. WILLIAMSON,

SAN FRANCISCD £

MEDICAL # LIBRARY

Wo.

John Marshall Williamson
Memorial

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QUAIN'S • *

ELEMENTS OF ANATOMY

EDITED BY

EDWARD ALBERT SCHAFER, F.R.S.

PROFESSOR OF PHYSIOLOGY AND HISTOLOGY IN UNIVERSITY COLLEGE, LONDON,

AND

GEORGE DANCER THANE,

PROFESSOR OF ANATOMY IN UNIVERSITY COLLEGE, LONDON.

IN THREE VOLUMES.

VOL. III.— PART I.
THE SPINAL CORD AND BRAIN.

BY PROFESSOR SCHAFER.
ILLUSTRATED BY 139 ENGRAVINGS.

Cent!)

"LONDON:
LONGMANS, GREEN, AND CO.

AND NEW YORK: 15 EAST 16th STREET.
1893.

LONDON
BKADBUKY, AGNEW, & CO. LD., PRINTERS WHITEFRIARS.

CONTENTS OF PAET I.

THE SPINAL CORD AND BRAIN.

PAGE

THE CEREBRO-SPINAL Axis . . . i
THE SPINAL COED . . . . .2

External form . .... 2

Fissures . . . . . . 6

Internal structure . . . . . 7

Grey Matter ..... 7

Central Canal 9

White Matter ..... 9

Features of different regions . . . 10

Microscopic structure . . . .12

General structure 12

Distribution of Nerve-Cells • . .14
of Anterior Horn . . . . 14

of Clarke's Column . . .16

of Middle Cell- Column . . . 17

of Posterior Horn ; Solitary Cells. 17

Commissures . . . . . . 18

Central Canal . . . . . . IQ

Origin of Spinal Nerves . . . .

Anterior Roots *'f

Posterior Roots '. . . . .

Collateral Fibres ....

Conducting Tracts .....

Methods of investigation
Antero-lateral Column . . . .

Posterior Column ....

Degenerations in Spinal Cord . . .
From section of Posterior Roots .
From Lesions of the Brain . . .,
From Lesions of the Cerebellum .
From Lesions of the Cord . . .
THE BRAIN OR ENCEPHALON .
THE MEDULLA OBLONGATA AND PONS
VAROLII ......

THE MEDULLA OBLONGATA

External characters .....

Posterior Area .....

Lateral Area . . . ...

Olivary Body . .

Anterior Area ......

Pyramids . . . . . - .

THE PONS VAROLII

19
19

20

21
22
22
24
26
27
27

31

32
32
38

38
38
38

43
45
45
45
45
46

Fourth Ventricle 47

Internal structure of Medulla Oblongata 5 1

Closed part . . . . . 5 1

Ventricular part 53

Nucleus of Olivary Body . . .56

Formatio Reticularis . . . . 58

Arched Fibres 59

Internal structure of Pons Varolii . . 60
Course of Fibres from Cord through Bulb

and Pons 63

Transition from Pons to Mid-Brain . . 65

THE CEREBELLUM 69

External form . . . . . . 69

Upper surface . . . . . 71

Under surface . . . . . . 74

Arbor Vitaj 83

Commissural Fibres in White Matter . 84

Peduncles .84

Microscopic structure . . 86

Degenerations following Lesions of. . 93

THK MID-BRAIN AND INTER-BRAIN . . 96

Aqueduct of Sylvius . . . -96

Third Ventricle 97

Central Grey Matter of Aqueduct . . 98
Crura Cerebri . . . . . . 100

Crusta ...... 100

Substantia Nigra . . . . . 101

Tegmentum . . . . .102

Tract of Fillet 103

Dorsal part of Mid-Brain . . . 105
Corpora Quadrigemina . . . . 105
Posterior Commissure .... 109

Geniculate Bodies 109

Optic Thalami no

Trigonum Habenulse . . . . 113
Subthalamic Tegmental Region . .114

Pineal Body 114

Posterior Perforated Space . . .115
Corpora A Ibicantia . . . . 115

Infundibulum, and Tuber Cinereum . 116
Pituitary Body . . .' . . 116
Lamina Cinerea . . - . . 1 1 7
Optic Tracts and Chiasma . . .117
THE LATERAL VENTRICLES : CORPORA

STRIATA : CEREBRAL HEMISPHERES 122
Lateral Ventricles . . . . .122

Corpus Callosum . . . . . 127

Septum Lucidum . v . . .129
Fornix . . . . . . . 129

Tsenia Semicircularis . . .. .131

Corpora Striata . . . . . . . . 131

External Capsule 135

Claustrum . . . . . . 135

Internal Capsule . . . . 136

Cerebral Hemispheres . . . . 137

External form . . . . . 137

Fissures 141

Frontal Lobe 145

Parietal Lobe 149

Occipital Lobe 151

Temporal Lobe 152

Central Lobe or Island of Reil . . 154

Limbic Lobe 155

Olfactory Lobe . . . . . 159

28G'!

IV

CONTENTS OF PART I.

PAGE

THE CEREBRAL HEMISPHERES — continued.
Variations in Fissures and Convolu-
tions 161

Causation of Gyri and Sulci . . . 162
Structure of White Matter . . -163
Structure of Grey Matter . . . 166
Differences of structure in different
parts . . . . . . 172

MEASUREMENTS OF THE BRAIN . . . 176

Dimensions . . . , 176

Extent of Grey Cortex . • »'„'-. • 176
Thickness of Cortex . . . .177
Weight 178

PAGE

MEMBRANES OF BRAIN AND SPINAL CORD 181

Dura Mater 181

Subdural space . ^ . . . . 184

Pia Mater 184

Arachnoid Membrane . . . . 187
Subarachnoid Space . . . .187
Ligamentum Denticulatum . . . 189
Glandulae Pacchionii . . . .190

BLOOD-VESSELS OF BRAIN AND SPINAL

CORD . . . . . . 191

Spinal Cord . '. . . . .191

Brain ....... 193

LYMPH-PATHS OF BRAIN AND SPINAL CORD 198

NEUBOLOGY.

THE CEREBRO-SPINAL AXIS.

By E. A. SCHAFER.

THE cerebro- spinal axis is divided into the
brain or encephalon, the enlarged part within the
skull, and the spinal cord within the vertebral
canal. It is symmetrical in form, consisting of
a right and a left half, separated to some extent
by fissures and cavities, but united by various
portions of white and grey nervous substance
which cross from one side to the other, and

Fig. 1.-

-VlEW OF THE CEREBRO-SPINAL AXIS.

Bourgery. ) i

(After

The right half of the cranium and trunk of the body
has been removed by a vertical section ; the membranes of
the right side of the brain and spinal cord have been cleared
-away, and the roots and first part of the fifth and twelfth
cranial nerves, and of all the spinal nerves of the right
side, have been dissected out and laid separately on the
wall of the skull and on the several vertebraa opposite to
the place of their natural exit from the cranio-spinal cavity.

F, T, 0, frontal, temporal and occipital lobes of cere-
brum ; C, cerebellum ; P, pens Varolii ; m o, medulla
oblongata ; m s, m s, point to the upper and lower
extremities of the spinal marrow ; c e, on the last lumbar
vertebral spine, marks the cauda equina ; v, the three
principal branches of the nervus trigeminus ; C i, the
sub-occipital or first cervical nerve ; C vm, the eighth or
lowest cervical nerve ; D i, the first dorsal nerve ; D xn,
the last dorsal ; L i, the first lumbar nerve ; L v, the last
lumbar ; S i, the first sacral nerve ; S v, the fifth ; Co I,
the coccygeal nerve ; s, the left sacral plexus.

form the commissures of the brain and spinal
cord.

The cerebro-spinal axis is enveloped within
the skull and vertebral canal by three connective
tissue membranes, between which are spaces
occupied by a clear fluid (cerebro-spinal fluid).
These envelopes, which will be described later,
are, 1st, a firm fibrous membrane named the
dura mater, which is placed most externally ;
2nd, a delicate membrane called the arachnoid ;
and, 3rd, a highly vascular membrane named the
pia mater, which is next to, and closely invests
the surface of the brain and cord.

VOL. III.

THE SPINAL CORD.

SPINAL CORD.

The spinal cord or spinal marrow (medulla spinalis) is about 18 inches (45
centimeters) long, and extends from the margin of the foramen magnum of the occi-
pital bone to about the lower part of the body of the first lumbar vertebra. Above,
it is continued into the bulb (medulla oblongata) ; below, it tapers conically and
ends in a slender filament, the ftlum terminate or central ligament of the spinal cord.

Although the cord usually ends near the lower border of the body of the first
lumbar vertebra, its termination is sometimes a little above or below that point, as

Fig. 2. — SECTIONS SHOWING THE GENERAL RELATIONS OF THE SPINAL CORD TO THE INCLOSING THECA,

AND OF THIS TO THE VERTEBRAL CANAL. (Key and Retzius.)

A, through the fifth cervical vertebra ; B, through the tenth dorsal vertebra ; C, through the first
lumbar vertebra and the foramen of exit of the twelfth dorsal nerve-roots ; D, through the disk between
the second and third lumbar vertebrae ; E, through the first sacral vertebra. In A, B, and C, the cord,
covered by pia mater, is seen in the centre, with the ligamentum denticulatum attached to it on either
side ; the nerve-roots on either side form small groups which, since they pass obliquely downwards to
their foramina of exit, are cut across ; the dura matral sheath is separated by a considerable space from
the cord, and by a quantity of loose areolar and fatty tissue from the wall of the vertebral canal. This
tissue is in smaller amount in C. D and E are below the termination of the cord, and show sections of
the nerve-bundles of the cauda equina within the dural sheath, which is very large in D, but compara-
tively small in E, the vertebral canal in the latter being largely occupied by adipose tissue. In this are
seen the sections of two large veins. The arachnoid is not represented in any of these sections.

opposite to the last dorsal or to the second lumbar vertebra. The position of the
lower end of the cord also varies according to the state of curvature of the vertebral
column, in the flexion forwards of which the end of the cord is slightly raised. In
the foetus, at an early period, the embryonic cord occupies the whole length of the
vertebral canal ; but, after the third month, the canal and the roots of the lumbar
and sacral nerves begin to grow more rapidly than the cord itself, so that at birth the
lower end reaches only to the third lumbar vertebra. After birth the thoracic part
of the cord lengthens proportionately more than the other parts, so that in the infant
the roots of the lower dorsal nerves come off relati velv higher up than at a later age
(Pfitzner).

