

Ix tracing the continuity of stnictnre between the me- 
dulla oblongata and the spinal cord we shall find that a 
gradual, but marked, rearrangement of both gTaj and white 
matters occurs; moreover, we shall find structures in the 
medulla which are lacking in the cord. 

This rearrangement of matter begins even in the cord. 
If a section through the first cervical segment of the cord 
(Fig. 16) be examined, it will be noticed that the dorsal horn 
of the gray matter has been bent ventro-laterally in such a 
manner as to describe a curve, the' concavity of which is 
ventral. The neck of the horn is much thinned, while the 
gelatinous substance of Rolando (substantia gelatinosa) is 
enlarged, and is capped laterally by the cross-section of a 
bundle of slender nerve-fibres. These fibres are derived from 
the fifth cranial, or trigeminal t*nerve. In the study of the 
surface anatomy of the pons Varolii we have seen that this 
nerve pierces the ventral surface of the pons; in its sub- 
stance the sensory fibres of the nerve, after the manner of 
sensory nerves in general, bifurcate into ascending and de- 
scending branches: the latter run as far as the first segment 
of the cord. They constitute the spinal tract of the trigem- 
inal nerve (tractus spinalis nervi trigemini), the cross-section 
of which appears very distinctly all through the posterior 
portion of the pons and through the entire extent of the me- 
dulla. It is accompanied by the gelatinous substance, which 
is situated medial to it, and is the terminal nucleus of its 
fibres (nucleus tractus spinalis nervi trigemini). In the cer- 
vical region of the cord the gray matter exhibits the so-called 
lateral horn, from which the fibres of the eleventh cranial, 
or spinal accessorv, nerve arise. This nucleus is continued 



D.pyln "'^.h. 

Fig. 16. — D. 7/., Dorsal lion. XI, Spinal accessory nerve. F. r., Formatio 
reticularis. 1. //., Ventral horn. T. r. f., Ventral root-fibres. T'., Spinal 
tract of trigeminal nerve. Siihs. (jcL. Substantia gelatinosa. F. G., Funicu- 
lus of Goll (funiculus gracilis). F. i?., 'Funiculus of Burdaeli (funiculus 
cuneatus). C. pij. tr., Crossed pyramidal tract (fasciculus cerebro-spinalis 
lateralis). D. c. tr., Direct cerebellar tract (fasciculus cerebello-spinalis). 
Gotv., Tract of Gowers (fasciculus antero-lateralis superficialis). L. y. b., 
Lateral ground-bundle (fasciculus lateralis proprius). T. g. 5., Ventral 
ground-bundle (fasciculus anterior proprius). D. pij. tr.. Direct pyramidal 
tract (fasciculus cerebro-spinalis anterior). 


into the posterior part of the medulla, Avliere it keeps the same 
relative position. 

Lateral to the gray matter in the cervical portion of the 
cord appears the formatio reticularis: a net-work of trans- 
verse and longitudinal fibres, vhich attains much fuller de- 
velopment in the medulla. 

An important factor in the rearrangement of the white 
and gray matters is the decussation of the pyramids (Fig. 17). 
The pyramids of the medulla are composed of fibres which 
arise in certain convolutions of the telencephalon, and con- 
vey impulses to the nuclei of origin of the motor peripheral 
nerves. On arriving at the spinal end of the medulla the 
great majority of these fibres cross the median line to the 
lateral column of the opposite side of the cord, where they 
form the crossed pyramidal tract (fasciculus cerebro-spinalis 
lateralis); a few remain uncrossed, and descend in the ven- 
tral column of the cord as the direct pyramidal tract (fascic- 
ulus cerebro-spinalis anterior). The decussating fibres, cross- 
ing from the pyramid of one side to the lateral column of the 
other, pass through the base of the ventral horn, and sever it 
from the central gray matter. If we follow these fibres in 
the opposite direction, — i.e., from the cord to the medulla, 
— it will be seen that in the medulla they occupy the region 
corresponding to that which thss* ventro-lateral ground-bundle 
occupies in the cord. The latter bundle continues its course 
into the medulla, and there lies dorsal to the pyramid and 
ventral to the central canal. The other tracts of white matter 
maintain the same relative positions in the posterior part of 
the medulla as in the cord. 

Ventral to the funiculus of GoU (funiculus gracilis) is 
a gray mass continuous with the dorsal horn; a similar, but 
more rounded, mass is ventral to the funiculus of Burdach 
(funiculus cuneatus). As we follow these objects through 
the medulla (Fig. 18), the gray masses steadily increase in 
size, the lateral one extending farther forward, until" they 
terminate in the enlargements which we have called the clava 
and the cuneate tubercle. The funiculi of white matter dor- 
sal to them, however, become gradually thinner, imtil at the 
level of the clava and cimeate tubercle, respectively, they 






Fig. 17. — F. G., Funiculus of Goll. N. f. G., Nucleus of the funiculus of 
Goll. F. B., Funiculus of Burdach. N. f. B., Nucleus of the funiculus of 
Burdach. XI, Spinal accessory nerve. Tr. sp. n. trig., Spinal tract of the 
trigeminal nerve. S^l'bs. gel., Substantia gelatinosa. C. ven., Ventral horn. 
D. P., Decussation of the pyramids. Ten. gr. huinl., Ventro-lateral ground- 
bundle. (After Henle.) 


cease altogether. The gray masses, then, are the terminal 
miclei of the fnniculi of Goll and BurJach (nucleus funiculi 
gracilis; nucleus funiculi cuneati). 

]^umerous fibres are seen sweeping across each half of 
the section toward the median line in curves with the con- 
cavities dorsal: the internal arcuate fibres (fibrae arcuata^ in- 
ternae). Thev are in great part the axones of cells situated in 
the nuclei of the funiculi of Goll and Burdach. On reach- 
ing the median line, they cross to the opposite side and take 
a longitudinal direction forward, occupying the same region 
as the ventro-lateral ground-bundle from the cord, and with 
the latter form the prominent tract of fibres known as the 
medial lemniscus (lemniscus medialis). The crossing in the 
median line of these arcuate fibres from both sides constitutes 
the decussation of the lemnisci (decussatio lemniscorum), 
while the median line in which they decussate is called the 
raphe. Since many of the fibres of the lemniscus are derived 
from the terminal nuclei of the funiculi of Goll and Bur- 
dach of the opposite side, each lemniscus may be regarded as 
the indirect continuation of these funiculi. Here, then, in 
the posterior part of the medulla are two great decussations: 
the ventral one of motor fibres, the dorsal one of sensory 
fibres. These fibres are the principal conducting-tracts be- 
tween the cortex of the telencephalon and the peripheral 
nerves, and we shall meet them in all the succeeding portions 
of the encephalon. 

Many of the internal arcuate fibres are axones from the 
cells in the substantia gelatinosa, the terminal nucleus of the 
spinal tract of the trigeminal nerve. Tarther forward many 
are likewise derived from the nuclei of other sensory cranial 
nerves. These arcuate fibres from the nuclei of sensory nerves 
also cross the raphe, but the course pursued by them thereafter 
is not definitely settled, some holding the opinion that they 
travel in the medial lemniscus, while others believe that they 
form separate tracts in the dorsal part of the formatio fetic- 
idaris. Certainlj^ some of them, at least, join the lemniscus 
of the opposite side from that in which they arise. In the 
case of the nerve of hearing we shall see hereafter that the 
fibres which arise in its terminal nuclei form a separate tract. 





Fig. 18. — 'Nuc. XII, Nucleus of hypoglossal nerve. 'Nuc. XI, Nucleus of 
spinal accessory nerve. F. B., Funiculus of Burdach. Tr. sp. n. trig., Spinal 
tract of trigeminal nerve. D. c. tr., Direct cerebellar tract. Goic, Tract of 
Gowers. XI, Spinal accessory nerve. PW-, Pyramid. XII, Hypoglossal 
nerve. Dec. lem.. Decussation of lemniscus. Int. arc. fih., Internal arcuate 
fibres. Suits, gel., Substantia gelatinosa. K. f. B., Nucleus of funiculus of 
Burdach. ISf. f. G., Nvicleus of funiculus of GoU. 


Many of the arcuate fibres are derived from the pyra- 
mids, crossing the median line to reach the nuclei of origin 
of the motor nerves, and still others are fibres connecting the 
sensory with the motor nuclei. 

Finally we have to note the changes which occur in the 
central canal. As the fourth ventricle is approached, the 
diameter of the canal increases, until at the level of the 
termination of the funiculus of Goll in its nucleus the canal 
is covered only by the thinned, dorsal, gray commissure. At 
last the dorsal wall becomes reduced to its epithelial lining, 
which, as we have seen, is continuous with the epithelium 
lining the ventral surface of the tela chorioidea of the fourth 
ventricle, and the canal is now said to have "opened out" into 
the ventricle. 

Proceeding to the study of the anterior portion of the 
medulla, we begin with a section through the posterior ex- 
tremity of the calamus scriptorius (Fig. 19). The funiculus 
of Goll and its nucleus have ceased to exist, but the funiculus 
of Burdach, though much smaller than before, is still present. 
The semilunar section of the trigeminal nerve lying lateral 
to its nucleus is a prominent feature. It will be noted that 
this tract does not here reach the periphery of the medulla, 
but has lateral to it a bundle of oblique fibres; this bundle 
is the direct cerebellar tract froi'u the spinal cord (fasciculus 
cerebello-spinalis), which, having ascended in the lateral tract 
of the medulla, in this region makes a dorsal bend to enter 
the corpus restiforme. The tract of Gowers (fasciculus antero- 
laterahs superficialis) keeps the same position ventral to the 
direct cerebellar tract. 

Farther ventral is the section of the olive, which here 
shows as three pieces: a dorsal, or dorsal accessory olivary 
nucleus (nucleus olivaris accessorius dorsalis); a medial, or 
medial accessory olivary nucleus (nucleus olivaris accessorius 
medialis); and a central portion, or inferior olivary nucleus 
(nucleus olivaris inferior). The latter is by far the largest;, 
it is a convoluted lamina of gray matter with an opening, the 
hilus, toward the raphe, through which pass numerous fibres 
which connect it with the cerebellar hemisphere of the op- 
posite side: the cerebello-olivary fibres. 



NiicXII NuC.f^.B 



Tvsp. n . trig. 

Subs, gel- 
X ^ 

_ -Nucamh- 
'.int. I em. 


Fig. 19. — 'NuG. XII, Nucleus of hypoglossal nerve. 'Nuc. a. c, Nucleus of 
ala cinerea. Ishic f. B., Nucleus of funiculus of Burdacli. F. B., Funiculus 
of Burdach. Tr. sol., Tractus solitarius. Tr. sp. n. trig.. Spinal tract of 
trigeminal nerve. Subs, gel., Substantia gelatinosa. X, Vagus nerve. 
D. C. tr., Direct cerebellar tract. Nuc. ami).. Nucleus ambiguus. Goio., Tract 
of Gowers. St. int. lem., Interolivary stratum of lemniscus. C. 0. jf., Cere- 
bello-olivary fibres. Pyr., Pyramid. N. a. 0. m., Medial accessory olivary 
nucleus. XII, Hypoglossal nerve. :N. o. inf., Inferior olivary nucleus. 
IV. a. 0. d., Dorsal accessory olivary nucleus. 


On eacli side of the ventral median snlcns is the pyra- 
mid. Dorsal to the pyramid is the bundle of sensory fibres 
which farther forward goes to form the medial lemniscus, 
seen as a triangular tract between the olives and hence known 
as the interolivary layer (stratum interolivare lemnisci); the 
most dorsal of the fibres near the raphe in this situation are 
continuous farther forward with the medial longitudinal 
bundle (fasciculus longitudinalis medialis): a tract of fibres 
which will become much more evident as we proceed. These 
fibres correspond to those of the ventral ground-bundle of 
the spinal cord. In the floor of the ventricle are the nuclei 
of some of the cranial nerves. On each side of the median 
line is a collection of large cells: the nucleus of origin of the 
twelfth cranial or hypoglossal nerve. The root-fibres of the 
nerve are conspicuous, running ventro-lateralward medial to 
the olive to escape from the medulla through the ventro- 
lateral sulcus. This nucleus consists of a long column of cells 
extending from the level of the decussation of the pyramids 
nearly to that of the strige acusticas. In the posterior part 
of the medulla the nucleus lies ventro-lateral to the central 
canal; in the anterior portion it corresponds to the trigonum 
hypoglossi in the floor of the ventricle. 

Lateral and somewhat dorsal to the nucleus of the twelfth 
is the terminal nucleus of the scaisory portion of the tenth 
cranial, or pneumogastric or vagus, nerve (nucleus alse cine- 
re^). Most of the sensory fibres of the nerve end in this 
nucleus, but some descend after the manner of the spinal 
tract of the trigeminal nerve, forming a part of a small bun- 
dle dorsal and lateral to the nucleus of the ala cinerese: the 
tractus solitarius. Around the latter is a column of gray 
matter in which the fibres of the tract end: the nucleus of 
the solitary tract (nucleus tractus solitarii). These two nuclei 
are really common to both the tenth and the ninth (glosso- 
pharyngeal) cranial nerves, the latter terminating in their 
more anterior portions. The tractus solitarius consists, in "the 
main, of fibres derived from the glosso-pharyngeal nerve. 
Moreover, both of these nerves are mixed nerves: i.e., they 
contain both motor and sensory fibres. ISTow, the nucleus of 
origin of the motor fibres is the nucleus ambiguus. The ven- 






Pim Ml 

Fig. 20. — Isiuc. XII, Nucleus of hypoglossal nerve, l^^uc. a. c, Nucleus of 
ala cineiea. Tr. sol., Tractus solitarius. D. r. Till, Descending root of 
vestibular nerve. C. v., Corpus restifovnie. Tr. sp. T., Spinal tract of tri- 
geminal nerve. *S'w?>s. gel.. Substantia gelatinosa. IX, Glosso-pliaryngeal 
nerve. A', Vagus nerve. C. 0. f., Cerebello-olivaiy fibres. Gow., Gowers's 
tract. Xiic. ami).. Nucleus ambiguus. X. a. o. d., Dorsal accessory olivary 
nucleus. X. o. inf., Inferior olivary nucleus. XII, Hypoglossal nerve. Pyr., 
Pyramid. St. int. Zem., Interolivary stratum of the lenmisciis. 



tral liorn of the cord, after being cut off by tlie decussating 
pyramid, does not disappear entirely, but continues forward 
in tbe medulla, to furnish nuclei for several cranial nerves. 
It thus furnishes that for the ninth and tenth cranial nerves, 
— the nucleus ambiguus, — which is located about midway be- 
tween the olive and the gelatinous substance and dorsal to a 
line connecting them. Its axones take a dorso-lateral route, 
and join the sensory fibres. It will be observed that the root- 
fibres of these two nerves run through the spinal tract of the 
trigeminal nerve and the gelatinous substance. 


Fig. 21. — B. eoft. arc, Dorsal external arcuate fibres. D. c. tr., Direct 
cerebellar tract. Y. ext. arc, Ventral external arcuate fibres. (After 

The internal arcuate fibres are very numerous, sweeping 
across the section from all the sensory nuclei. That portion 
of the section through which they pass — between the floor of 
the ventricle, the medial lemniscus, the inferior olive, and the 
gelatinous substance — is the fully-developed formatio reticu- 
laris of the medulla : a mixture of white and gray matter "be- 
lieved to be associational in function. 

The next section (Fig. 20) passes through all three of 
the triangular areas into which the calamus scriptorius is 
divided, the trigonum hypoglossi containing the nucleus of 






Fig. 22.— M. Z. b., Medial longitudinal bundle. Suhs. gel., Substantia 
gelatinosa. Med. Urn., Medial lemniscus. Pyr., Pyramid. 2V. o. int, In- 
ferior olivary nucleus. 2V. «. o. d, Dorsal accessory olivary nucleus. Goxc, 
Gowers's tract. Tr. sp. n. trig., Spinal tract of trigeminal nerve. C. r., 
Corpus restiforme. N. ii. c. d.. Dorsal nucleus of cochlear nerve. D. r. YIII, 
Descending root of vestibular nerve. A^. d. r. Till, Nucleus of descending 
root of vestibular nerve. St. (ic, Acoustic striae. 


the hypoglossal nerve, the ala cinerea containing the terminal 
nuclei of the ninth and tenth cranial nerves, and the acoustic 
area. In this situation the latter contains the descending root 
of the vestibular nerve and its accompanying nucleus medial 
to it. Lateral and ventral to this is seen the cross-section of 
the corpus restiforme. It is composed of fibres from several 
sources: first, the direct cerebellar tract from the cord, which 
is here seen entering it; second, the cerebello-olivary fibres; 
and, third, the external arcuate fibres. The cerebello-olivary 
fibres connect the cerebellar hemisphere of one side with the 
olive of the opposite side. They run in the corpus restiforme, 
appear among the most ventral of the internal arcuate fibres, 
traverse the olive of the same side, cross the raphe, and enter 
the olive of the opposite side. The external arcuate fibres 
consist of two sets (Fig. 21): a dorsal, derived from the nuclei 
of the funiculi of Goll and Burdach, and a ventral, which 
emerge from the interolivary layer of the lemniscus to wind 
around the lateral surface of the medulla and enter the corpus 

In Eig. 22 the section passes through the acoustic strise. 
Laterally these fibres are connected with a semilunar mass of 
gray matter dorso-lateral to the corpus restiforme: the acous- 
tic tubercle, or dorsal nucleus of the cochlear nerve (nucleus 
nervi cochleae dorsalis). The acoustic nerve at the medulla 
is composed of two parts: a postero-lateral, or cochlear, 'por- 
tion (radix cochlearis); and an antero-medial, or vestibidar, 
portion (radix vestibularis). Xow, the acoustic tubercle is 
one of the terminal nuclei of the cochlear portion. The axones 
from the cells of this nucleus form the acoustic striae, which 
arch in the floor of the ventricle first dorsalward and then 
ventral ward toward the median line; just ventral to the 
median sulcus most of them cross the median line, and their 
subsequent course will be described hereafter. 

The nuclei of the twelfth, tenth, and ninth cranial nerves 
have ceased to exist at this level of the medulla, while the, 
descending root of the vestibular nerve is larger in volume. 

The medial longitudinal bundle here begins to show as 
a distinct tract; it will be noticed that its fibres are larger 
than those of the medial lemniscus. 



Fig. 23. — A., p. c, Anterior peduncle of cerebellum. C. f. r., Fibres from 
vestibular nerve to cerebellum. N. B., Nucleus of Bechterew. Is. D., Xucleus 
of Deiters. C. v., Corpus restiforme. T'. Till, Root-fibres of vestibular nerve. 
N. V. n. c, A^entral nucleus of cochlear nen-e. C. Till, Cochlear portion of 
acoustic nerve. Till, Acoustic nerve. C. trap.. Trapezoid body. Tr. sp. 
n. tri(j., Spinal tract of trigeminal nerve. N. o. inf., Inferior olivary nucleus. 
Pyr., Pyramid. Med. lem.. Medial lemniscus. ^((C'. T7/, Xucleiis of facial 
nerve. M. I. 1)., Medial longitudinal bundle. Suhs. gel.. Substantia gelatinosa. 
M. 11. v.. Medial nucleus of vestibular nerve. 



The Pox^s Yajrolii. — We sliall begin tlie stndj of tlie 
pons by examining a section throngli the transition-plane be- 
tween tbe medulla and j)ons (Fig. 23). Here we find, as in 
preceding sections, the pyramid, the olive, the internal arcuate 
fibres and medial lemniscus, the medial longitudinal bundle, 
and the spinal tract of the trigeminal nerve; but the pre- 
dominant feature of the section is presented by the nuclei of 
the eighth cranial or acoustic nerve. The acoustic tubercle 
is no longer seen, biit ventro-lateral to the corpus restif orme, 
which is now entering the cerebellum, is the principal nucleus 
of termination of the cochlear nerve, the A'entral nucleus 
(nucleus nervi cochleae ventralis), characterized by the large 
number of nerve-fibres contained in it and by their "basket- 
work-like" arrangement around gToups of cells. The acoustic 
nerve consists of two distinct bundles: the one arises from 
the ganglion of Corti in the cochlea, and is therefore called 
the cochlear nerve (nervus cochleae) ; while the other springs 
from the ganglion of Scarpa in the vestibule, and is termed 
the vestibular nerve (nervus vestibuli). As the acoustic nerve 
approaches its termination, the cochlear nerve enters the ven- 
tral nucleus, where it bifurcates, sending a part of its fibres 
into the dorsal nucleus, the others ending in the ventral 
nucleus. A series of sections shows that the dorsal nucleus 
is continuous with the ventral nucleus, although it does not 
extend as far forward as the latter. In the dorsal nucleus the 
acoustic striae take their origin; the ventral nucleus sends its 
axones, seen better in the next section, nearly transversely into 
the pons, where they form the trapezoid body (corpus trape- 

The fibres of the vestibular nerve enter the pons and run 
toward the flood of the ventricle ; near it, in the area acustica, 
they reach their principal nucleus of termination, the medial 
(nucleus nervi vestibuli medialis) : a large gray mass extend- 
ing in the floor of the ventricle from its lateral wall almost 
to the median line. Here the vestibular fibres divide into 
their ascending and descending branches. Most of the former 
terminate in the medial nucleus, but some turn laterally to 



A, p. 


Fig. 24. — M. n. v., Medial nucleus of vestibular nerve. Niic. YI, Nucleus 
of abducens nerve. G. Til, Genu of facial nerve. M. J. h.. INIedial longi- 
tudinal bundle. P. p. VII, Pars prima of facial nerve. YI, Root-fibres of 
abducens nerve. 0. a., Anterior oliAje. Med. Jem., Medial lemniscus. D. t. f., 
Deep transverse fibres of pons. Pyr., Pyramidal tract. S. t. f., Superficial 
transverse fibres of pons. N. p., Nuclei pontis. Nvc. YII, Nucleus of facial 
nerve. C. tf-ap., Trapezoid body. P. s. YII, Pars secunda of facial nerve. 
Tr. sp. Y., Spinal tract of trigeminal nerve. A. p. c, Anterior peduncle of 


disappear iu the superior nucleus of Becliterew and in tlie 
cerebellum. The descending branches form the descending 
root of the vestibular nerve, which we have seen extending as 
far as the termination of the funiculus of Burdach accompanied 
bj its terminal nucleus, which lies medial to it and which is a 
prolongation from the medial nucleus. 

As the vestibular fibres approach the floor of the ven- 
tricle they traverse a scattered collection of large cells medial 
to the dorsum of the corpus restiforme known as the nucleus 
of Deiters (nucleus nervi vestibuli lateralis); similarly the 
cerebellar fibres of this nerve pass through another nucleus 
dorso-lateral to that of Deiters: the nucleus of Bechterew 
(nucleus nervi vestibuli superior). 

Another new feature of this section is the nucleus of 
origin of the seventh cranial, or facial, nerve. It may be 
looked upon as a forward continuation of the nucleus ambiguus, 
and occupies the same relative position as that nucleus. 

The next section (Fig. 24) is entirely within the pons. 
Sections of the pons are divided into two parts: dorsal (pars 
dorsalis); and ventral, or basilar (pars basilaris). 

In the ventral portion we find two sets of fibres: longi- 
tudinal and transverse. The former are, in the main, the fibres 
which in the medulla constitute the pyramids, and which may 
be still called the pyramidal tracts; they are broken up into 
several bundles (fasciculi longitudinales) in the pons by trans- 
verse fibres. 