THECA. 3

The cord is enclosed in the vertebral canal within a sheath (theca) considerably
longer and larger than itself, formed by the dura mater, and separated from the walls
of the canal by venous plexuses, and much loose areolar tissue (fig. 2). The cavity of
the sheath between the pia mater and the dura mater is occupied by cerebro-spinal
fluid, and is divided by the curtain-like arachnoid into the spaces, subdural and sub-
arachnoid, above mentioned. Within the latter the cord, covered closely by pia
mater, is suspended, being kept in position by a ligament on each side (ligamentum
denticulatum), which fixes it at frequent intervals to its sheath, and by the roots of
the spinal nerves which pass across the space from the surface of the cord towards
the intervertebral foramina.

The spinal nerves come off in pairs at intervals along the cord. The portion
of spinal cord to which each pair of roots is attached is termed a " segment," but
there is in man and mammals complete continuity from segment to segment, and
not even a sign of constriction between them. Each nerve is attached to the surface
of the cord by two roots, one of which is anterior or ventral and non-gangliated,1 the
other is posterior or dorsal and is provided with a ganglion. The uppermost two
or three nerve-roots cross the subarachnoid and subdural spaces nearly horizontally
(figs. 1 and 5), but the rest pass across with a more and more oblique downward
inclination until their direction is almost vertical, and indeed the lower part of the
theca below the termination of the cord (fig. 2, D, E), is occupied by the descending
roots of the lumbar and sacral nerves, passing to the foramina between the corre-
sponding vertebrae. This mass of nerve-roots, which conceals the delicate fihun
terminale, is named the cauda equina (figs. 4, 5, 6).

The relation between the spines of the vertebras and the places of attachment of
the nerve-roots to the cord is illustrated by the appended diagram (fig. 3) from
Reid, which is founded upon observations made on six adult subjects. From this it
will be seen that there is a much larger amount of variation than might have been
supposed. This is especially the case with the dorsal nerve-roots, some of which
show variations of their position of origin extending over a distance covered by as
many as three spinous processes. Certain general facts can, however, be made out
which are not without practical interest. Amongst these are the position of the
second cervical nerve — opposite the arch of the atlas ; that of the first dorsal or
thoracic nerve, opposite the sixth or seventh cervical spine ; that of the seventh
thoracic nerve, opposite the fourth or fifth dorsal spines, and of the sacral nerves, the
range of which extends from the eleventh dorsal to the first lumbar spine. The
line of origin of the sacral nerves very nearly corresponds in vertical extent with the
body of the first lumbar vertebra.

No doubt this variation is largely accounted for by the variations in length and
obliquity of the spinous processes of the vertebrae, and accordingly we find that
there is least fluctuation of relative position at the top and bottom of the series.
The anterior and posterior (ventral and dorsal) nerve-roots belonging to the same
segment of the cord leave it practically at the same level (Reid).

The cervical enlargement (see next page) about corresponds in vertical extent
with the spines of the cervical vertebras, while the lumbar enlargement corresponds
with the spines of the tenth, eleventh, and twelfth thoracic and the interval between
the last named and the first lumbar.

In section the cord is nearly circular, especially in the thoracic region, but it is
somewhat flattened before and behind. In the thoracic region, it measures about
ten millimeters (0'4 inch) from side to side, and about eight from before back. The

1 Some animals (e.g. , cat) have a few ganglion-cells interpolated amongst the fibres of the anterior or
ventral nerve-roots. Hoche finds that in the anterior roots of the lower lumbar and sacral nerves of
man, just at their junction with the cord, ganglion-cells, like those of the posterior root, are almost
constantly present, lying singly or in groups, and connected with some of the issuing nerve-fibres by a
T-shaped junction.

B 2

THE SPINAL CORD.
A
111

•»T" CERVICAL

.3RD DORSAL

8T" DORSALS

IO™ DORSAL <

>1|TM DORSAL

2NO LUMBAR <

\-7 C

9~

Fig. 3. — DIAGRAM SHOWING THR

VARYING RELATIONS OF THE ROOT-
ORIGINS OF THE SPINAL NERVES
TO THE SPINES OF THE VERTEBRA!.

(After K. W. Reid.)

Fig. 4. — A, VENTRAL (ANTERIOR) AND B, DORSAL (POSTERIOR) VIEWS OP THE MEDULLA OBLONGATA AND
SPINAL CORD WITH SECTIONS. (Allen Thomson. ) \

The cord has been divested of its membranes and of the roots of the nerves. The filiform prolonga-
tion, represented separately in B', has been removed. C, a transverse section through the middle of the

EXTERNAL FORM.

medulla oblongata ; D, a section through the middle of the
cervical enlargement of the cord ; E, through the upper
dorsal region ; F, through the lower dorsal region ; G, through
the middle of the lumbar enlargement ; and H, near the lower
end of the conus medullaris.

1 to 6 refer to parts of the medulla oblongata ; the
remaining numbers to parts of the spinal cord.

1, pyramids ; 1', their decussation ; 2, olivary bodies ;
3, lateral columns ; 4, fourth ventricle ; 4', calamus scrip-
torius ; 5, funiculus gracilis ; 6, funiculus cuneatus ; 7,
7, anterior median fissure of the spinal cord ; 8, 8, postero-
lateral groove corresponding to the attachments of the pos-
terior nerve-roots ; 9, 9, posterior median fissure ; x , taper-
ing extremity of the cord ; x , x , in B', filum terminale.

cord is not, however, of uniform diameter
throughout, but is swollen out in the cervical
and lower dorsal regions, two enlargements
being thereby produced — an upper or cervical
(brachial), and a lower or lumbar (crural) (fig. 4).
Of these the cervical enlargement is of greater
size and extent than the lumbar. It extends from
the upper limit of the cord to the body of the first
or second thoracic vertebra ; it is largest oppo-
site the fifth or sixth cervical vertebra, where it
measures from 13 to 14 mm. from side to side.
The lower or lumbar enlargement begins at the
tenth thoracic vertebra, is largest opposite the
twelfth (11 — 13 mm. across), and from this
point becomes gradually smaller ; its antero-pos-
terior diameter is more nearly equal to the

Fig. 5. — DIAGRAMMATIC VIEW FROM BEFORE OF THE SPINAL

CORD AND MEDULLA OBLONGATA, INCLUDING THE ROOTS
OF THE SPINAL AND SOME OF THE CRANIAL NERVES, AND
ON ONE SIDE, THE GANGLIATED CHAIN OF THE SYMPA-
THETIC. (Allen Thomson.) {.

The spinal nerves are enumerated in order on the right
side of the figure. Br, brachial plexus ; Cr, anterior
crural, 0, obturator, and Sc, great sciatic nerves, coming
off from lumbo-sacral plexus ; x , x , filum terminale.

a, 6, c, superior, middle and inferior cervical ganglia of
the sympathetic, the last united with the first thoracic,
d ; d', the eleventh thoracic ganglion ; I, the twelfth
thoracic (or first lumbar) ; below s s, the chain of sacral
ganglia.

transverse than is the case in the cervical en-
largement. Below the lumbar enlargement the
cord tapers in the form of a cone (conus medul-
laris'), from the apex of which the small fili-
form prolongation is continued downwards.

The cervical and lumbar enlargements have
an evident relation to the large size of the
nerves which supply the upper and lower limbs,
and which are connected with those regions of
the cord. At the commencement of its develop-
ment in the embryo the spinal cord is destitute

of these enlargements, which, in their first appearance and subsequent progress,
correspond with the growth of the limbs.

The terminal filament (filum terminale, central ligament) (fig. 6, 5, V) descends

6

THE SPINAL CORD.

in the middle line amongst the nerves composing the cauda equina, and, reaching
the lower end of the sheath opposite to the second sacral vertebra, perforates the dura
mater, and receiving an investment from it, passes on to be attached with this to the
periosteum of the lower end of the sacral canal, or to the back of the coccyx. It is
a prolongation of the pia mater, enclosing for about half its length an enlarged
continuation of the central canal of the cord (see p. 9), with a little grey matter
near the upper end. Below the termination of the canal, the filum is mainly com-
posed of connective tissue, with blood-vessels prolonged
from the anterior spinal vessels, and on either side there
run in it three or four small bundles of medullated nerve-
fibres, some of which" have a few ganglion-cells. These
nerve-bundles are regarded by Rauber as representing
rudimentary coccygeal nerve-roots. They have no con-
nection with the coccygeal nerves proper.

The filum terminale is distinguished by its silvery
hue from the nerves among which it lies.

Fig. 6. VlEW FROM BEHIND OF THK LOWER END OF THE SPINAL

COED WITH THE CAUDA EQUINA AND DUKAL SHEATH. (Allen

Thomson.) \

The sheath has been opened from behind and stretched towards
the sides ; on the left side all the roots of the nerves are entire ; on
the right side both roots of the first and second lumbar nerves are entire,
while the rest have been divided close to the place of their passage
through the sheath. The bones of the coccyx are sketched in their
natural relative position to show the place of the filum terminale
and the lowest nerves.

a, placed on the posterior median fissure at the middle of the
lumbar enlargement of the cord ; b, b. the terminal filament, drawn
slightly aside by a hook at its middle, and descending within the
dural sheath ; 6', b', its prolongation beyond the sheath and upon
the back of the coccygeal bones ; c, the dural sheath ; d, double
foramina in this for the separate passage of the ventral and dorsal
(anterior and posterior) roots of each of the nerves ; e, ligamentum
denticulatum ; Dx, and DXII, the tenth and twelfth thoracic (dorsal)
nerves ; Li, and Lv, the first and fifth lumbar nerves ; Si, and Sv,
the first and fifth sacral nerves ; Ci, the coccygeal nerve.