The transverse fibres are divided into two sets according 
to their relation to the longitudinal: those which run ventral 
to the pyramidal tracts (fibrse transversse superficiales), and 
those dorsal to the pyramidal tracts (fibrse transversse pro- 

Interspersed among these transverse fibres are several 
masses of gray matter:, the nuclei of the pons (nuclei pontis). 

Some of the transverse fibres pass entirely across the sec- 
tion, being fibres which connect the two hemispheres- of the 
cerebellum; others come from the cerebellum and end in the 
nuclei pontis; and still others run from the nuclei pontis to 
the cerebellum. 

The ventral portion of the pons maintains "essentially the 




Fig. 25.— Scheme of the nuclei and root-fibres of the cranial nen'es 
(after Edinger). 


same appearance tlirougliout the pons, and need not be de- 
scribed again. 

Turning now to tlie dorsal portion of the pons, it is seen 
that the medial lemniscus occupies the same position as in 
previous sections, but is somewhat flattened. The inferior 
olivary nucleus has disappeared, and the medial lemniscus is 
now clearly separated from the medial longitudinal bundle. 
Lateral to the medial lemniscus is a folded sheet of gray mat- 
ter: the anterior (superior) ohve (nucleus olivaris superior). 
Running transversely ventral to this are the fibres of the 
trapezoid body, which, as we have seen, are, in the main, the 
axones of cells of the ventral cochlear nucleus. Some of them 
terminate in the anterior olive' of the same side, while others 
cross the median line to end in the anterior olive of the op- 
posite side. 

Dorsal and lateral to the olive is the nucleus of origin 
of the facial nerve. In this section the root-fibres of this 
nerve have been di^^ded in three places, owing to the fact 
that they pursue a very complex course in the substance of 
the pons (Fig. 25). After their origin the fibres take a dorso- 
medial direction until they reach the floor of the ventricle near 
the median line (pars prima); then they run longitudinally 
forward to make a lateral bend and curve dorsal to the nucleus 
of the sixth cranial or abducens ner. e (genu) ; and finally 
assume a ventro-lateral direction to pass between their own 
nucleus and the gelatinous substance (pars secunda), and make 
their exit. 

In the hollow of the genu of the facial is the nucleus of 
origin of the sixth cranial, or abducens, nerve. Its root-fibres 
run ventralward, with an inclination backward, to escape in 
the transverse sidcus between the pons and the medulla. 

Lateral to the pars secimda of the facial is the spinal tract 
of the trigeminal nerve, Avith its terminal nucleus; and in the 
extreme lateral area of the floor of the ventricle is still a por- 
tion of the medial vestibular nucleus, with a few root-fibres 
entering it. 

Bordering the ventricle is the cross-section of the anterior 
peduncle of the cerebellum (brachium conjunctiATim). 

The next section (Lig. 26) passes through the domain of 




'„ 'ill.^^ri A.n.C. 

Fig. 26. — F. F., Anterior medullary velum. A. p. c. Anterior peduncle 
of cerebellum. P. m. n. v., Principal motor nucleus of the trigeminal nerve. 
X. ^. v., Sensory nucleus of trigeminal nerve. M. v., INIotor root-fibres of 
trigeminal nerve. »S'. v., Sensory root-fibres of trigeminal nerve. C. trap., 
Trapezoid body. 0. a., Anterior olire. Pyr., Pyramidal tract. S. t. f., Super- 
ficial transverse fibres of the pons. D. t. f., Deep transverse fibres of the 
pons. i\'. p., Nuclei pontis. Med. lem., Medial lemniscus. M. I. &., Medial 
longitudinal bundle. A. f. v., Arcuate fibres of the trigeminal nerve. 


tlie nuclei of tlie trigeminal nerve. As that nerve appears at 
the ventral surface of the pons it presents two divisions or 
roots, the larger, or sensory, portion (portio major) being 
posterior and lateral to the smaller, or motor, root (portio 
minor). The terminal nucleus of the sensory portion is situ- 
ated deep in the lateral area of the pons; here the fibres divide 
into ascending and descending branches; the latter accom- 
panied by their nucleus of termination we have seen in all 
the preceding sections as the spinal tract of the trigeminal 
nerve. Most of the ascending branches terminate in the large 
nucleus seen in this section, which may be regarded as the 
anterior extremity of the substantia gelatinosa, but some turn 
laterally to enter the middle peduncle of the cerebellum. 

The anterior, or motor, root of the trigeminal nerve has 
two nuclei of origin, the principal one of which is seen in this 
section (nucleus motorius princeps nervi trigemini) as a small 
mass of large cells medial to the sensory nucleus. Between 
these two nuclei a band of fibres iims toward the floor of the 
ventricle, then turns medial ward, and, passing just beneath 
the floor of the ventricle, decussates with a similar tract from 
the other side. These fibres are often called the arcuate fibres 
of the trigeminal, but neither their origin nor their termina- 
tion has been definitely determined. 

Between the medial longitudinal bundle and the medial 
lemniscus is quite a large collection of gray matter in the 
raphe and on each side called the central nucleus of the pons 
(shown in Mg. 2Y). 

It will be noticed that the anterior olive is placed farther 
lateral than in the preceding section. 

The last section of the pons that we shall examine (Fig. 
27) is through the extreme anterior part of the fourth ven- 
tricle. In the anterior medullary velum covering the ven- 
tricle is the decussation of the fourth cranial, or trochlear, 
nerve. The trochlear nerve springs from a nucleus in the 
floor of the aqueduct of Sylvius farther forward at the level 
of the posterior (inferior) coUiculi; it then runs in a dorsal 
and posterior direction to gain the anterior medullary velum, 
in which it entirely crosses to the opposite side. 

Lateral to the ventricle is a small bundle of fibres semi- 





Cen nuc^ 

Me diem. -^ 

Fig. 27. — lY, Trochlear nerve. Aq. S., Aqueduct of Sylvius. D. r. V., 
Descending root of the trigeminal nerve. N. d. r. v., Nucleus of descending 
root of trigeminal nerve. A. p. c, Anterior peduncle of the cerebellum. 
Lat. lem., Lateral lemniscus. Nuc. hit. lem., Nucleus of lateral lemniscus. 
Med. lem., Medial lemniscus. Cen. nvc, Central nucleus of pons. Loc. ccer., 
Locus coeruleus. Pyr., Eegion of pyramidal tract. N. i)., Nuclei pontis. 


lunar on cross-section; tliis is tlie descending root of tie tri- 
geminal nerve (radix descendens nervi trigemini). It arises 
from cells in the neighborhood of the locus cceruleus, which 
lies medial and ventral to it. These cells constitute the minor 
motor nuclei of the trigeminal nerve (nuclei motorii minores 
nervi trigemini). The descending root can be traced in the 
lateral wall of the aqueduct of Sylvius as far forward as the. 
level of the anterior (superior) colliculi. Its fibres descend 
to join those springing from the principal motor nucleus. 

Yentral to the ventricle on each side of the median line 
is the medial longitudinal bundle, prominent on section as a 
triangular tract of large fibres. 

The medial lemniscus is now so flattened that its trans- 
verse diameter exceeds the vertical; moreover, it has retired 
from the raphe, and joined neai-ly at right angles another 
tract: the lateral lemniscus (lemniscus lateralis). At the 
angle of junction is situated a small mass of gray matter : the 
nucleus of the lateral lemniscus (nucleus lemnisci lateralis). 
A series of sections through this region shows that the nucleus 
of the lateral lemniscus is continuous with the anterior ex- 
tremity of the anterior olive. iSTow, we have seen that the 
fibres of the trapezoid body, derived in part from the ventral 
nucleus of the cochlear nerve, terminate in the anterior olive 
of both sides. From each olive and nucleus of the lateral 
lemniscus arises another set of fibres, which together with 
the striae acusticas, probably, of the other side compose the 
lateral lemniscus. Consequently the lateral lemniscus is re- 
garded as the path toward the cerebrum of impulses brought 
to the pons by the cochlear nerve: i.e., as a part of the audi- 
tory conduction-path. 

In the ventral portion of the section it will be noticed 
that the aggregate area of the longitudinal fibres is greater 
than in the preceding sections of the pons; this is due to the 
fact that many of the longitudinal fibres are distributed, to 
the motor nuclei of cranial nerves and to the nuclei pontis in 
the anterior portion of the pons. Since the fibres distributed 
to the nuclei pontis arise in the cortex of the telencephalon, 
they are called cortico-pontile fibres. 



Fig. 28.— Longitudinal section of the hemisphere of the cerebellum 
(after Gray). 



An antero-posterior median section tlirougli the worm 
of the cerebellum shows the characteristic arrangement of 
its white and gray matters (Fig. 8). The white matter is 
internal, and consists of a central mass, or trunk, from which 
prolongations or limbs proceed in various directions, the whole 
constituting the arbor vitse. The primary branches emit still 
smaller secondary branches, which are invested by the super- 
ficial gray matter, or cortex (substantia corticalis). The depth 
of the larger sulci separating the various lobules can now be 
appreciated. The white matter of the worm is continuous on 
each side with that of the hemisphere, and in front with the 
anterior medullary velum, resting on the dorsum of which is 
a small lobule of the worm called the lingula. 

In the hemispheres the arrangement of the two matters 
(Fig. 28) is quite similar to that in the vermis. The trunk 
of the arbor, however, is larger, and contains a folded lamella 
of gray matter — named, from its serrated appearance, the 
nucleus dentatus — situated just lateral to the worm. A much 
smaller nucleus is found in the ventral extremity of the ante- 
rior vermiform process on each side of the middle line: the 
nucleus fastigii. Lateral to the nucleus fastigii are located 
two other nuclei: the nucleus gioborus and the nucleus em- 

In addition to the fibres which connect the two hemi- 
spheres and to those which connect different parts in the same 
division, the white matter of the cerebellum consists of fibres 
which bring it into communication with other portions of the 
central nervous system. Although much study has been de- 
voted to the termination of the fibres which enter the cere- 
bellum as well as to the destination of those which originate 
in its gray matter, our knowledge in both particulars is far 
from exact; so that at the present time only a provisional 
account can be given of the connections of the cerebellum. 
These connections are established mainly through its several 
peduncles. We begin with the inferior peduncle, or corpus 
restiforme. This, we have learned, contains three .sets of 
fibres: the direct cerebellar tract from the cord; the cere- 


bello-olivary fibres, running both ways between the inferior 
olivary nucleus of one side and the hemisphere of the cere- 
bellum of the other; and the extei-nal arcuate fibres, ventral 
and dorsal. Thus, the cerebellum is connected by the direct 
cerebellar tract with Clarke's cells (nucleus dorsalis) of the 
cord, by the cerebello-olivary fibres with the olive of the op- 
posite side of the medulla, and by the external arcuate fibres 
with the terminal nuclei of the dorsal funiculi of the cord on 
the same and on the opposite side. It has been generally 
thought that the direct cerebellar tract terminates in the 
nucleus fastigii of the worm; but recent investigations ren- 
der it probable that this tract ends, in part at least, in the 
cortex of the hemisphere, and that, indeed, all the fibres which 
enter the cerebellum by way of the corpus restiforme may 
reach the cortex. 

The middle peduncle of the cerebellum (brachium pontis) 
contains two sets of fibres: the ponto-cerebellar fibres, which 
arise in the nuclei pontis and terminate chiefly in the hem- 
isphere of the opposite side; and the cerebello-pontile fibres, 
which run from the hemisphere to the pons, where some of 
them terminate in the nuclei pontis and others go to an un- 
known destination. 

The anterior, or superior, peduncle (brachium conjunc- 
tivum) is composed of fibres which arise, according to some 
authorities, in the nucleus dentatus ; according to others, partly 
in the cortex of the hemisphere. They enter the mesenceph- 
alon, where they decussate, and terminate in a gray mass there 
found, called the red nucleus (nucleus ruber). 

In addition to these the cerebellum has two other con- 
necting tracts. In studying the sections of the pons and me- 
dulla we saw that the vestibular nerve sends a fasciculus into 
the cerebellum; the trigeminal, glosso-pharyngeal, and vagus 
nerves possibly do the same thing. In the case of the vestib- 
ular nerve the bundle has been traced to the nucleus fastigii 
of the worm. Some fibres, .then, of the sensory cranial nerves 
run directly into the cerebellum. 

The second is the tract of Gowers from the cord. Al- 
though this tract is in reality very complex, a large proportion 
of its fibres runs forward as far as the level of entrance of 


the sensory portion of the trigeminal nerve. The fibres then 
tnrn dorsahvard, and, having reached the level of the ante- 
rior medullary velum, run backward medial to the anterior 
]3edimcle to end in the cortex of the worm. 

Finally, the results of many investigators point to the 
existence of fibres which, originating in the gray matter of 
the cerebellum, establish connection with the cells of the 
ventral horns of the cord. Unfortunately, our knowledge 
concerning them is quite indefinite. It would seem that 
one important connection is established by way of Deiters's 


We begin the study of the mesencephalon by examining 
a transverse section through the posterior, or inferior, coUiculi 
(Fig. 29); the ventral portion of such a section, however, 
passes through the anterior margin of the pons. The fourth 
ventricle has now given place to the aqueduct of Sylvius 
(aquseductus cerebri): a narrow canal whose walls contain a 
considerable amount of gray matter. In this gray matter 
ventro-lateral to the aqueduct lies the nucleus of origin of 
the fourth cranial, or trochlear, nerve (nervus trochlearis). 
Its root-fibres curve dorsalward with an inclination tow^ard the 
median line, then take a posterior direction to enter the ante- 
rior medullary velum, where they cross the median line and 
appear as the nerve lateral to the peduncle of the cerebrum. 

Lateral to the root-fibres of this nerve is still seen the 
descending root of the trigeminal nerve, with its nuclei, and 
ventral to the nucleus of the fourth nerve is the prominent 
medial longitudinal bundle. 

The formatio reticularis is traversed by numerous fibres 
froni the anterior peduncle of the cerebellum (brachium con- 
junctivum), which decussate in the raphe (decussatio brachii 
conjunctivi), and take a forward course to end in the ■ red 
nucleus, as we shall presently see. It will be noticed that the 
ventral fibres of the peduncle are the first to decussate. These 
ventral fibres are in reality not connected with the cerebellum, 
but form a commissure between the superior vestibular .nuclei 
of the two sides. 



Post col. 

NucW- ■^'^^"' ''' 

^-^-^ Zat.l 





Fig. 29. — Fo8t. col., Posterior colliculus. Aq. S., Aqueduct of Sylvius. 
D. r. T., Descending root of the trigeminal nerve and its nucleus. Lat. lem., 
Lateral lemniscus. A. p. c, Anterior peduncle of cerebellum. D. a. p. c, 
Decussation of anterior peduncle. - il/ed. lem., Medial lemniscus. Cen. nuc, 
Central nucleus. M. I. 6., Medial longitudinal bundle. ^X'nc. IV, Nucleus of 
the trochlear nerve. R. IV, Eoot-fibres of the trochlear nerve. G. p. c. Gray 
matter of posterior colliculus. 


Ventral to tlie peduncle is the medial lemniscns, still con- 
tinuous laterally with the lateral lemniscus. The latter tract 
has here a decided dorsal inclination, and terminates by aban- 
doning some of its fibres to the medial geniculate body through 
the posterior brachium, and others to the central gray matter, 
of the posterior colliculus — the nucleus of the posterior (in- 
ferior) colliculus (nucleus colliculi inferioris). Some of the 
cells of this nucleus send their axones forward to the anterior 
colliculus, while others enter the lateral lemniscus and pursue 
a posterior direction in that tract. 

The second section (Fig. 30) is through the anterior 
(superior) colliculi, and is entirely confined to the mesen- 

We have seen that the mesencephalon may be divided 
superficially into the corpora quadrigemina and the peduncles 
of the cerebrum. In sections each peduncle is divided into a 
dorsal portion — the tegmentum — and a ventral portion: the 
crusta, or base of the peduncle (basis pedunculi). The ground 
for this division is the substantia nigra, a mass of heavily-pig- 
mented cells, which appears, to the unaided eye, as a black 
streak across the section of the peduncle. The tegmentum is 
separated from the corpora quadrigemina by an arbitrary line 
drawn through the aqueduct. 

Taking up these parts separately, it will be seen that the 
fibres contained in the base of the peduncle are longitudinal 
in direction; they are derived from the cortex of the telen- 
cephalon, and we have seen most of them before as the pyram- 
idal tract and the cortico-pontile fibres. In the tegmentum 
dorsal to the substantia nigra is situated the reddish' mass of 
gray matter to which we have referred as the red' nucleus 
(nucleus ruber), in which terminates the anterior peduncle of 
the cerebellum after its decussation. Its medial margin is 
marked by the section of a small bundle of fibres, — the fascic- 
ulus retroflexus, — which connects the trigonum habenulse of 
the diencephalon with the ganglion interpedunculare : a mass 
of gray matter found between the beginning of the peduncles 
(not shown in the figure). 

Lateral to the red nucleus and dorsal to the lateral ex- 
tremity of the substantia nigra lies the lemniscus, its section 




Antcoi^'^- ^''^" Ac^S. 


- Nucmh. 

Fas. ret. 


Fig. 30.— An^. col.. Anterior colliculus. St. g., Stratum griseum. 
St. son., Stratum zonale. Aq. S., Aqueduct of Sylvius. Nuc. Ill, Nucleus 
of the oculomotor nerve. M. I. ft., Medial longitudinal bundle. Nuc. rub., 
Red nucleus. Fas. ret.. Fasciculus retroflexus. R. Ill, Root-fibres of the 
oculomotor nerve. Subs, nig., Substantia nigra. B. P., Base of peduncle. 
Lem., Lemniscus. St. al. p., Deep layer of white matter. 

64 THE anato:mt of the beaix. 

being somewliat comma-sliaped, with its small extremity point- 
ing dorsalward. In this situation the bundle gives off some 
fibres to the anterior eolliculus, but most of it is continued on 
to the diencephalon. 

Yentral to the aqueduct on each side of the median line 
is the very striking nucleus of the third cranial, or oculomotor, 
nerve (nervus oculomotorius) ; its root-fibres traverse the red 
nucleus and the substantia nigra, to emerge at the medial bor- 
der of the peduncle. It will be noticed that some of these 
fibres arise from the nucleus of the opposite side: i.e., the 
nerve undergoes a partial decussation. Immediately ventral 
to the nucleus of the third nerve is the section of the medial 
longitudinal bundle. 

The anterior colliculus is covered by a thin sheet of white 
matter, — the stratum zonale, — which consists, to a large ex- 
tent, of fibres from the optic tract on their way to terminate 
in the central gray matter of the colliculus (stratum griseum 
colliculi superioris). Limiting this gray stratum medially is 
another zone of white matter, — the deep white stratum 
(stratum album profundum), — which is composed of fibres 
that, arising from the cells of the gray stratum, curve around 
the aqueduct to enter the tegmentum and decussate in the 
raphe ventral to the medial longitudinal bundle. Many of 
them are believed to enter the medial longitudinal bundle and 
form a constituent part of it. The medial longitudinal bundle, 
then, consists, in part, of the axones of cells contained in the 
gray matter of the colliculi, in which, as we have seen, ter- 
minate fibres from the optic tracts and from the lemnisci. 
Now, the medial longitudinal bimdle in its course through 
the mesencephalon and the pons can be seen giving off fibres 
to the nuclei of the motor cranial nerves, especially those 
which innervate the ocular muscles. It is, therefore, not im- 
probable that this bundle is, to a large extent, a connecting 
tract between the corpora quadrigemina and the nuclei of 
motor cranial nerves, thus permitting certain reflex acts due 
to visual and acoustic impressions. Another source, however, 
for the fibres of this bundle is found farther forward in the 
mesencephalon in the shape of a small nucleus lateral to the 
aqueduct, and known as the nucleus of the medial longitudinal 
bundle (nucleus fasciculi longitudinalis medialis). 






Scp-peL .. 
Col.for.^' ~ 


H-nuchcaad'-. . 

! \ 

Ant com.- 

"; - - \ 'J^ 

T.nucl.caud.- - -l_ _ , 'f^ — _^w- 
Thai. '--~^-~~jM- 

St term — L_^ Wf / /, 

Paly, •., / ~^W / Ji 


Ant col .. 
Post col. 





■Mici. lent 
- Claus. 

... C.j.m. 
■ T.nucl.caud 


...Post, con 

Fig. 31. — For., Fornix. Sep. ftel., Septum pellucidum. Gol. for., Column 
of fornix. E. nucl. caud., Head of nucleus caudatus. Ant. com., Anterior 
commissure. T. nucl. caud., Tail of nucleus caudatus. Mas. int., Massa inter- 
media. Thai, Thalamus. St. term.. Stria terminalis. Pule, Pulvinar. Ant. 
col., Anterior colliculus. Post, col. Posterior colliculus. IT, Trochlear nerve. 
Ant. cor., Anterior cornu of lateral ventricle. A. I. int. cap., Anterior limb 
of internal capsule. Ext. cap.. External capsule. Jsh, Island of Reil. Nucl. 
lent.. Nucleus lentiformis. Glaus., Claustrum. P. I. int. cap., Posterior limb 
of internal capsule. Hipp., Hippocampus. Post, cor.. Posterior cornu of 
lateral ventricle. (After Landois.) 


In addition to tlie fibres derived from the medial longi- 
tudinal bundle numerous fibres enter tbe nuclei of the third 
and fourth cranial nerves; some of them are possibly fibres 
which have come down from the cortex of the telencephalon 
in the pyramidal tracts, and thus make connection between 
the cortex and the nuclei of these two nerves. 


The Thalamus. — The dorsal surface of the thalamus is 
white, owing to the presence of a thin stratum of fibres 
(stratum zonale) derived mostly from the optic tract. 

The medial surface is gray, and continuous with the gray 
matter lining the third ventricle and, through the massa in- 
termedia, with the opposite thalamus. 

The lateral surface of the thalamus is fused with the 
telencephalon. To appreciate this it is necessary to examine 
a horizontal section through the cerebram' (Fig. 31). Such 
a section discloses, in addition to the thalamus, two gray 
bodies, which, together, constitute the corpus striatum of the 
telencephalon; the anterior is the caudate nucleus, and the 
one lateral to the thalamus is the lentiform nucleus of the 
coi*pus striatum. The. thalamus and the corpus striatum are 
often called the "basal ganglia" of the cerebrum. The lenti- 
form nucleus is separated from the caudate nucleus and from 
the thalamus by an elbow-shaped layer of white matter: the 
internal capsule, consisting of two limbs, anterior and poste- 

A vertical transverse section through the thalamus (Fig. 
32) shows that it is composed of three nuclei more or less 
indistinctly separated by thin lamellee of white matter; they 
are distinguished as the lateral, medial, and anterior nuclei 
of the thalamus (nucleus lateralis, n. medialis, et n. anterior 
thalami). Some anatomists make another nucleus out of the 
ventral part of the lateral nucleus, and speak of it as. the 
ventral nucleus. From the cells in this latter portion of the 
thalamus arise numerous fibres, which, having passed through 
the posterior limb of the internal capsule, finally terminate 
in the cortex of the telencephalon ; they represent, as we shall 
see hereafter, the indirect continuation of the medial lemniscus. 



Nucicaud . 

fhsc thcilma/n. 

^ucl. ven.thaf. 


Corp- mo TV. | 

Tu6- cm. 


JViicl. lent? 

... Ant Com. 