Fissures. — The spinal cord is incompletely divided
into a right and left half by two fissures which pass in
from the middle of the anterior and posterior surfaces,
and penetrate through the greater part of its thickness.
Of these two median fissures the anterior or ventral (fig.
7, 1) is wider and therefore more distinct than the pos-
terior or dorsal, although it does not, in most parts,
penetrate to more than one-third the thickness of the
cord, while the posterior fissure may reach more than
half-way from back to front. The anterior contains a
fold of the pia mater and also many blood-vessels, which
are thus conducted to the centre of the cord. At the
bottom of this fissure is a transverse connecting portion
of white substance named the anterior or white com-
missure.

The posterior (fig. 7, 2) is not an actual fissure, for,
although the lateral halves of the cord are quite separate
dorsally, there is not so much a fold of the pia mater between them, as merely a
of connective tissue and blood-vessels prolonged from that membrane which

INTERNAL STRUCTURE. ?

passes in nearly to the centre of the cord (posterior septum"). Its position is marked,
especially in the lumbar enlargement and in the cervical region, by a superficial
furrow. At its end is the posterior or grey commissure.

Besides these two median fissures, a lateral furrow is seen on each side of the cord,
corresponding with the line of attachment of the posterior roots of the spinal nerves.
It is named the postero-lateral groove (fig. 7, C, 4). Each lateral half of the cord is

Fig. 7. — DIFFERENT VIEWS OF A PORTION

OF THE SPINAL CORD FROM THE
CERVICAL REGION WITH THE ROOTS

OP THE NERVES. Slightly enlarged.
(Allen Thomson.)

In A, the anterior or ventral surface
of the specimen is shown, the anterior
nerve-root of the right side having been
divided ; in B, a view of the right side is
given ; in C, the upper surface is shown ;
in D, the nerve-roots and ganglion are
shown from below. 1, the anterior
median fissure ; 2, posterior median
fissure ; 3, antero-lateral impression,
over which the bundles of the anterior
nerve-root are seen to spread (this im-
pression is too distinct in the figure) : 4,
postero-lateral groove into which the
bundles of the posterior root are seen to
sink ; 5, anterior root ; 5', in A, the
anterior root divided and turned up-
wards ; 6, the posterior root, the fibres
of which pass into the ganglion, 6' ; 7,
the united or compound nerve ; 7', the
posterior primary branch, seen in A and
D to be derived in part from the ante-
rior and in part from the posterior root.

divided superficially by the postero-lateral groove into a posterior and an antero-
lateral part. The attachment of the anterior roots, however, subdivides the latter
into anterior and lateral portions.

An antero-lateral groove has sometimes been described in the line of origin of the anterior
roots of the nerves, but usually has no real existence. The fibres of these roots in fact,
unlike the posterior, do not dip into the spinal cord in one narrow line, but spread over a
space of some breadth.

On the posterior surface of the cord, at least in the upper part, there is on each
side of the middle line a slightly marked longitudinal furrow (fig. 11) situated about
one millimeter from the posterior median fissure, and marking off, in the cervical
region, a slender tract, the postero-mesial column. This sulcus, which is better
marked in some individuals than in others, is termed the posterior intermediate
furrow. An incomplete connective tissue septum (posterior intermediate septum)
extends from the furrow into the white substance of the cord. The larger remaining
part of the posterior column is termed the postero-lateral column.

INTERNAL STRUCTURE OF THE SPINAL CORD: RELATIVE PROPORTIONS OP GREY

AND WHITE MATTER.

Grey matter. — When the spinal cord is cut across (figs. 8, 11, 14) it is seen that
the grey matter occupies the more central parts, being almost completely enclosed by
the white matter. The grey matter appears in the form of two irregularly crescentic
portions on either side, united across the middle line by the posterior grey commis-
sure before mentioned, so that its section may be compared in shape to the letter H.

8

THE SPINAL CORD.

The concave side of each lateral crescent faces outward, and in consequence of the
depth of the posterior median fissure the commissure of grey matter joins the crescents
nearer their anterior than their posterior ends, except in the lumbar region of the cord.
The two horns or cornua of each crescent are named from their position anterior
and posterior (or, better, ventral and dorsal) ; the anterior or ventral horn (fig. 8,
a. c) is the shorter and broader, and is everywhere separated from the surface of the
cord by white matter which is traversed by the bundles of the anterior roots at the
part where these enter the cord. The posterior or dorsal horn (p. c} is longer and
narrower, and tapers almost to a point (apex cornu posterioris), which closely

Fig. 8. — SECTION OF THE SPINAL CORD IN THE UPPER PART OF

THE DORSAL REGION. (E. A. S. ) \

a, anterior median fissure ; p, posterior-median fissure ; p, n,
posterior nerve-roots entering at the postero- lateral groove ; a, c,
anterior cornu of grey matter ; p, c, posterior cornu ; i, inter-
medio-lateral tract (lateral cornu) ; p, r, processus reticularis ; c,
posterior vesicular column of Clarke ; «, pia-matral septum form-
ing the lateral boundary of the postero-mesial column.

approaches the external surface of the cord at the
postero-lateral groove, with which it is connected

by a process of the superficial neuroglia which here dips in towards the horn,
but is interrupted by a stratum of fine nerve-fibres known as the marginal
bundle. The posterior horn is slightly narrowed at its base (cervix cornu} ; from
that place it gradually expands into the main part of the horn (caput cornu), and
from this it tapers in the way just noticed. Near its tip the caput cornu has a
peculiar semi-transparent aspect, an appearance due to the siibsiantia gelatinosa of
Eolando (fig. 14), which forms a kind of cap to the cornu. The part of the grey
crescent between the two horns is known as the intermediate grey substance (Gowers).

Near the middle of the outer surface of each crescent the grey matter is less
sharply marked off than elsewhere from the white matter ; portions of grey matter
extending into the lateral white column and uniting with one another into what in
sections appear like a network enclosing portions of white substance (p. r.). This is
known as the processus reticularis ; it is best marked in the cervical region (fig. 14).
At the postero-lateral part of the anterior horn, immediately in front of the
processus reticularis, the grey matter forms in the upper dorsal (thoracic) region
(fig. 11, Dl) a somewhat pointed triangular projection, which is sometimes distin-
guished as the lateral horn but is better known as the intermedio-lateral tract of
Lockhart Clarke (intermediate process of Gowers) (fig. 8, i). Above, in the cervical
region, this blends with and forms part of the enlarged anterior horn. This is
also the case in the lumbar enlargement, but in the sacral region the lateral horn
again becomes distinct.

The grey crescents vary in form in different parts of the cord (see fig. 9). In
the dorsal (thoracic) region both anterior and posterior cornua are narrow. In the
cervical and lumbar regions the anterior cornua are large and broad. The posterior
cornua are narrow in the cervical and thoracic, but very broad in the lumbar region.
The grey matter is seen in a series of sections to be most abundant in the lumbar
region of the cord, and least in the thoracic.

It is clear that what appear in section as irregular crescentic areas of grey matter
are in reality long irregularly fluted columns, and that the commissural band uniting
the convex edge of the crescents is a flattened expansion, connecting the columns
along their whole length. But it is both customary and convenient to speak of the
various parts of the grey matter of the cord according to their appearance in sections,
•although the term " columns" is very generally applied to what appear in section

INTERNAL STRUCTURE.

9

as groups of nerve-cells, occurring in different parts of the grey matter, as well as
to the several portions of the white matter immediately to be described.

Central canal. — Extending through the whole length of the spinal cord, in the
substance of the grey commissure, there is a minute canal (fig. 8) which, in sections
of the cord, is barely visible as a speck, with the naked eye. It is continued above
into the medulla oblongata, where it gradually approaches the posterior surface and
eventually opens out at the calamus scriptorius of the fourth
ventricle. At the lower end of the cord, near the extremity
of the conus medullaris, it becomes enlarged, and shaped like
the letter ~|~, and is stated by some observers to open on the
dorsal or posterior surface of the cord ; but this is denied by
others. This central canal, though minute, is an object of
considerable interest as a typical part of the structure of the
cord, since it is the permanent remains of the epiblastic canal
from which the spinal cord is developed. It is more distinct
in lower vertebrata than in mammals.

White matter. — The white substance of each half of the cord completely
encloses the grey matter except opposite the posterior horn. This last therefore
serves to separate off a smaller posterior white column, which is somewhat wedge-
shaped in section and is bounded internally by the posterior median fissure, from the

Fig. 9. — SECTION OF

THE SPINAL CORD
NEAR THE EXTRE-
MITY OF THE CONUS

MEDULLARIS. Mag-
nified about six dia-
meters.

Pig. 10. — DIAGRAM SHOWING BOTH THE ABSOLUTE AND RELATIVE EXTENT OF THE GREY MATTER AND

OF THE WHITE COLUMNS IN SUCCESSIVE SECTIONAL AREAS OF THE SPINAL CORD, AS WELL AS THE

SECTIONAL AREAS OF THE SEVERAL ENTERING NERVE-ROOTS (adapted from Ludwig and Woroschiloff).

(E. A. S.)

The sectional areas of the several entering nerve-roots (n.r) as well as the extent of the grey matter
{gr), and of the lateral, posterior, and anterior columns of white matter (I, c., p. c., and a. c.}, are
represented in superposed curves, the common abscissa of which (abs.) is intersected at equal intervals
by as many ordinates as there are pairs of spinal nerves. In the ordinates each millimeter above the
abscissa represents about one square millimeter of sectional area.

rest of the white substance which forms a large antero-lateral while column (figs. 7
to 9). The antero-lateral column is sometimes arbitrarily divided into anterior and
lateral white columns, the place of passage of the bundles of the anterior nerve-roots
being taken as the limit between the two ; but since these are scattered over a
considerable part of the transverse section it is clear that the limit cannot be
distinctly fixed.

The white substance is traversed by imperfect septa of connective tissue
prolonged inwards from the pia mater. Most of these are irregular and somewhat
variable in position, with the exception of one in the cervical region extending
inwards towards the grey commissure from the sulcus before described as bounding
the postero-mesial column. This, the posterior intermediate septum before men-
tioned (p. 7) (fig. 8, s) cuts off a small portion of the posterior column next to the
posterior median fissure, corresponding to the projection of the postero-mesial column
on the surface.

10 , THE SPINAL COED.

The lateral symmetry of the spinal cord is not always perfect. The white columns
especially are found slightly to vary, the variation being generally caused by the
fact that the amount of the pyramidal tracts of white matter differs somewhat on
the two sides of the cord (see p. 24). More rarely considerable malformations
have been found to occur.

The white matter of the cord, especially that of the lateral and posterior columns,
increases gradually in amount from below upwards, receiving a considerable accession
opposite the roots of the larger nerves which supply the limbs. These relations are
strikingly shown in the appended curves (fig. 10) which have been constructed by
Ludwig and "Woroschiloff from measurements by Stilling. The amount of the grey
matter in the different regions is also given, as well as the sectional areas of the
roots of the spinal nerves. It is seen that opposite to the origins of the large nerves
there is a marked increase in the amount of grey matter.

The anterior or white commissure is likewise proportional in size to the entering
nerve-roots.

Characteristic features of the different regions of the cord. — In the
sacro-coccygeal region the bulk of the spinal cord is formed of grey matter which
has a comparatively thin mantle of white substance surrounding it. The posterior
cornua are nearly as thick as the anterior, and the isthmus of grey matter is relatively
thick. The lateral cornu (in the sacral region) is well marked. Both here and in
the lumbar region the number of nerve-cells imbedded in the grey matter is rela-
tively very large, a fact which is probably connected with the circumstance that
these regions are concerned with numerous and important reflex acts.

In the lumbar region the white matter begins to predominate, owning chiefly to
the accession of the large nerve-roots of the sacral and lumbar plexus, many of the
fibres to and from which are now running down and up the white columns of the
cord. The posterior horn and the grey matter in general is still thick, although in
the upper part of the lumbar region it has become thin and has more of the
character which is met with in the thoracic region. The lateral horn is not distinct.
The outline of the cord is beginning to be more circular, a shape which is maintained
as far as the second thoracic segment.

In the dorsal or thoracic region the chief characteristic is the relatively small
amount of grey matter, which forms two long slender crescents united by a narrow
isthmus, which both here and in the cervical region is placed nearer the ventral than
the dorsal aspect of the cord, whereas in the lumbar and sacral regions it lies near
the middle of the dorso-ventral axis. The white matter is absolutely as well as
relatively greater in amount than in the lumbar region. The lateral horn forms a
distinct acute prominence throughout the whole of the thoracic region, but is most
marked in the upper part. Clarke's column (see p. 10) is also to be seen near the
base of the posterior horn : it is most prominent at the lower part of the thoracic
region. In the upper part the postero-mesial column begins to be marked off from
the postero-lateral.

The cervical region is characterized by the fact that the cord, except at the upper-
most part, is of large size and tends to be somewhat flattened dorso-ventrally. The
increase in size affects both grey and white matter. The postero-mesial column is
now sharply marked off from the postero-lateral. Fibres of the spinal accessory
roots may be seen passing out from the lateral cornu. A reticular formation is seen
at the outer edge of the grey matter. Both the lateral and anterior cornua are large
and are fused together to form a mass of grey matter, triangular in section, and
tapering off dorsally into the base of the posterior horn. This horn and the substance
of Rolando are but slenderly developed, contrasting with the large development of
the same parts in the lumbar enlargement. The isthmus is thin, and the central
canal flattened dorso-ventrally.

INTERNAL STRUGTUHE.

11

In the uppermost segments (upper part of the cervical enlargement) the grey
matter is again diminished in amount and the cord has become circular in outline,
as in the dorsal region. The section has however the other cervical characteristics,
and there is a much more strongly marked anterior commissure than in the thoracic
cord. Opposite the first cervical nerve-roots the cord begins to merge into the
medulla oblongata or spinal bulb, and the passage of the pyramidal fibres from the
pyramids on one side of the bulb to the lateral tracb on the other side of the cord

Fig. 11. — TRANSVERSE SECTIONS OF SPINAL CORD AT DIFFERENT HEIGHTS. (W. R. Gowers.) TWICE THE

NATURAL SIZE.

The letters and numbers indicate the position of each section : Go. at level of coccygeal nerve ;
Sac. 4 of 4tb sacral ; L3 of 3rd lumbar, and so on. The grey substance is shaded dark, and the nerve-
cells within it are indicated by dots.

tends partially to obliterate the anterior median fissure and to cut up the grey
crescent.

In the cervical region the nerve-roots leave the cord nearly at a right angle and
close together ; in the other regions at an angle which is more or less oblique, the roots
being directed from the intervertebral foramina upwards towards the cord ; in the
thoracic region they succeed one another at relatively longer intervals than
elsewhere.

THE SPINAL CORD.

MICROSCOPIC STRUCTURE OF THE SPINAL CORD.

The white substance of the spinal cord is almost wholly composed of longitudinally
coursing medullated nerve-fibres, which in carmine-stained transverse sections of
the cord (fig. 12) appear as clear rings with a stained dot — the section of the axis-
cylinder — either in the middle of the ring or shifted somewhat to one side. The
fibres vary much in size, and in many parts of the section larger and smaller fibres
are intermixed, but some parts are characterised by containing many large fibres,
others for the most part small fibres. The largest fibres are in the circumferential
part of the anterior and lateral columns (and especially in the direct cerebellar tract),
the smallest in the part of the lateral column in the neighbourhood of the processus
reticularis, in the marginal bundle of Lissauer near the apex of the posterior horn, and
in the postero-mesial column. Very small fibres also occur scattered over the white

Fig. 12. — A SMALL PORTION OF A TRANSVEKS3 SECTION OP THE WHITE MATTER OF THE EUMAN SPINAL CORD.

HIGHLY MAGNIFIED. (E. A. S.)

a, a, superficial neuroglia ; b, b, transverse section of part of the lateral column of the cord (direct
cerebellar tract). The dark points are the axis-cylinders, and the clear areas the medullary substance
of the nerve-fibres : the superficial neuroglia exhibits the appearance of a fine network in which only the
nuclei of the neuroglia-cells are seen. One or two corpora amylacea (c.a) are embedded in the neuroglia,
which extends inwards among the nerve-fibres.

substance, especially in the anterior column. The white columns are imperfectly
divided into secondary columns by incomplete septa of fibrillar connective tissue
which are prolonged inwards from the inner layer of the pia mater, and convey
blood-vessels to the interior of the cord.

Immediately beneath the pia mater and closely investing the cord externally is a
layer of what in the fresh condition appears a homogeneous substance with nuclei
embedded in it here and there. In sections of the cord hardened in alcohol or
chromic salts, the substance in question is finely reticulated (fig. 12, a, a). The layer
which it forms is very thin over some parts of the surface but comparatively thick
in others, and where the pia septa pass into the cord, it accompanies and invests
them and their ramifications in the white substance, passing with them between the
irregular bundles of nerve-fibres. Not only does this subpial reticular substance
accompany the prolongations of the fibrillar tissue and largely assist in forming the
incomplete septa above mentioned, but it extends independently amongst the indi-
vidual nerve-fibres, occupying the interstices between them, and serving as a uniting
medium in which they are embedded. Hence it was named by Virchow the
neuroglia (nerve-cement). The nuclei in it belong for the most part to branched
fibrillated cells (neuroglia-cells) which occur in considerable numbers and may be

MICROSCOPIC STRUCTURE. 13

said to form the tissue ; some which are more conspicuous are known as the cells of
Deiters ; they appear stellate in section and are found in the larger interstices
between the nerve-fibres. Along the line of origin of the posterior roots the super-
ficial neuroglia dips inwards towards the horn of grey matter, and expands within it to
join the gelatinous substance of Rolando. This, as before mentioned, presents a
transparent jelly-like appearance in the fresh condition, but in sections of the
hardened cord it is finely reticular, containing numerous neuroglia-cells. Some of
the bundles of nerve-fibres of the posterior root traverse this substance, and it
contains many nerve-cells ; these are mostly of small size, but here and there one of
larger dimensions is met with.

In the constitution of the rest of the cornua the neuroglia takes part to a far
less extent than in the substantia gelatinosa. It is true that it is prolonged both
from this and from the white substance into the grey matter, and pervades the

Fig. 13. — SECTION OP THE THO-
RACIC SPINAL CORD OF A CHICK
EMBRYO OP 9 DAYS INCCBATION,
STAINED BY GoLGl's METHOD.

(Eamdn y Cajal. )

c, central canal ; v, ventral or
anterior ; d, dorsal or posterior
surface. The spongioblasts alone
are coloured and are seen to
extend from the central canal to
the periphery of the cord. Some
appear to be detached and in pro- .
cess of conversion into neuroglia-
cells.

latter throughout in every
part. But it is in great
measure obscured by the
proper nervous elements,
which in the grey substance
comprise both cells and
fibres. In the first place are found multipolar nerve-cells, many of large size,
scattered singly or occurring in groups throughout the grey substance. In connec-
tion with these and especially accumulated around the cells and cell-groups, is an
interlacement of the finest nerve-fibrils, which is derived partly from the ramified
processes of the nerve-cells, and partly from the ramification of nerve-fibres or of
collateral fibres which enter the grey matter from the nerve-fibres of the white
columns. Occupying a considerable portion of the grey matter, are nerve-fibres,
mostly of the medullated kind ; these and the axis-cylinder processes of the nerve-
cells traverse the grey matter in different directions, coursing for the most part in
bundles which intercross with one another, and confer on the grey matter a spongy
appearance. Hence it is sometimes known as the substantia. spongiosa.