Fig. 32. — 'Sucl. caud., Nucleus caudatus. Xucl. ant. thai., Anterior nu- 
cleus of thalamus. Fasc. thai, mam., Fasciculus thalamo-mamillari.s. Niicl. 
lat. thai.. Lateral nucleus of thalamus. Med. St., Medullaiy stria. Nucl. ven. 
thai., Ventral nucleus of thalamus. Xucl. vied, thai.. Medial nucleus of thala- 
mus. Int. cap.. Internal capsule. B. P. ent. cap.. Base of peduncle of cerebrum 
entering the internal capsule. Nucl. sub.. Nucleus hypothalamicus. B. P., 
Base of the peduncle of cerebrum. Col. for.. Column of fornix. Corp. mam., 
Corpus mamillare. Till), cin.. Tuber cinereum. Op. ch.. Optic chiasm. F. I. 
sup., Fasciculus longitudinalis superior. Island R., Island of Reil. Claus., 
Claustrum. Nncl. lent., Nucleus fentiformis. Ant. com., Anterior commissure. 
Op. tr., Optic tract. Nucl. amyg., Nucleus amygdala?. (After Edinger.) 


Another bundle of fibres, wliieh runs through the ante- 
rior limb of the internal capsule, connects the thalamus with 
the cortex of the telencephalon; about these not much is 
known, but it is held bv some that the thalamus is connected 
with every region of the cortex. 

The basal ganglia are connected with each other by fibres 
which run ventral to these bodies. 

The Hypothalamus. — Our knowledge of this region of 
the diencephalon is so imperfect that a very brief account will 
suffice here. The lamina terminalis and the tuber cinereum 
are composed of gray matter. The infundibulum is a diver- 
ticulum from the floor of the third ventricle to the hypophy- 
sis. The latter body is peculiar in that its two lobes are 
entirely different in structure; the posterior lobe contains 
nervous substance, while the anterior, being derived from the 
vault of the pharynx, consists of epithelial, tubules. 

The corpora mamillaria are gray internally (Fig. 32), and 
the gray matter in each is divided into three nuclei (nuclei 
corporis mamillaris). Each corpus receives the column of the 
fornix, as will be described hereafter, and is connected with 
the anterior nucleus of the thalamus by a bundle of fibres, the 
fasciculus thalamo-mamillaris of Yicq d'Azyr. 

Behind, the hypothalamus is fused with the peduncle of 
the cerebrum, the plane of fusion being commonly called the 
subthalamic region. A section through this (Fig. 33) shows, 
lateral td the red nucleus, a gray body not seen hitherto: the 
subthalamic nucleus (nucleus, hypothalamicus). The white 
matter dorsal to this nucleus consists largely of the fibres of 
the medial lemniscus. This tract terminates to a large extent 
in the ventral nucleus of the thalamus, from the cells of which 
run axones that continue the course of the lemniscus to the 
cortex of the telencephalon. Here we can also see the base 
of the peduncle continuous with the internal capsule. 

The Metathalamus.^ — The interior of the geniculate 
bodies is formed by gray matter known as their nuclei (nuclei 
corporis geniculati lateralis; n. c. g. medialis). The fibres of 
the optic tract terminate largely in the gray matter of the 
lateral geniculate body, but the tract also sends some fibres 
into the pulvinar of the thalamus, the anterior collic'ulus, and 



Corp. c^ J. 


Nucl. rned thai 
Nuclm I b. ..' 

J^ec/. nucl 

y5uL nig. 


-. Muclcaud, 
^ Nuclkhthdl 
--. In heap. 
. Zslcinc/. 
\Mici. ren. thcij, 

-.. Mec/J<2m, 
-- - Nuci.hypotn, 

Ant com. 
Tail vuclc^ud 

^ Temporal lohe. 

Fig. 33. — Corp. ml.. Corpus callosum. For., Fornix. Med. St., Medullary- 
stria. Niicl. med. thai., Medial nucleus of thalamus. Nucl. m. I. h., Nucleus 
of medial longitudinal bundle. Red nucl., Eed nucleus of the tegmentum. 
Svh. nig., Substantia nigra. B. P., Base of the cerebral peduncle. Nucl. 
caud., iSTucleus caudatus. N^icl. lat. thai.. Lateral nucleus of thalamus. Int. 
cap.. Internal capsule. Island, Island of Kiel. Nucl. ven. thai.. Ventral 
nucleus of thalamus. Med. lem., Region of the medial lemniscus. Nucl. 
hypoth., Nucleus hypothalamicus. Op. tr., Optic tract. Ant. com.. Anterior 
commissure. Tail niicl. caud.. Tail of nucleus caudatus. Hipp., Hippocam- 
pus. (After Edinger.) 


possibly into the medial geniculate body. Tlie latter body 
receives most of the lateral lemniscus. From the gray matter 
of the lateral geniculate body, the pulrinar, and the anterior 
colhculus spring fibres which run through the posterior limb 
of the internal capsule, continuing the course of the optic 
tract to the cortex and forming the so-called occipito-thalamic 
radiation of Gratiolet; while those from the medial genicu- 
late body continue the course of the lateral lemniscus to the 
cortex, terminating in the superior temporal convolution. 


If a horizontal section be made through the hemispheres 
just dorsal to the level of the corpus callosum (Fig. 34), there 
is brought to light in each hemisphere the appearance known 
as the centrum semiovale, or central mass .of white matter, 
dotted in the fresh specimen by sections of blood-vessels : the 
puncta vasculosa. The centrum is bordered by a thin con- 
voluted margin of gray matter: the cortex, or cortical sub- 
stance (substantia corticalis). . It can now be seen that each 
convolution consists of a central mound of white matter cov- 
ered by cortical substance. Moreover, the cortical substance 
lines even the deepest sulci, in the bottom and on the sides 
of which numerous small secondary convolutions are seen. 
The two centra semiovalia are connected by the broad band 
of white matter pre\'iously mentioned as the corpus callosum. 

The Corpus Oallosu:m. — rThis body should be studied 
in sagittal (Fig. 38), as well as in horizontal, sections of the, 
encephalon. It consists of a central portion, or trunk (trun- 
cus), and two extremities, anterior and posterior. The dorsal 
surface of the trunk presents on each side of the median line 
a slender longitudinal band, the nerve of Lancisi, or medial 
longitudinal stria (stria longitudinalis medialis) ; and laterally 
at the junction with the centrum a similar band, the lateral 
longitudinal stHa (stria longitudinalis lateralis). Between the 
two strife stretches an exceedingly delicate gray lamella: the 
fasciola cinerea. 

The ventral surface of the trunk is concave, and forms 
the roof for a cavity in each hemisphere: the lateral ventricle. 



Fig. 34. — G., Genu of corpus callosum. >S'/)Z., Splenium of corpus eallosum. 
St. I. I., Lateral longitudinal stria. St. I. m., Medial longitudinal stria. F. c, 
Pasciola cinerea. C, Cortex. Gen. sem., Centrum semiovale. (After Eauber.) 


The posterior extremity is thickened, and is called the 

The anterior extremity is the knee (genu); here the 
corpus callosum makes a ventral bend, which is continued 
backward under the name of rostrum. The longitudinal striae 
accompany it in this course, and under the name of peduncle 
of the corpus callosum, or gyrus subcallosus, pass to the ante- 
rior extremity of the hippocampal convolution, as previously 

The great bulk of the fibres of the corpus callosum are 
transverse in direction : they radiate into the centra semiovalia 
in all directions, going to almost all parts of the cortex. They 
belong to the class of commissural fibres: i.e., they connect 
corresponding parts of the two hemispheres. 

The Lateral Ventricles. — The lateral ventricle (ven- 
triculus lateralis) of each hemisphere may be, exposed by carry- 
ing an antero-posterior incision through the corpus callosum 
on each side of the median line, and severing the attachments 
of that body in front, behind, and laterally. It is a wide and 
shallow cavity divided into a central portion (pars centralis) 
and three prolongations, or horns (cornua). 

The anterior horn (cornu anterius) is directed forward 
and lateralward into the substance of the frontal lobe. 

The posterior horn (cornu posterius) runs backward, 
lateralward, and then medialward into the substance of the 
occipital lobe; it is marked by a ridge thrown up by the cal- 
carine fissure: the calcar avis. 

The middle, or inferior, horn (cornu inferius) curves 
posterior and ventral to the thalamus, winding backward, 
lateralward, ventralward, forward, and medialward into the 
temporal lobe nearly to its anterior extremity. In its floor is 
a ridge, produced by the dentate fissure, following the course 
of the horn throughout its length, and called Ammon's horn, 
or the hippocampiis. / 

Keturning to the central portion of the ventricle, its roof 
is formed by the corpus callosum. Its lateral wall is formed 
by the junction of the corpus callosum with the white matter 
of the hemisphere. In its floor are seen the following objects, 
starting at the lateral wall and proceeding toward the median 




[nFFr. coni^ 


■ Fi'ssyl 
... 0}}c)C.^reQ, 
I. Cl&us. 

Fig. 35. — Corip. ml., Corpus callosum. Atit. com., Anterior commissure. 
Inf. Fr. conv., Inferior frontal convolution. Ext. cap., External capsule. 
Isl. R., Island of Reil. Fis. syl., Fissure of Sylvius. Olfac. area, Olfactory- 
area. Clans., Claustrum. C. n., Caudate nucleus. Int. cap., Internal capsule. 
Gl. p., Globus pallidus. P., Putamen. (After Edinger.) 


line : A large gourd-shaped mass of gray matter, — the caudate 
nucleus of the corpus striatum; then the stria terminalis and 
vena terminalis; then the lateral half of the dorsal surface 
of the thalamus; next a fringe of blood-vessels rolled in pia 
mater; the chorioid plexus (plexus chorioideus) of the lateral 
ventricle ; and, finally, one-half of a triangular sheet of white 
matter, the fornix, which has a half in each lateral ventricle. 
We shall now study each of these objects separately. 

The Corpus Striatum. — To obtain a satisfactory concep- 
tion of the corpus striatum and the neighboring parts of the 
hemisphere it is necessary to examine a series of transverse 
and horizontal sections of this region (Figs. 31, 32, 33, 35, 
and 36), from which we learn the following facts: The corpus 
striatum contains two distinct collections of gray matter, one 
of which is seen in the floor of the ventricle, while the other 
is imbedded in the white matter lateral to the ventricle. The 
intraventricular portion is the caudate nucleus (nucleus cau- 
datus); it begins with an enlarged anterior extremity, — the 
head (caput), — and rapidly tapers backward to a long, narrow 
column: the tail (cauda). The tail first arches backward, run- 
ning dorsal and then lateral to the thalamus; it then turns 
forward ventral and lateral to the thalamus, and can be traced 
in transverse sections along the roof of the inferior horn of 
the ventricle to a thickened portion of the cortex in the ante- 
rior extremity of the temporal lobe: the amygdaloid, or 
almond-shaped, nucleus (nucleus amygdalae). 

The extraventricular part of the corpus striatum is called 
from its shape the lentiform nucleus (nucleus lentiformis). 
It lies in a plane lateral and posterior to the caudate nucleus, 
from which it is separated by a narrow sheet of white matter: 
the anterior limb of the internal capsule. On its medial side 
is the thalamus, which, however, extends farther backward 
than the lentiform nucleus; from this it is separated by the 
posterior limb of the internal capsule. In transverse sections 
it is seen that the lentiform nucleus is composed of three 
divisions separated from each other by thin planes of white 
matter; the lateral and highest of these divisions is called the 
putamen, while the other two constitute the globus pallidus. 
Lateral to the nucleus lentiformis is a sheet of white matter 


Corp. cal 





Ant. ^" 

Genu int.Cctp' 

Olf-ac &rea. 

Fig. 36. — Corp. cal., Corpus callosum. Nticl. caiul., Nucleus caudatus. 
Ch. pi, Chorioid plexus. NticJ. ant. thai., Anterior nucleus of thalamus. 
Nucl. med. thai, Medial nucleus of thalamus. Col for., Column of the 
fornix. Int. cap., Internal capsule. Gl jxil, Globus pallidus. A7it. com., 
Anterior commissure. Olf. tr., Olfactory tract. Fasc. long, sup., Superior 
longitudinal bundle. Genu int. cap., Genu of internal capsule. Isl, Island 
of Eeil. Clam., Claustrum. Pvt., Putamen. Fasc. ttncin., Fasciculus un- 
cinatus. Olfac. area. Olfactory ai=ea. (After Edinger.) 


known as tlie external capsule, and bordering this laterally is 
a thin layer of gray matter, the claustrum, which is continuous 
ventrally with the amygdaloid nucleus; still farther lateral 
we recognize the convolutions of the island of Eeil. 