Some of these bundles, which are fairly constant in position in many sections of the spinal
cord, have recently been described by Pal (see Bibliography).

The structure of the neuroglia is described in the part of this work which deals
with General Anatomy (Vol. I., p. 322). It is developed from the spongioblasts of
His (see Embryology, Vol. I., p. 57), which at an early period of development
extend from the central canal in the middle of the grey matter to the periphery of
the cord (fig. 13). (The same holds good for other regions of the cerebro-spinal axis).
At a subsequent period their continuity from the central canal to the surface can no
longer be recognized, although it is certain that even in the adult the cells which line

14 THE SPINAL CORD.

the central canal and ventricles of the brain extend a long and indefinite distance into
the grey matter. It is probable however that it is by transverse division of the
spongioblasts, preceded by division of their nuclei, that the neuroglia-cells are origin-
ally formed. At the same time it appears clear that although nerve-cells and
neuroglia-cells are functionally very different, their origin is not so dissimilar as was
at one time believed to be the case. It was taught formerly that the neuroglia is a
form of connective tissue (which it resembles functionally), and it was supposed that
its cells were developed from meso blast, but of late years there has been much doubt
cast upon its supposed mesoblastic origin, and the question is not yet fully decided.
The researches of His have tended however to show that both the spongioblasts
from which the neuroglia-cells are believed to originate and the neuroblasts which
give origin to the nerve-cells are both formed from the (at first undifferentiated)
cells of the neural epiblast (see Embryology, development of central nervous system).
The investigations of Ramon y Cajal upon the development of these elements in the
embryo chick and mammal further indicate that the distinction into spongioblasts
and neuroblasts is not a fundamental one, for cells which from their shape and
position would be classed amongst the spongioblasts of His may alter their character
and by throwing out an axis-cylinder process become transformed into nerve-cells.

Small concentrically striated globules, termed corpora amylacca, are frequently met with
in the neuroglia of the cord in man, as well as in many of the parts of the central nervous axis.
They appear to be composed of proteid substance but, although long recognized, their mode
of formation and their meaning are unknown.

DISTRIBUTION OF NERVE-CELLS IN THE SPINAL CORD.

In transverse sections of the cord it is seen that the nerve-cells are not equally
distributed throughout the grey substance, but are arranged in definite groups,
which occupy nearly the same relative position in successive sections. The groups
are therefore the sections of longitudinal tracts of grey matter rich in nerve-
cells, and these tracts are named the gangUonic or cell-columns of the grey matter.
The longitudinal continuity of the groups can be seen in sections of the cord
made parallel with its long axis and passing through the part of the grey matter
where the groups occur. In such longitudinal sections it may also be observed that
the cells tend, speaking generally, to be more extended parallel to the longitudinal
axis of the cord the longer the segments of the cord, as indicated by the entering
nerve-roots (Toldt). It may further be stated as a probable law, applicable at least
to the cells belonging to the same group or column, that the longer the nerve-fibre
which issues from a cell, the larger is the cell. Those segments of the cord
from which the longest nerve-fibres issue by the anterior root have the largest
anterior horn cells (Pierret).

Cell-column of anterior horn. — Of these groups or columnar tracts of nerve-
cells, the one which is most constant and contains the largest cells is found along
the whole of the ventral part of the anterior horn where the nerve-cells lie among
the issuing fibres of the anterior roots. There seems to be no doubt that many of
these anterior or motor nerve-fibres are directly continuous with the axis-cylinder
processes of nerve-cells of this group. Hence it is sometimes named the motor
cell-column, but it is more generally known as the cell-column of the anterior horn.
Its cells are in most parts collected into two groups, a lateral or ventro-lateral
(fig. 14, 1) nearer the lateral column of white matter, and a mesial (a) nearer the
anterior column ; in the cervical and lumbar enlargements there is a third, more
deeply seated, dorsal or dor so-lateral group (&').

Of these several groups of cells into which1 the anterior horn cell-column is
divisible, the one which is most constant along the whole length of the cord is the

MICROSCOPIC STRUCTURE.

15

CERVICAL.

ANTERIOR
ROOT-BUNDLES

Fig. 14. — SKCTIONS OF SPINAL CORD IN LOWER CERVICAL, MID-DORSAL, AND MID-LUMBAR REGIONS. (E. A. S.)
On the right side of each section the conducting tracts are indicated.

16 THE SPINAL CORD.

mesial group : on this account it is thought to give origin to the nerves which
supply the dorsal muscles of the spinal column. It is sometimes described as
forming two sub-groups, viz. : a dorso-mesial and a ventro-mesial.

The ventro-lateral group probably gives origin to the nerves which supply the
lateral and ventral muscles of the trunk, including the muscles of respiration. In
the cervical region it is described as consisting of two parts, one more laterally
situated, which gives origin to fibres of the spinal accessory, and another, more
mesially placed, which is believed to give off the fibres of the phrenic nerve. In
the lumbar enlargement it also tends to be sub-divided.

The dorso-lateral group is mainly developed in the cervical enlargement and
lumbar enlargement, and has an evident relationship to the nerve-roots of the
brachial and sacral plexuses. It also shows subordinate groupings, which probably
have special connections with particular groups of the limb-muscles. For various
conjectures regarding both these and other cell-groupings in the grey matter, the
reader may consult the paper by Kaiser, which is given in the Bibliography.

Some of the cells which are nearer the anterior commissure send their axis-
cylinder processes through this commissure to the anterior white column of the
other half of the cord : it is believed that these processes may be connected with
nerve-fibres of the corresponding anterior root of the other side.

In some of the lower vertebrates it may be made out that there are ^variations in the size
of the column of cells of the anterior horn in successive portions of the cord, the cells being-
more numerous opposite the points of entrance of the nerve-roots, the attachment of which
to the cord is in them more localized than in man and higher vertebrates. In this way some-
what of a segmental formation of the column is indicated, and in some fishes and reptiles
the enlargement of the group of cells and its enclosing grey matter is sufficiently marked to
produce an external swelling opposite each nerve-pair. A similar segmentation is indicated in
an early stage of development in all vertebrates, including man, by the fact that the cord is
somewhat enlarged opposite each pair of nerve-roots.

Clarke's column.— A second very well marked group or column of large cells,
which occupies in transverse section an area at the inner or mesial angle of the base
of the posterior horn (fig. 14,/), and appears cut off from the rest of the grey matter
by a curved bundle of fibres derived from the posterior root, extends along the
middle region of the cord from about the third lumbar to the seventh cervical
nerve. This was termed by Lockhart Clarke the posterior vesicular column;
it is usually known as Clarke's column, although the cells were first noticed by
Stilling. It is best developed in the lower part of the dorsal (thoracic) region.
Prom the fact that it is almost entirely confined to the thoracic region of the cord
it was termed by Stilling the " dorsal nucleus." But although ceasing above and
below the points mentioned, it is not altogether unrepresented in other parts, for
groups of cells are found in a similar situation opposite the origin of the second and
third sacral nerves (" sacral nucleus " of Stilling) and opposite the origin of the third
and fourth cervical nerves (" cervical nucleus ") ; and elsewhere there are scattered
cells of the same character in the same part of the section of the cord. The cells of
this column, like most, if not all, the cells of the spinal cord, are multipolar, and
their axis-cylinder processes tend towards the lateral column, where they are believed
to form the direct cerebellar tract (Flechsig). The cells themselves are surrounded
by a fine plexus of nerve-fibrils, probably derived from collaterals of the posterior
root-fibres. They are of large size, measuring, according to Mott, in their longest
diameter, which is directed longitudinally, from 40yu to 90/i, the largest being found
in the lowermost part of the column. In the foetus and even in the new-born child
they are much smaller (25/x to 30/j), but by the second or third year after birth
they have nearly attained the same size as in the adult.

Lateral cell-column. — A third column of cells lies in the intermedio-lateral

MICROSCOPIC STRUCTURE. :17

tract (lateral cell-column, fig. 14, d). Like that tract, the ganglionic column it
contains chiefly appears as a distinct formation in the thoracic region ; in other parts
the cells do not form so distinct a group, but they appear nevertheless to be repre-
sented to some extent along the whole cord. Its cells are bipolar or multipolar, and
measure on an average 80/z in diameter, being considerably smaller than those of
Clarke's column or those of the anterior horn. In the upper part of the cervical
region a group of cells becomes distinct in a similar situation (lateral nucleus), and
is traversed by the roots of the spinal accessory nerve.

Middle cell-column (Waldeyer). — This is formed of what in sections of the
cord forms an ill-defined group of moderately-sized cells placed in the middle of the
grey matter of the crescent. The cells are most distinct as a group in the cervical
region, and also more numerous there, becoming fewer in number as Clarke's column
becomes more evident. In the dorsal region they lie mostly at the side of Clarke's
column, but further down they again move nearer the middle of the crescent. They
are distinguishable right down into the sacral region. It is not known with what
fibres they are connected, but fibres from the postero-lateral columns course amongst
them, and it may be that, on the other hand, they give off nerve-processes to one of
the conducting tracts ( ? to the antero-lateral ascending tract). They stain less
deeply with carmine than those of the motor column or of Clarke's column.

Cells of posterior horn ; solitary cells. — The cells of the posterior horn
are not grouped very definitely, but for purposes of description they may be roughly
sub-divided into — 1, those at the base of the horn ; 2, those near the middle of the
horn ; 3, those at the margins ; and 4, those of the gelatinous substance of Rolando.
They vary in size, some of the largest being found near the mesial margin of the
horn ; these often have a characteristic long curved process (comet-cell, Waldeyer) :
and even within the same group both large and small cells may be found intermixed.

But in addition to the groups, a number of scattered cells are met with, dis-
tributed through the posterior horn. These cells vary much in form and size, but
are for the most part spindle-shaped. They are usually spoken of as the solitary
cells. The axis-cylinder processes both from some of these cells and from cells of the
lateral cell-column pass towards the anterior horn and also towards the anterior
commissure, and they are believed to give origin to the smaller fibres which issue
with the anterior roots. Some of the axis-cylinder processes of these cells do not
however leave the grey matter but are branched and their ramifications lose them-
selves in the interlacement of fibrils which invests other cells. In the lamprey it has
been shown by Freud that cells which appear to correspond with the solitary cells
send their axis-cylinders into the posterior roots, and more than one observer has
described a direct passage of the axis-cylinder process of one of the more deeply
lying cells of the anterior horn through the grey matter into the posterior root, and
thence past the ganglion into the mixed nerve without coming into connexion
with any of the ganglion-cells.

The cells of the substance of Rolando were first noticed by Gierke. They are
small round granule-like cells, closely packed and staining with difficulty. They
appear to have been often taken for neuroglia cells, but, according to Gierke and
H. Virchow, there is little doubt about their nervous nature.

Cells are occasionally found separated from the general mass of grey matter and
lying out amongst the fibres of the white columns. These " outlying cells " have
been described by Stilling and others, recently in detail by Sherrington.

It has been shown by Golgi that the nerve-cells of the central nervous system may be
primarily classified under two heads, viz., 1, those with a long axis-cylinder process which
becomes a medullated nerve-fibre ; and 2, those with a short axis-cylinder process which may
or may not become medullated, and soon ramifies and loses itself in neighbouring parts of
the grey matter. Golgi is of opinion that the former are to be looked upon as " motor or

VOL. III. C

18

THE SPINAL CORD.

efferent " cells, and the latter as " sensory or afferent." but it is doubtful if this physiological
distinction will hold good. In the spinal cord the cells of the anterior horn, those of
Clarke's column, and many of the cells of the lateral cell-column and of the posterior horn
belong1' to the first category, while many of the solitary cells, the small cells of the substance
of Rolando, and some of those of the lateral cell-column, belong to the latter.

lug. 1.3. — CENTRAL CANAL SHOWING ITS KPITHKLIUM (E. A. S. )

A, from a child of six. Magnified 150 diameters. A', some of the ciliated cells, highly magnified.

B, section of the isthmus from the lumbar cord of an adult (set. 33), showing the central canal in the
middle surrounded by the substantia gelatinosa centralis. f.a., anterior median fissure ; p.m.c. ,
posterior white column ; a. c. , anterior white commissure. Magnified 30 diameters.

Commissures. — The anterior commissure (fig. 15, B, a.c.) consists of medul-
lated nerve-fibres which pass on each side, some into the anterior white column,
others into the anterior horn of grey matter. Their course is not strictly transverse,
many fibres which enter the ventral part of the commissure at one side leave it at
the dorsal portion on the other side. There is thus an oblique decussation at the
middle line (fig. 15). This decussation is most distinctly seen in the comparatively
short and wide commissure of the lumbar region, and in the upper part of the cervical
region. In the latter situation it appears as a continuation of the decussation of the
pyramids of the medulla oblongata, to be afterwards described. In addition to the
transverse there are a few longitudinal bundles of fibres in the region of this commis-
sure. The fibres are often somewhat displaced by vessels which pass into the grey
substance from the anterior fissure.

The posterior commissure also contains medullated fibres running trans-
versely or with a slight obliquity, but there is a large amount of neuroglia between
them, and this gives the commissure a grey aspect. In this commissure is
contained the central canal of the spinal cord surrounded by an area free from
medullated nerve-fibres, and occupied by a substance which, like the superficial
neuroglia and the substance of Rolando, has in the hardened condition a reticulated
structure and in the fresh state a gelatinous aspect. It is termed substantia gelatinosa

ORIGIN OF THE SPINAL NERVES.

19

centratis. In this gelatinous substance many of the fibres of the posterior com-
missure appear to end (see fig. 15, B). There is rather more of the posterior com-
missure behind the central canal than in front. The fibres of the posterior part curve
backwards on reaching the crescents of grey matter and pass towards the bundles of
the posterior roots, whereas the rest diverge at various angles into the crescent.

The central canal is lined with a layer of ciliated epithelium (iig. 15, A, A').
Each cell is provided with a bunch of cilia on the side which is turned towards the

SPINAL GANGUON
CEL!

POSTERIOR ROOT

I . W

FJBRES/OF .T/XANTEROLPrreRAI-

ANT, ROQT

Fig. 16. — DIAGRAM TO ILLUSTRATE THE RELATIONS OF THE ENTERING NKRVE-ROOTS, AND THK FIBRES

OF THE WHITE COLUMNS OF THE SPINAL CORD TO THE NERVE-CELLS IN THB GREY MATTER. (E.A.S.)

lumen of the canal : the other end of the cell is prolonged into the reticular
substance just mentioned, and there becomes lost to view.

In the adult human subject the lumen of the central canal is not unfrequently
obliterated, being filled up by detached cells.

OKIGIN OF THE SPINAL NERVES.

The roots of the spinal nerves are attached along the sides of the cord, opposite
to the corresponding horns of the grey matter ; the posterior roots entering along a
straight line at the postero-lateral groove, and the anterior roots being scattered
somewhat irregularly upon the surface (fig. 7, B).

The anterior roots are seen in a transverse section to pass through the white
substance and to enter the grey cornu in several bundles, which have a slight upward
inclination, so as to be often cut obliquely if the section be exactly in a transverse
plane. Some of the fibres on reaching the grey matter are directly connected with
the axis-cylinder processes of the large nerve-cells of the cornu. Others pass by
the cells without, so far as can be seen, entering immediately into relation with
them.

As soon as the bundles enter the grey matter, their fibres diverge from one
another, some passing mesially, others laterally, and others straight backwards (fig. 16).
Of those which pass mesially some are continued into the axis-cylinder processes of

c 2

20

THE SPINAL CORD.

the mesial group of cells of the anterior cornu, and others to the other side of the
cord through the anterior commissure, there perhaps to become connected with the
corresponding cells. The outwardly directed fibres of the root are connected with
the cells which form the lateral groups of the anterior horn, and partly with some
of the cells of the intermediate cell-column. The middle fibres are partly con-
nected to the cells of the anterior horn, and partly pass on to the posterior
horn, where they are probably continued into some of the cells there present.

In the cervical region of the cord, from the sixth nerve upwards, the root-fibres of the
spinal part of the spinal accessory nerve may also be seen passing out of the anterior horn
through the lateral column (fig. 31, p. 40). They arise from a group of somewhat large cells,
which in the uppermost region of the cord lies in the antero-lateral part of the horn, close to

Pig. 17. — TRANSVERSE SECTION OF THE SPINAL CORD OF A CHICK ON THE 9in DAY OF INCUBATION,
PREPARED BY GOLGI'S METHOD (Ramon y Cajal).

A , axis-cylinders of anterior root-fibres issuing from large cells of the anterior horn, C.

B, Posterior root-fibres passing from the bipolar cells of the spinal ganglion, into the posterior column
of the spinal cord, D, where they bifurcate, d, and become longitudinal ; e, f, y, collaterals from these
fibres, passing into the grey matter.

its ventral edge, but in the middle and lower cervical regions tends gradually to occupy a
position nearer the base of the horn (see p. 16). This group of cells is the direct continuation
downwards of the accessory nucleus which will be seen in the lower part of the medulla
oblongata.

The posterior roots at their entrance into the cord are seen to separate into
two sets. Of these the lateral, which contains most of the smallest fibres of the
root, enters opposite the tip of the posterior horn and joins a bundle of fine longitu-
dinal fibres which lies close to the periphery of the cord in this situation. This bundle
is known as the marginal bundle or column of Lissamr. Its fibres, which are
evidently different from most of those which enter with the posterior root, for they
acquire their medullary sheath considerably later (Bechterew), appear, as they pass
vertically, gradually to lose themselves in the adjacent gelatinous substance. The mesial
set containing the larger and some smaller fibres of the posterior root passes into the

COLLATERAL FIBRES OF THE POSTERIOR ROOTS.

21

postero-lateral white column, with the longitudi-
nal fibres of which its fibres become continuous ;
from this column many of them sweep with
bold curves into the adjacent grey matter. At
their entrance into the cord their direction like
that of the bundles of fibres of the anterior roots
is in most regions of the cord obliquely upwards.

Fig. 18. — LONGITUDINAL SECTION OF THE POSTERIOR COLUMN

OP THE SPINAL CORD OF A CHICK ON THE 8lH DAY OF

INCUBATION (Ram6n y Cajal).

This figure shows the course of 5 entering fibres of the
posterior root . and some of the longitudinal fibres of the
posterior column.

A, A, fibres of the posterior root ; B, bifurcation of
one of them in form of a Y ; C, D, origin of collateral
branches ; E, fibres of Groll's tract, also giving off colla-
terals.

Collateral fibres of the posterior roots
and of the white columns. — It has been
definitely shown by Ramon y Cajal, whose
researches into this subject have been confirmed
by Kolliker and v. Gehuchten, that the fibres of
the posterior roots as they enter the cord join by
a Y" or T~snaPe(l junction with longitudinal
fibres of the posterior column ; in other words
that they bifurcate as they enter the cord into
two principal branches which run upwards and
downwards in the posterior white column or in
the adjacent part of the posterior cornu. It
has also been proved by the same observers

Fig. 1 9. — TRANSVERSE SECTION OF THE CORD OF A CHICK ON THE QTH DAY (Ramon y Cajal).