The Internal Capsule. — The internal capsule (capsula 
interna) is the plane of white matter situated between the 
head of the caudate nucleus and the thalamus as the medial 
boundary, and the lentiform nucleus as the lateral boundary. 
It may be divided into two limbs, or portions: an anterior 
(pars frontalis) and a posterior (pars occipitalis). The former 
is contained between the head of the caudate nucleus and the 
lentiform nucleus, the latter between the lentiform nucleus 
and the thalamus. The two limbs meet at an obtuse angle, 
opening laterally, their point of junction forming the knee 
(genu) of the internal capsule. Through this narrow space 
pass the fibres which connect the cortex of the hemisphere with 
the lower-lying parts of the brain. The anterior hmb consists 
of fibres which connect the thalamus with the cortex; the 
anterior two-thirds of the posterior limb contain fibres which 
conduct impulses to the motor nuclei of the pons and of the 
peripheral nerves, — i.e., motor fibres, — while through the 
posterior one-third of this limb pass fibres which convey im- 
pulses from the peripheral nerves to the cortex: i.e., sensory 

The amygdaloid nucleus, previously mentioned, is a thick- 
ened portion of the cortex of the temporal lobe: it receives 
the stria terminaHs, and is continuous with the claustrum and 
with the tail of the caudate nucleus. 

The Fornix and the Hippocampus.- — -The fornix is 
formed by two cords which are triangular on cross-section, 
with the bases facing each other, the thin edges looking 
lateralward. These cords diverge behind, converge in front; 
the diverging portions are connected with each other and with 
the ventral surface of the corpus callosum by transverse fibres 
known as the lyra (commissura hippocampi). Owing to these 
fibres, the fornix appears triangular, with its apex forward and 
its base backward. At the apex of the fornix, about midway 
between the two extremities of the corpus callosum, the cords 
separate, and, under the name of columns of the fornix (col- 


rase- Dent 

In f- con 




Fig. ST.— Inf. cor., Inferior liorn of lateral ventricle. Hipp., Hippocam- 
pus. Fasc. Dent, Dentate fascia. Dent, fiss., Dentate fissure. Hipp, conv., 
Hippocampal convolution. Fimb., Fimbria. (After Edinger.) 


umnas fomicis), run toward the liypotlialaums to terminate in 
the corpora niamillaria. Anterior to them as they diverge can 
be seen the transverse band called the anterior commissure 
(commissura anterior cerebri). Between the column of the 
fornix and the anterior tubercle of the thalamus on each side 
is the opening of a Y-shaped canal connecting the third with 
the lateral ventricles; it is called the foramen of Monro. 
From the point where the fornix ceases to be adherent to the 
ventral surface of the corpus callosum by means of the lyra 
appears a new structure, — the septum pellucidum, — forming 
the dividing wall between the lateral ventricles. On section 
it is found to consist of two laminae separated by a very nar- 
row cavity: the ca\Tim septi pellucidi. 

Posteriorly, each cord of the fornix, under the name of 
crus, enters the inferior horn of the ventricle, where it be- 
comes continuous Avith the hippocampus, and takes the name 
of fimbria ; it is accompanied by the chorioid plexus from the 
central portion of the ventricle. 

To examine the hippocampus a horizontal section should 
be made through the region of the inferior horn (Fig. 37). 
It will be seen that the hippocampus is a ridge thrown up by 
the dentate fissure on the medial surface of the hemisphere, 
and that it is continuous with the hippocampal convolution 
(Fig. 38). In other words, it is an infolded portion of the 
cortex. Both gray and white matter are folded, but the white 
ceases s'ooner than the gray, which, continuing, bends first 
lateralward and then toward the median line, to terminate in 
a free edge, which, because of its serrated appearance, is 
known as the dentate fascia (fascia dentata). It is not in the 
cavity of the lateral ventricle, but is continuous over the 
posterior extremity of the corpus callosum Avith the fasciola 
cinerea and the longitudinal stria, and through them with the 
gyrus subcallosus. All these structures — fascia dentata, fas- 
ciola cinerea, longitudinal strife, and gyrus subcallosus— may 
be considered as a rudimentary, or "aborted," convolution, and 
together represent the free edge of the cortex of the hem- 

Many of the axones of the cells of the hippocampus enter 
the fimbria of the fornix, whence some of them -cross the 




i^^<^E_. GMChl. 


Ant. com. , 


Fig. 38. — G., Genu of corpus callosum. Eep. pel., Septum pellucidum. 
Corp. cal., Corpus callosum. Snl. C. C, Sulcus of corpus callosum. Gy. cin., 
Gyrus cinguli. Spl., Splenium of corpus callosum. P. for., Crus of fornix. 
Fas. den., Fascia dentata. Fiml)., Fimbria. Hip. conv., Hippocampal con- 
volution. Unc, Uncus. Col. for., Column of fornix Ant. com.. Anterior 
commissure. L. t., Lamina terminalis. (After Van Gehuchten.) 


median line in the lyra to enter the fimbria of the opposite 
side and end in the liippocampus. Others continue forward 
in the fornix to the column, by which most of them are con- 
ducted to the corpus mamillare; but some enter the septum 
pellucidum and pass to the uncus of the hippocampal con- 
volution, while still others probably turn backward in front of 
the foramen of Monro, and run through the stria meduUaris 
of the thalamus to the trigonum habenulae. 

The Chorioid Plexus, Velum Interpositum, and Trans- 
verse Fissure. — To the unaided eye both the chorioid plexus 
and the lateral half of the dorsal surface of the thalamus ap- 
pear to lie in the floor of the lateral ventricle. As a matter 
of fact, both are outside of that cavity, being covered dorsally 
by a layer of epithelium passing between the free edge of the 
fornix and the stria terminalis. Just as we saw in the study 
of the fourth ventricle that the dorsal wall of the rhomben- 
cephalon ceases to form nervous tissue along a line corre- 
sponding to the free edge of the posterior medullary velum, 
so here, along a line corresponding to the free edge of the 
fornix all the way from the foramen of Monro to the termina- 
tion of the fimbria in the inferior horn, the dorsal wall of the 
telencephalon ceases to lay down nervous tissue, and stretches 
in its primitive epithelial state over the chorioid plexus and 
the thalamus to the stria terminalis, Avhere, again, nervous 
tissue — i.e., the diencephalon — is developed. As it passes 
over the plexus and the lateral half of the dorsal surface of 
the thalamus it becomes firmly attached to these structures. 
At the edge of the fornix and at the stria terminalis it is con- 
tinuous with the general ependymal epithelium of the ven- 

If the fornix be cut across near its apex and turned back- 
ward (Fig. 39), there is exposed the triangular flap of pia 
mater called the velum interpositum (tela chorioidea ven- 
triculi tertii). Its apex is forward just behind the apex of the 
fornix, while its sides, which are elevated into the vascular 
tufts which we have called the chorioid plexuses, project be- 
yond the edge of the fornix, and invaginate the epithelium 
both in the central portion and in the inferior horns of the 
ventricle. It is composed of two layers. Bearing in mind 




_- Jfucl Caud 


Fig. 39. — St. term., Stria terminalis. Thai., Thalamus. Hipp., Hippo- 
campus. Fimh., Fimbria. Aiit. cor., Anterior cornu of lateral ventricle. Kticl. 
cavd.. Nucleus caudatus. Col. for., Columns of the fornix. Tel. int.. Velum 
interpositum. Ch. pi., Chorioid plexus. C'al. av., Calcar avis. Post, eor., 
Posterior cornii of lateral ventricfe. (After Gray.) 


that tlie liemisplieres in tlie embryo undergo great growth in 
the posterior direction and that the pia mater closely invests 
the surfaces of the encephalon, it will be understood that in 
the course of development two layers of the pia, one covering 
the dorsal wall of the telencephalon and the other that of the 
diencephalon, Avould be early brought together, and caught, 
as it were, between these two growing vesicles. The space 
through which the velum enters the cerebrum is the trans- 
verse fissure of Bichat (fissura transversa cerebri). It may be 
compared to a horseshoe in shape, the dentate fissures furnish- 
ing the lateral arms of the shoe, while the cross-bar is the 
space between the posterior extremity of the corpus callosum 
dorsally and the pineal body and the mesencephalon ventrally. 
It is not a fissure in the sense of a cleft opening into the 
lateral ventricles, for, as we follow the space toward these 
cavities, we find that its bottom is closed by the epithelium 
before described as extending between the edge of the fornix 
and the stria terminalis, and investing the chorioid plexuses 
and the lateral half of the dorsal surface of the thalamus. 

The ventral surface of the velum is adherent to the epi- 
thelial roof of the third ventricle, which constitutes its lamina 
epithelialis. Between this epithelium and the pia there runs, 
in an antero-posterior direction, on each side of the median 
line the chorioid plexus of the third ventricle. 

The Anterior Co^imissure. — This band of fibres has 
been referred to as running transversely in front of the col- 
umns of the fornix. As it is- chiefly concerned with the con- 
nections of the rhinencephalon, it will be considered later. 

The White Matter oe the Pallium. — The pallium is 
the name given to the gray cortex and the central white 
matter. The latter may be divided into three classes of fibres 
as follow^s: — 

(A) Fibres of association, or those which connect two 
parts of the same hemisphere. Of these there are two' sets : 
the long and the short. The latter are all those innumerable 
fibres which connect neighboring points of the cortex (fibrse 
proprise). The long connect two or more lobes, and are ar- 
ranged in four fairly distinct bundles (Fig. 40) : — 

1. The superior longitudinal bundle (fasciculus longi- 


Fib. .prop- 


Fig. 40.— Scheme of fibres of association of cerebral hemisphere (after 
Van Gehuchten). Fih. prop., Fibres proprise. F. Long, sup., Fasciculus longi- 
tudinalis superior. F. Long, inf., Fasciculus longitudinalis inferior. Cing., 
Cingulum. F. itncif., Fasciculus uncinatus. 


tudinalis superior), which conuects the frontal with the occip- 
ital and temporal lobes. 

2. The inferior longitudinal bundle (fasciculus longi- 
tudinalis inferior), connecting the occipital and temporal 

3. The cingulum, which arches in the gyrus cinguli from 
the frontal to the temporal lobe. 

4. The uncinate bundle (fasciculus uncinatus), uniting 
the ventral frontal convolution with the uncus of the tem- 
poral lobe. 

(B) Commissural fibres, or those which connect convo- 
lutions in one hemisphere with corresponding convolutions in 
the other, such as the corpus callosum and the lyra (com- 
missura hippocampi). 

(C) Projection-fibres, or those Avhich connect the cortex 
with lower-lying portions of the central nervous system. 
These, as we have seen, pass through the internal capsule; 
their radiation from the cortex to the capsule is called the 
corona radiata. They are of such importance that a separate 
chapter will be devoted to them. 

The Ehinekcephalox. — There are many deficiencies in 
our knowledge of the rhinencephalon, but the following state- 
ments seem warranted at present. The principal constituents 
of the olfactory bulb are the numerous large cells around 
whose dendrites the fibres of the olfactory nerves terminate. 
These cells send their axones backward to form the olfactory 
tract; on arriving at the trigonum, they separate into two 
roots, or striae. The medial root ends in the trigonum and 
the gyrus subcallosus. The lateral root enters the uncus of 
the hippocampal convolution, where most of its axones ter- 
minate; but some after crossing in the anterior commissure 
turn forward into the lateral stria and tract of the opposite 
side, to end in the bulb. The anterior extremity of the hippo- 
campal convolution is connected with the hippocampal eon- 
volution of the opposite side by the anterior commissure, and 
with the hippocampus of the same side by fibres running in 
the fornix, as already described. The hippocampus, in its 
turn, is connected by the column of the fornix with the cor- 
pus mamillare, by the stria medullaris with the trigonum 


liabenulas, and by the lyra with the hippocampus of the op- 
posite side. In man the olfactory apparatus must be regarded 
as, to a large extent, rudimentary, but from analogy with cer- 
tain of the lower animals in whom the apparatus receives full 
development, there seems no doubt that the entire gyrus 
fornicatus, the hippocampus, the fornix, the anterior com- 
missure, the fascia dentata, and the fasciola cinerea are all 
concerned with the sense of smell. 


The Coxducting-patiis of the E^•CEPHALOx. 

The cortex of each hemisphere of the telencephahjn is 
in communication with the opposite half of the body by means 
of fibres conducting impulses to and from it. These fibres 
may be divided into two sets, according to the direction of 
conduction: centrifugal, or motor, which conduct excitations 
from the cortex to the various muscles of the body; and cen- 
tripetal, or sensory, which convey excitations from the skin, 
mucous membranes, bones, special sense-organs, etc., to the 
cortex, Avliere are produced in an unknown way what we call 
sensations. Each half of the body is thus represented in or 
projected upon the cortex of the opposite hemisphere; hence 
the name of '^projection-fibres" given to those fibres of the 
telencephalon through which the communication is main- 
tained. They are in many instances collected into distinct 
bundles; so that we may speak of motor and sensory paths 
or tracts, meaning thereby definite groups of fibres along 
which motor or sensory impulses, as the case may be, habit- 
ually travel. Moreover, these groups of fibres often arise from 
or terminate in fairly-definite areas of the cortex, which areas 
are usually called centres. Thus, that area from which spring 
the fibres that conduct impulses to the muscles which produce 
the movements of the hand may be called the motor '^centre" 
of the hand ; that which receives the fibres along which visual 
impressions travel is the "centre" of sight. 

The Principal Motor Path. — This path is formed by 
two groups of neurones. The cell-bodies of the first group 
are contained in the cortex, and their axones terminate in the 
nuclei of the motor peripheral nerves on the opposite side of 
the nervous axis, — in the mesencephalon, pons, medulla, and- 
spinal cord,— where they enter into conduction-relation with 
the second group of neurones, whose medullated axones con- 
stitute the motor peripheral nerves. We are directly con- 
cerned in this place onlv with the first, or cortical, neurones. 



Their cell-bodies are found in the cortex of the convolutions 
around the central sulcus of Rolando: the anterior central 
convolution and the posterior extremities of the other frontal 
convolutions, the posterior central convolution, and the para- 
central lobule, which collectively are called the "motor area" 
of the cortex. In a general way, we may say that the ventral 
portion of this area is the motor centre for the head, the mid- 
dle portion that for the upper extremity, and the dorsal por- 
tion that for the lower extremity. The axones of the cells in 
this area converge toward the internal capsule, and pass 
through the anterior two-thirds of its posterior limb. In the 
capsule the fibres destined to reach the nuclei of the facial and 
hypoglossal nerves occupy the genu, and hence are called the 
geniculate fasciculus. Posterior to them are the fibres for 
the upper extremity, and behind these are those for the lower 
extremity (Fig. 31). From the capsule the fibres of this path 
enter the base of the peduncle of the cerebrum; here the 
geniculate fasciculus occupies the medial border of the pe- 
duncle, while the other fibres of the path lie in the middle of 
that structure. In the mesencephalon, it will be recalled, are 
the nuclei of the third and fourth cranial nerves; they prob- 
ably receive fibres from this path, but neither the cortical 
origin nor the course of such fibres is known. 

From the peduncle the path reaches the pons, where some 
of its fibres cross the median line to terminate in the nuclei 
of the motor nerves there found. jSText, the path appears in 
the medulla as the pyramid, for which reason it is frequently 
called the pyramidal tract throughout its extent. In this re- 
gion fibres are distributed to the motor nuclei of the ninth, 
tenth, eleventh, and twelfth cranial nerves, chiefly of the 
opposite side. At the spinal extremity of the medulla the 
majority of the fibres cross to the lateral column of the op- 
posite side of the spinal cord, in which they constitute the 
crossed pyramidal tract (fasciculus cerebro-spinalis lateralis), 
which traverses the whole length of the cord, abandoning 
fibres to the ventral horn as it goes, thus making connection 
with the spinal lower motor neurones. The small part of the 
tract which does not cross in the medulla at the decussation 
forms the direct pyramidal tract (fasciculus cerebro-spinalis 


anterior) in tlie ventral column of the cord, whence its fibres, 
in large part, cross successively in the ventral white com- 
missure, to end in the ventral horn of the opposite side. 

The Secondary Motor Path. — There exists an anatom- 
ical basis for a second motor path from the cortex of the tel- 
encephalon to the motor nuclei of the peripheral nerves, 
though it cannot be traced with the same distinctness as the 
preceding, nor is much known concerning its function. It is 
formed by at least four groups of neurones, three of which are 
in the encephalon. The cells of the cortical neurones lie in the 
same area as those of the principal path, and also in the cor- 
tex of the temporal lobe. They send their axones through the 
anterior two-thirds of the posterior limb of the internal cap- 
sule, whence they enter the base of the peduncle of the cere- 
brum. Here those which arise in the "motor area" occupy 
the same position with the principal motor path, while those 
which arise in the temporal lobe lie in the lateral part of the 
peduncle (Fig. 41). All these fibres terminate in the nuclei 
pontis; whence the name of cortico-pontile given to them. 
The cells of the nuclei pontis^ which are the second group of 
neurones, send their axones across the median line to enter the 
cerebellar hemisphere and terminate around Purkinje's cells 
in the cortex. These Purkinje cells constitute the third group 
of iTeurones, but the course pursued by their axones is unde- 
cided; there is good reason for believing that they reach the 
ventral horn of the spinal cord, either directly or indirectly 
through the olive. 

The Principal Sensory Path. — The portions of each 
half of the spinal cord believed to conduct the various Centrip- 
etal impressions from the skin, muscles, and viscera are the 
funiculi of GoU and Burdach, and the ventro-lateral ground- 
bundle. The latter of these is formed by fibres which spring 
from cells in the gray matter of the opposite side of the cord, 
while the two funiculi first mentioned contain the central 
axones of the ganglia on the dorsal roots of the spinal nerves 
of the same side. It will be recalled that the ventro-lateral 
ground-bundle on reaching the medulla lies dorsal to the 
pyramid, and that the two dorsal funiculi of the cord ter- 
minate in their respective nuclei, the cells of which send axones 



Fig. 41. — /, Eegion of temporo-pontile fibres. //, Region of pyramidal 
tracts. ///, Eegion of geniculate fasciculus. S. n., Substantia nigra. (After 


across the median line as internal arcnate fibres, to enter first 
the interolivary layer and later the medial lemniscus. This 
medial lemniscus is the principal sensory path in the enceph- 
alon. We have traced it through the medulla, where it lies 
medial to the olive and lateral to the raphe; thence into the 
pons, where it becomes flattened and lies dorsal to the deep 
transverse fibres; and thence into the tegmentum of the mes- 
encephalon, where it fuses laterally with the lateral lemniscus. 
In its course through the rhombencephalon it is joined by 
fibres derived from the terminal nuclei of the sensory nerves 
there found; these, as we have seen, constitute many of the 
internal arcuate fibres, and join the lemniscus of the opposite 
side from that in which they arise. The axones from the nuclei 
of the cochlear nerve, however, have a separate path. From 
the mesencephalon the medial lemniscus enters the dienceph- 
alon, where the majority, at least, of its fibres end in the ventral 
nucleus of the thalamus. Here are the cells of the last group 
of neurones, whose axones pass through the posterior third 
of the posterior limb of the internal capsule to terminate in 
the cortex of the telencephalon over an area — the somsesthetic 
area — which practically coincides with that which we have 
termed the motor area. It will be noticed that this path, like 
the principal motor path, is crossed. It is formed by three 
superimposed groups of neurones as follows: (1) the periph- 
eral, whose peripheral axones form the peripheral sensory 
nerves and whose central axones build up the dorsal funiculi 
of the cord; (2) the spinal and rhombencephalic, whose axones 
form, respectively, the ventrb-lateral ground-bundle of the 
cord and the internal arcuate fibres and medial lemniscus ; and 
(3) the thalamo-cortical, whose axones complete the connection 
with the cortex. 

The Secok^daey Sensory Path. — As in the case of motor 
impulses, so, for the sensory, there exists the anatomical basis 
of a complex secondary path. The two cerebellar tracts from 
the cord — the direct cerebellar tract and the main mass of 
Gowers's tract — terminate in the cerebellum ; moreover, some 
of the sensory cranial nerves, notably the trigeminal and the 
vestibular portion of the acoustic, send some fibres into the 
cerebellum, as do also the terminal nuclei of the dorsal fu- 


niciili of the cord. Thus there are numerous fibres conduct- 
ing centripetallj as regards tlie cerebellum. From the latter 
fibres run in the anterior peduncle to the. red nucleus of the 
mesencephalon on the opposite side; the red nucleus sends 
fibres into the thalamus of the same side, and from the thal- 
amus, as we have seen, many fibres proceed to the cortex. So 
that it seems quite possible that certain sensory impressions 
may reach the cortex by this roundabout path. 

The Acoustic Path. — The path traveled by auditory 
impressions is composed of four groups of neurones. The cen- 
tral axones of the peripheral neurones form the cochlear portion 
of the acoustic nerve, which terminates in the two gray masses 
known as the dorsal and ventral nuclei of the cochlear nerve. 
These two nuclei contain the cells of the second group of neu- 
rones. Those of the ventral nucleus send their axones into the 
pons, to form the trapezoid body. The fibres of this body 
undergo a partial decussation, some of them terminating in 
the anterior olive of the same side, while others cross the 
raphe to reach the anterior olive of the opposite side. This 
olive furnishes the third group of neurones; their axones run 
forward, and, aided, perhaps, by the acoustic striae from the 
dorsal nucleus of the opposite side, form the lateral lemniscus, 
which ends in the medial geniculate body and in the posterior 
colliculus. In these two bodies the fourth group of neurones 
is found; their axones enter the posterior third of the poste- 
rior limb of the internal capsule, and terminate in the dorsal 
(superior) convolution of the temporal lobe. It should be 
borne in mind that the acoustic path is only partially crossed, 
since the trapezoid body only partially decussates; in other 
words, each dorsal temporal convolution is in communication 
with both ears. 

The Optic Path. — In this path there are three sets of 
neurones. The cells of the first set are contained in the retina ; 
they are the bipolar cells of this membrane. The cell-bodies 
of the second set are also found in the retina; they are the 
so-called ganglion-cells of the retina; their axones run back- 
ward and medialwarcl as the optic nerve to enter the chiasm. 
In the chiasm the optic nerve partially decussates. The usual 
statement is that the nerve undergoes a semidecussation, in 


process of wliicli the fibres from the temporal half of the 
retina emerge from the chiasm as the lateral half of the optic 
tract of the same side, while the fibres of the medial half of 
the tract are derived frora the medial half of the opposite 
retina. However, anatomical investigation has thus far not 
been able to establish anything mnch more definite than that 
a partial decussation occurs in the chiasm. The optic tract, 
formed thus by fibres from both retinae, runs backward and 
lateralward, winding first ventral and then lateral to the cere- 
bral peduncle, to gain the diencephalon, where its fibres ter- 
minate in the lateral geniculate body, the pulvinar of the 
thalamus, and the anterior colliculus of the mesencephalon. 
In the gray matter of these structures are the cell-bodies of 
the third group of optic neurones. Their axones, having en- 
tered the posterior third of the posterior limb of the internal 
capsule, turn backward, run through the occipito-thalamic 
radiation, and terminate in the cortex of the cuneus, espe- 
cially in the vicinity of the calcarine fissure. 

It seems established that the optic tract and nerve also 
contain fibres which conduct centrif ugally : i.e., fibres which 
run from the lateral geniculate body, anterior colliculus, and 
thalamus to the retina?. 