This figure shows collaterals passing into the grey matter from all the white columns of the cord.
They are seen to form an especially close plexus in the posterior horn, just within the substance of
Bolando, and in the posterior commissure.

c, central canal ; v, anterior and d, posterior surface of the cord ; p, p, posterior roots.

22 THE SPINAL CORD.

that both from the root-fibre before its bifurcation and from its ascending and
descending stems there are given off at tolerably freqnent intervals "collateral"
branches which are directed inwards towards the grey matter ; into which they
penetrate for a variable distance and within which they ultimately end by breaking
up into a ramification of nerve-fibrils which may frequently be seen to have a close
relationship to cells of the grey matter. In this way collateral fibres are given off
from the posterior root-fibres and from their longitudinal extensions, some of which
penetrate as far as the anterior horn of the same side, others pass through the
posterior commissure into the grey matter of the opposite side, others towards the
lateral horn and intermediate cell-column, whilst others do not extend beyond the
posterior horn, passing towards Clarke's column or the solitary cells of the crescent,
while many end in or near the substance of Rolando. These collateral fibres can
be seen in sections of the embryonic cord which have been prepared by Golgi's
method, to pass into the grey matter in large numbers from the posterior columns,
most of the fibres of which are in fact prolongations of posterior roots which
have entered the cord. But they are by no means confined to the fibres of the
posterior columns, for from all the longitudinal white columns of the cord the
same convergence of collateral fibres into the grey matter can be seen (see figs. 16
to 20).

The passage of collateral fibres into the grey matter from the white columns of the cord
was first noticed by Golgi, who stated that the fibres of the anterior roots also give off in their
passage towards the surface of the cord fine lateral ramuscles which become lost in the adja-
cent nervous matter. Other observers have for the most part failed to detect these collaterals
of the anterior root-fibres.

COURSE OF NERVE-FIBRES WITHIN THE SPINAL CORD: CONDUCTING TRACTS.

It is impossible mechanically to unravel the tracts of nerve-fibres in their passage
along the spinal cord, and it is exceedingly difficult to trace the same fibre or fibres
for any distance in microscopical sections of the organ. But the task of following
out the course of certain sets of fibres has been much facilitated of late years by the
application to the subject of certain special developmental and pathological methods
of [ observation. Thus it is found that if the development of the spinal cord is
carefully observed, the medullary substance of the nerve-fibres is formed later along
certain tracts of the white columns than in the rest of the white matter, appearing
first in those tracts which are the immediate prolongations of peripheral nerves, and
being longest delayed in those which are connected with the higher centres in the
brain, so that in transverse sections of the cord these non-medullated tracts are easily
distinguishable by their more transparent grey appearance and by their different
behaviour with staining fluids (Flechsig).

The following list (from Kahler) gives the order of formation of the myelin-sheath in
the several tracts of the cord : — 1. Fibres in anterior column derived from anterior roots.
2. Postero-lateral column (its posterior part somewhat later than its anterior part). 3. The
lateral column near grey matter (the anterior part first, then the narrow posterior part between
pyramidal tract and posterior horn). 4. Postero-mesial column. 5. Direct cerebellar tract.
6. Antero-lateral ascending tract. 7. Pyramidal tracts (shortly before birth).

Another method by which similar results are arrived at consists in tracing the
course which the degeneration of the fibres pursues in consequence of a lesion either
in the 'encephalon, or in the spinal cord itself, or even in the peripheral nerves ; the
lesions being produced by accidental injury, by pathological changes, or experimen-
tally in animals. The degenerations which follow are either the result of the
Wallerian law that separation of a nerve-fibre from the nerve-cell with which it is
connected and from which it has grown out is followed by degenerative changes in

COURSE OF NERVE-FIBRES.

Fig. 20. — DIAGRAM SHOWING THK PRO-
BABLE RELATIONS OF SOME OF THK
PRINCIPAL CELLS AND FIBRES OF
THE CEREBRO-SPINAL SYSTEM TO ONE
ANOTHER. (E.A.S.)

1, a cell of the cortex cerebri ; 2, its
axis-cylinder or nerve-process passing
down in the pyramidal tract, and giving
off collaterals, some of which, 3, 3, end
in arborisations around cells of the ante-
rior horn of the spinal cord, the main
fibre having a similar ending at 4 ; call. ,
a collateral passing in the corpus callosum
to the cortex of the opposite side ; sir. , a
collateral passing into the corpus stria-
turn ; 5, axis-cylinder process of anterior cornu-cell passing to form a terminal arborisation in the end-
plate of a muscle-fibre, m.

6, a cell of one of the spinal ganglia. Its axis-cylinder process bifurcates, and one branch, 7, passes
to the periphery to end in an arborisation in the sensory surface, ». The other (central) branch bifurcates
after entering the cord (at 8), and its divisions pass upwards and downwards (the latter for a short
distance only) ; 9, ending of the descending branch in a terminal arborisation around a cell of the
posterior horn, the axis-cylinder process of which, again, ends in a similar arborisation around a cell of
the anterior horn ; 10, a collateral passing from the ascending division directly to envelop a cell of the
anterior horn ; 11, one passing to envelop a cell of Clarke's column ; 12, a collateral having connections
like those of 9 ; 13, ending of the ascending division of the posterior root-fibre around one of the cells of
the posterior columns of the bulb ; 14, 14, axis-cylinder processes of cells of the posterior horn passing
to form an arborisation around the motor cells ; 15, a fibre of the ascending cerebellar tract passing up
to form an arborisation around a cell of the cerebellum ; 16, axis-cylinder process of this cell passing
down the bulb and cord, and giving off collaterals to envelop the cells of the anterior horn ; 17, axis-
cylinder process of one of the cells of the posterior column of the bulb passing as a fibre of the fillet to
the cerebrum, and forming a terminal arborisation around one of the smaller cerebral cells ; 18, axis-
cylinder process of this cell, forming an arborisation around the pyramidal-cell, 1.

24 -.;. THE SPINAL CORD.

the part of the fibre thus separated from that centre (secondary degenerations], or they
may follow from the prolonged disuse of a nervous tract, especially in young animals,
as when a limb has been removed or from some other cause (tertiary degenerations).
The degeneration which follows a lesion of part of the nervous centre, and especially
section of the spinal cord, is in some tracts above the lesion, in which case the
degenerated tract is styled "ascending," in others below ("descending") (see also,
p. 27). The place of the degenerated nervous substance is ultimately taken by a
non-nervous fibrillar tissue, which, by its difference of behaviour to staining fluids,
can easily be distinguished from the surrounding undegenerated white substance
(stage of sclerosis). In new-born and young animals, after a longer interval, groups
of nerve-cells are affected by the degenerative processes, and the cells may even
eventually disappear altogether (v. Gudden). When this is the case it may be
assumed that they are in connection with the fibres which have been cut ; these
being probably the axis-cylinder processes of the cells.

Thus in a rabbit in which, immediately after birth the sciatic trunk is resected, when the
animal is full-grown the corresponding anterior cornual cells are found to have become
atrophied, and similar results are obtained with motor nerves generally, both spinal and
cranial (v. Gudden, Forel, Ganger, Mayser).

Tracts of the antero-lateral column. — Several tracts can by these methods
be traced in the antero-lateral column, not only along a great part of the spinal cord,
but into or from certain parts of the encephalon. The long tracts in this column
are the direct and crossed pyramidal (descending), the antero-lateral or ventro-lateral
ascending, the antero-lateral or ventro-lateral descending, and the dor so-lateral
ascending (or direct cerebellar).

Descending tracts in the antero-lateral column. — The pyramidal tract
is directly traceable down from the opposite pyramid of the medulla oblongata, and
ultimately from the cerebral cortex (Rolandic region). The greater number of the
fibres which compose the pyramid cross at the upper limit of the spinal cord, down
which they pass in the posterior part of the lateral column as a compact bundle of
fibres occupying in transverse section a somewhat triangular area, which lies in the
angle between the posterior horn and the outer surface of the cord, but is in most
parts separated from both by fibres belonging to other systems. This lai&ral or
crossed part of the pyramidal tract (figs. 14 and 24), can be traced as far as the third or
fourth pair of sacral nerves, becoming gradually smaller below and approaching the
surface of the cord.

A few fibres of the pyramidal tract are found scattered in other parts of the
antero-lateral column.

Some of the fibres of the pyramids of the medulla oblongata do not decussate at the
upper limit of the cord. These pass down close to the anterior median fissure, forming
the anterior or direct portion of the pyramidal tract (fig. 14) (column of Turck), which
gradually diminishes as it is traced downwards, and usually ceases altogether at
about the middle of the dorsal region of the cord. It is probable that the decus-
sation of these anterior pyramidal tracts goes on along their whole course, their
fibres passing through the anterior commissure and through the grey matter of the
opposite side to reach the lateral pyramidal tract on the other side of the cord.

There is much variation in the development of the anterior pyramidal tracts in different
individuals. In some they are so well marked as to form a visible prominence on the surface
of the cord close to the anterior median fissure and separated from the rest of the anterior
column by a groove, the anterior Intermediate sulctis of Rauber. In others they are quite small,
or may even fail altogether. In this case it may be assumed that the decussation of the pyra-
mids, which is known to be subject to considerable variation, has been more complete than
usual. In other cases again the anterior pyramidal tracts may be unsymmetrical, being

COURSE OF NERVE-FIBRES. • 25

more developed on one side than on the other, or the tract on one side may be wholly unde-
veloped. The direct tract is said to be wanting in 15 per cent, of cases in man. In different
animals there is also much variation in the position and size of the pyramidal tracts. A
well-marked direct pyramidal tract appears to be absent in most animals, even in monkeys.
In some (mouse, rat, guinea-pig) the pyramidal tracts are in the posterior columns, but in
most animals (rabbit, cat, dog) they run in the lateral columns as in man. The fibres of the
pyramidal tract are probably connected with the anterior horn by collateral fibres, which ramify
amongst the large cells that give origin to the anterior nerve-roots (figs. 1 6, 20).