The Olfactory Path. — This path is constituted of two 
sets^f neurones. The axones of the peripheral set, the olfac- 
tory nerves, terminate in the bulb, where the cells of the 
second, or central, set are situated. The axones of these are 
directed backward as the olfactory tract, which divides into 
the two olfactory roots, or strise. The medial stria ends in 
the olfactory trigonum, the gyrus subcallosus, and the ad- 
jacent portion of the gyrus fornicatus; the lateral stria ter- 
minates in the hippocampal convolution, especially in the 
neighborhood of its uncus. Hence these areas of the cortex 
may be considered olfactory centres. From them proceed 
paths which throw the lower motor neurones under the in- 
fluence of the sense of smell, thus accounting for olfactory 


Ala cinerea, 10, 4G. 

Aqueduct of Sylvius, 4, 19, 60. 

Area, parolfactoi'ia. 33. 

the acoustic, 10, 12, 46. 
Axis, the neural, 1. 

Basis pedunculi, 62. 

Body, the pituitary, 22. 

Brachium quadrigeminum inferius, 18. 

"superius, 18. 
Bulb, the olfactory, 33. 

Calamus scriptorius, 8. 

Calear avis^ 72. 

Canal, the central, of medulla, 40. 

the neural, 1. 
Capsule, the external, 76. 

the internal, 66, 74, 76. 
Centrum semiovale, 70. 
Cerebellum, 2. 

connections of, 58, 59. 

internal anatomy of, 58. 

surface anatomy of, 12. 
Cerebrum. 4, 24. 
Chiasm, the optic, 20, 22. 
Cingulum, 24. 
Claustrum, 76. 
Clava, 8. 
Colliculus, facialis, 12. 

inferior, 18. 

internal anatomy of, 64. 

superior, 18. 
Columns of fornix, 78. 
Commissure, anterior, of cerebrum, 78. 

of the habenulae, 21. 

of the hippocampus, 76. 

posterior, of the cerebrum, 21. 
Convolution or convolutions, angular. 

ascending frontal (precentral) , 26. 

ascending parietal (postcentral), 

calloso-marginal, 32. 

fusiform, 28. 

hippocampal. 30, 32. 

inferior frontal, 26. 

inferior temporal, 28. 

middle frontal. 26. 

middle temporal, 28. 

Convolution or convolutions, occipital, 

of corpus callosum, 30. 

orbital, 26. 

straight, 26. 

superior frontal, 26. 

superior temporal, 28. 

supramarginal, 28. 
Corpora quadrigemina, 2, 18, 62. 
Corpus callosum, 24, 70, 72. 

geniculatum laterale, 20, 70. 
mediale, 20, 70. 

mamillare, 22, 68. 

pineale, 21. 

restiforme, 8, 18, 46. 

striatum, 24J 66, 74. 

trapezoideum, 48, 52. 
Crura of fornix, 78. 
Cuneus, 30. 

Decussation of anterior peduncles of 
cerebellum, 60. 

of lemnisci, 38. 

of optic nerves, 91. 

of pyramids, 6, 36. 
Diencephalon, 2. 

intei'nal anatomy of, 66. 

surface anatomy of, 19. 

Eminentia medialis, 12. 
Encephalon, the divisions of, 1, 2. 
Ependymal epithelium, 2. 
Epithalamus, 4. 

surface anatomy of, 21. 

Fascia dentata, 78. 

Fasciculi longitudinales of pons Va- 
rolii, 50. 
Fasciculus, inferior longitudinal. 84. 

medial longitudinal, 42, 46, 56, 64. 

retroflexus. 62. 

superior longitudinal, 82. 

thalamo-mamillaris, 68. 

uncinatus, 84. 
Fasciola cinerea, 70. 78. 
Fibres, association of telencephalon. 

cerebello-olivary, 40, 46. 

commissural of telencephalon. 84. 

cortico-pontile, 56. 

external arcuate. 46. 




Fibre?, internal arcuate, 38, 40, 44. 

projection of telencephalon. 84. 

transverse of pons Varolii, 50. 
Fissure, ealcarine. 30. 

collateral. 30. 

dentate, 30. 72. 

dorsal median, 8. 

horizontal, 14. 

longitudinal, of cerebrum. 24. 

of Sylvius. 24. 

paramedian, 8. 

parieto-occipital. 25, 30. 

transverse of Bichat. 82. 

transverse of cerebellum. 14. 

ventral median, 6. 
Flocculus, 14. 
Foramen, of ]Magendie, 16. 

of ]Monro, 76. 
Formatio reticularis, 36. 
Fornix, 76. 
Fossa interpeduneularis, 18. 

rhomboidea. 8, 15. 
Fovea inferior. 18. 

superior. 18. 
Frenulum, 18. 
Funiculus of Burdach. 8. 

of GoU, 18. 

Ganglion interpedunculare, 62. 
Globus pallidus. 74. 
Gyri transitivi, 26. 
Gyrus, fornieatus. 32. ^ 

subcallosus. 33. 72. 

HabenuJa. 21. 

Hemispheres of telencephalon. 24. 

lateral surface of. 24. 

medial surface of. 30. 
Hippocampus.' 72, 78. 
Hypophysis, 22. 
Hypothalamus, 4. 14. 

internal anatomy of, 68. 

surface anatomy of. 22. 

Incisure, dorsal, of cerebellum. 14. 

ventral, of cerebellum, 14. 
Infundibulum. 22. 68. 
Island of Eeil. 25, 30, 76. 

Lamina, chorioidea epithelialis. 16. 

terminalis. 22. 68. 
Lemniscus, the lateral, 10, 56, 62. 

the medial, 38, 52, 56. 
Lingula. 14. 
Lobe, frontal. 24, 26. 

limbic, of Broca. 32. 

occipital. 24. 30! 

parietal. 24. 28. 

temporal. 24. 28. 

Lobes of cerebelh;m. 14. 
Lobule, inferior parietal, 28. 

paracentral, 32. 

superior parietal, 28. 
Locus cceruleus. 12. 
Lyra, 76, 80. 

Mesencephalon, 2. 

internal anatomy, 60. 

surface anatomy, 18. 
Met^ncephalon, 2. 

internal anatomy, 48. 

surface anatomy, 10. 
Myelencephalon, 2. 

internal anatomy, 34. 

surface anatomy, 6. 

Xerve, abducens, 8. 

acoustic, 8, 46. 

cochlear. 48. 

facial, 8'. 

glosso- pharyngeal, 6. 

hypoglossal, 6. 

oculomotor. 64. 

optic. 20. 91. 

spinal accessory, 6, 34. 

trigeminal. 10. 54. 

trochlear, 60. 

vagus, 6. 

vestibular, 48. 
Xidus a^^s, 14. 
Xodulus, 14. 
Nucleus or nuclei, ambiguus, 42. 

amygdaloid. 74. 76. 

caudatus. 66. 74. 

central, of pons Varolii, 54. 

dentatus. 58. 

dorsal of cochlear nerve, 46. 

emboliformis, 58. 

fastigii, 58. 

globosus. 58. 

hypothalamicus. 68. 

lentiformis. 66, 74. 

of abducens nerve, 52. 

of Bechterew, 50. 

of Deiters, 50. 

of facial nen^e. 50. 52. 

of funiculus of Burdach, 38. 

of funiculus of Goll. 38. 

of giosso-pharyngeal nerve. '42. 

of .hypoglossa:i nerve, 42. 

of lateral lemniscus. 56. 

of oculomotor nerve, 64. 

of olive, 40. 

of spinal accessory nerve, 34. 

of thalamus. 66. 

of tractus solitarius. 42. 

of trigeminal nerve, 54. 



Xucleus or neuclei, of trochlear nerve, 
54, 60. 
of vagus nerve, 42. 
of vestibular nerve, 48. 
jjontis, 50. 
red, 59, 60, 62. 
superior olivary, 52. 
ventral of cochlear nerve, 48. 

Olive, 6. 
Operculum, 25, 30. 

Pallium, 24, 82. 

Path, conducting, 85, 86. 

acoustic, 91. 

olfactory, 92. 

optic, 91. 

principal motor, 86. 

principal sensory, 88. 

secondary motor, 88. 

secondary sensory, 90. 
Peduncle, anterior, of cerebellum (bra- 
chium conjunctivum). 10, 
18, 52. 

middle, of cerebellum (brachium 
pontis) , 10. 

of cerebrum, 2, 18. 
Plexus, chorioid, of fourth ventricle, 16. 

of lateral ventricle, 78, 80. 

of third ventricle, 82. 
Pons Varolii, 2. 

internal anatomy of, 48. 

surface anatomy of, 10. 
Process, inferior vermiform, 14. 

superior vermiform, 14. 
Prosencephalon, 2. 
Pulvinar, 19. 
Putamen, 74. 
Pyramid, of medulla oblongata, 6. 

Radiation, occipito-thalamic. 70. 
Raphe, 38. 
Recess, lateral, 15. 

of infundibulum, 22. 

optic, 18. 

Rhinencephalon, 24. 

internal anatomy of, 85, 86. 

sui'face anatomy of, 32. 
Rhombencephalon, 2. 

isthmus of, 2, 15. 
Root, descending of trigeminal ner/e, 

descending of vestibular nerve, 40, 
Root-fibres, of abducens nerve, 52. 

of acoustic nerve, 46. 

of cochlear nerve, 46. 

of facial nerve, 52. 

Root-fibres, of oculomotor nerve, 64. 
of trigeminal nerve, 54. 
of trochlear ner^-e, 60. 
of vestibular nerA'e, 46. 

Septum pellucidum, 78. 

Stratum interolivare lemnisci. 42. 

Stria or strise, acoustic, 8, 46. 

lateral longitudinal, 70. 

medial longitudinal, 70. 

medullaris, 19. 

olfactory, 33. 

terminalis, 19. 
Sulcus, basilaris, 10. 

calloso-marginal. 32. 

central, of Rolando, 25. 

chorioid. 19. 

circularis, 30. 

dorso-lateral, 6. 

inferior frontal, 26. 

inferior temporal, 28. 

interbrachialis, 18. 

interparietal, 28. 

lateralis, 19. 

liraitans, 10, 12. 

marginal, 32. 

median longitudinal, 8, 12. 

middle temporal, 28. 

of corpus callosum, 30. 

of Monro, 19. 

olfactory, 26, 33. 

post-central, 26. 

precentral, 26. 

subfrontal, 32. 

subparietal. 32. 

superior frontal, 26. 

superior temporal, 28. 

ventrolateral. 6. 
Substantia, corticalis, 70. 

gelatinosa, 34. 

nigra, 62. 

perforata anterior, 24. 33. 

perforata posterior, 18. 

Tegmentum. 62. 

Tela chorioidea, of third ventricle, 21, 

of fourth ventricle, 16. 
Telencephalon, 2. 

internal anatomy of. 70. 

surface anatomv of, 24. 
Tent, 14. 

Thalamencephalon. 4. 
Thalamus, internal anatomy of, 66. 

surface anatomy of, 19. 
Tract, crossed pyramidal, 36. 

direct cerebellar. 40. 



Tract, direct pyramidal, 36. 

lateral, 6. 

of Gowers, 40, 59. 

olfactory, 33. 

optic, 19, 20, 22, 68. 

solitary, 42, 44. 

spinalj'^of trigeminal nerve, 34 
Trigonum, habenulse, 19, 21. 

hypoglossal, 10, 46. 

olfactory, 33. 
Tuber cinereum, 22, 68. 
Tubercle, anterior, of thalamus, 20. 

cuneate, 8. 

Vallecula, 14. 
Valve of Vieussens, 12. 
Velum, anterior medullary, 12, 

interpositum, 80. 

posterior medullary, 14. 
Vena terminalis, 19. 
Ventricle, fourth. 3, 15, 16. 

third, 4, 21. 

lateral, 4, 72. 

Worm. 14. 

14, 18, 


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