The pyramidal tracts are undoubtedly the paths by which voluntary impulses pass from
the brain to the various spinal segments. All the fibres within the area embraced by the
" tract " are not, however, of the same nature, although fibres of the one function predominate :
and this is probably correct of all the so-called " tracts " of conduction.

There are at least two descending tracts in the antero-lateral column, besides the
direct and crossed pyramidal. One, the antero-lateral descending cerebellar
tract (anterior marginal bundle of Loewenthal), consists of fibres which are connected
with cells in the cerebellar cortex of the same side, and which undergo degeneration
on removal of the corresponding half of the cerebellum (Marchi). These fibres form
an extensive circumferential tract in the anterior three-fourths of the antero-lateral
column, spreading inwards in front of the crossed pyramidal tract to reach the
intermedio-lateral tract of the grey matter. The tract which is thus marked out
(see fig. 26, p. 32) embraces (in the dog) the part of the anterior column which
in man is occupied by the direct pyramidal tract, and also the whole region of the
tract of Gowers (see below), the fibres of these two tracts being intermingled. Some
of the fibres of the anterior roots also exhibit degeneration after removal of the
cerebellar hemisphere, and are therefore probably directly continued from fibres of
this tract.

In the monkey a few fibres in this column degenerate after lesions of the cerebral
hemisphere of the opposite side. They are intermingled with those of the descending
cerebellar tract and with those of the tract of Gowers, and are connected with cells
in the Rolandic region of the cerebral cortex, as shown by the fact that they
degenerate after lesions of that region. These fibres may perhaps be regarded as
belonging to the system of the direct pyramidal tract, which in the monkey docs
not exist as a well-marked tract as in man : it has not yet been ascertained whether
they occur in man as well as the direct pyramidal.

Ascending tracts in the antero-lateral column. — The dorso-lateral
ascending cerebellar tract (direct lateral cerebellar tract of Flechsig) (fig. 14) lies
between the lateral pyramidal tract and the outer surface of the cord, occupying a
somewhat narrow area of the transverse section, which in the upper regions of the
cord reaches to the tip of the posterior horn, but lower down becomes more limited,
and is separated from the horn by the intervention of the adjoining pyramidal tract.
It begins to appear at the lower dorsal region in man, and is then seen in all sections
of the cord and lower part of the bulb, passing eventually by the restiform body
into the cerebellum (middle lobe) (see fig. 27, p. 33).

It is found that there are a few fibres scattered through the neighbouring parts
of the lateral column which, from their development simultaneously with those of
the cerebellar tract, should be apparently reckoned with it. The axis-cylinder
processes of the cells of Clarke's column are said to give origin to the fibres of the
dorso-lateral cerebellar tract. The fibres of this tract acquire their medullary sheath
somewhat earlier than those of the pyramidal tract. They are also considerably
larger.

The ventro -lateral or antero-lateral ascending cerebellar tract (antero-
lateral ascending tract of Gowers) occupies a position in the sectional area of the
lateral column which is anterior or ventral to the dorso-lateral cerebellar tract, and
It has in section an arched shape curving from immediately in front of the crossed

26 •• THE SPINAL CORD.

pyramidal tract (where it is most strongly marked) round the superficial part of the
lateral column in front of the dorso-lateral cerebellar tract, and tailing off gradually
between the issuing anterior roots to reach the anterior column. It can be traced
upwards into the medulla oblongata and pons Varolii (fig. 27), and eventually enters
the cerebellum along with the superior peduncle, passing mainly to the vermis. It is
uncertain from what cells the axis-cylinders of its constituent fibres spring, but it
is probable that they arise from some of the cells of the posterior horn. Its fibres
are intermingled with those of the descending cerebellar tract.

The remainder of the antero-lateral column which is not comprised in the above
tracts encircles the anterior cornu ; it is termed the antero-lateral ground-bundle.
It varies in sectional area with the size of the nerve-roots and of the grey matter,
and many of its fibres not improbably are of a commissural nature, serving to
connect the grey matter of different segments of the cord. It receives fibres also
from the grey matter of the other side through the anterior commissure (fig. 15, B,
a.c.), and is in part composed of fibres of the anterior roots which course for a
certain distance obliquely within it before leaving the cord. Many intersegmental
fibres also occur scattered amongst the fibres of the long tracts.

Tract of Lissauer. — At the posterior part of the lateral column, close to the
entering fibres of the posterior roots and directly derived from them, there is
constantly to be seen a well-marked bundle of fine nerve-fibres, which was first
described by Lissauer, and since by Bechterew and others. It is not always confined
to the lateral column, but may extend into the postero-lateral column.

Tracts of the posterior white column. — This column is mainly composed
of two long ascending tracts, viz., the tract of Goll, which about corresponds with
the postero-mesial column, and the tract of Burdach, which embraces the remainder
of the posterior column. In the lower part of the cord these two tracts are not
marked off from one another in the adult, but from the middle of the dorsal region
upwards the postero-mesial column is separated from the postero-lateral by a septum
of pia mater. Of the two parts of the posterior column the tract of Burdach is
mainly composed of rather large fibres which are joined by, i.e., are continuous with,
the large fibres of the entering posterior roots. After a certain course, in which they
give off numerous collaterals to the grey matter, they appear to enter the grey matter
and to come into intimate relationship, although not into actual continuity, with its
cells, especially those of Clarke's column. The fibres of the tract of Goll, on the
other hand, are for the most part of smaller diameter. They also are derived from
posterior root-fibres, but instead of soon entering the grey matter of the cord many
of them run up the postero-mesial column into the medulla oblongata, where they
terminate amongst the cells of the nucleus gracilis.

The column of Goll in the embryo shows a distinction into two parts, one mesial, close to
the posterior median fissure, and a dorso-lateral part, lying near the dorsal surface of the cord
(Flechsig).

Descending fibres of the posterior column.— In the middle of the
sectional area of the postero-lateral column a few fibres are constantly found,
which undergo descending degeneration after lesions of the cord. These are often
described as constituting a special tract (" comma " tract), but they are a good deal
intermingled with fibres of the adjacent ascending tracts. Whether they originate
from cells higher up in -the cord or are derived from the descending branches
of the posterior root-fibres is uncertain. The latter, it may be remembered, extend
a certain distance down the cord from the Y-shaped division of those fibres, giving
off collaterals to the grey matter, and ultimately themselves turning into the grey
matter. The extent to which these descending branches of the posterior roots may
pass down the cord has not as yet been determined.

DEGENERATIONS IN THE SPINAL CORD. 27

DEGENERATIONS IN THE SPINAL CORD AS THE RESULT OF LESIONS.

It necessarily results from the "Walleriau law of degeneration of nerve-fibres
(Vol. I., p. 356) that every lesion of the nervous system in which fibres are cut or
crushed must be followed by degeneration of nerve-fibres either above or below the
lesion according to the position of the cells from which the fibres have originally
grown, and which serve throughout life to maintain the nutrition of the fibres with
which they are connected. Any such degeneration which occurs above the lesion is
usually termed " ascending," and below the lesion " descending."

These terms must not be taken to imply, as is erroneously done by some authors, either that
the degeneration starts from the lesion and extends upwards or downwards along the fibres,
or that the nervous impulses which the fibres conduct necessarily have an ascending or a
descending direction. For it is known (1) that the degeneration in the peripheral part of a
cut nerve-fibre occurs simultaneously along its whole course ; (2) that a nerve-fibre may
undergo " descending " degeneration, although it normally conveys ascending impulses, e.g.,
the peripheral afferent nerves.

Since the terms ascending and descending as applied to nerve-degeneration lead to much
confusion of ideas it would be better, if possible, to discard them and to adopt words which
merely imply that the degenerative process occurs above or below a lesion. But unfortunately
those terms have taken such deep root in the literature of the subject that this course
would be very difficult, and might lead to even worse confusion than their retention.

Similarly, if the nerve-cells from which the fibres are thus derived are removed
or destroyed, the fibres, with any branches which they may give off, will degenerate
along their whole course. Hence any tracts of fibres in the spinal cord which are
derived from cells in parts of the brain, degenerate on destruction of those parts.
.Further, those fibres which have grown into the spinal cord or brain from nerve-cells
situated external to those organs (e.g., the fibres of posterior roots of spinal nerves and
corresponding fibres of cranial nerves) will, if cut between the spinal cord or brain
and the ganglion-cells from which they are derived, undergo degeneration from the
point of section, not only as far as the surface of the central organ, but also along
their whole course within that organ, and the degenerative process will include all
their branches. Thus much having been said to explain the meaning of the results
which are obtained by the study of nerve-degenerations, we may proceed to consider
the degenerations which occur within the spinal cord : (1) from section of the pos-
terior roots of the nerves ; (2) from lesion or removal of parts of the brain ; (3) from
section or other lesion of the spinal cord itself.

1. Degenerations resulting from section of the posterior roots. — These
have been investigated in the dog by Singer and Kahler, in the monkey by Mott
and Tooth. It is convenient in describing the effect of sections of the posterior
nerve-roots to consider them in the sacro-lumbar and in the dorso-cervical regions
respectively, although the course of the degenerative process is essentially similar in
both.

(a.} Section of the posterior roots of the sacro-lumbar nerves. — This has been
most satisfactorily investigated by Singer in the dog and by Mott in the monkey.
Section of these nerves, e.g., of the whole cauda equina, is followed by " ascending "
degeneration in the posterior column of the same side along the whole length of the
spinal cord and as far as the nucleus gracilis of the medulla oblongata. But the
degeneration does not occupy the same position and extent in every part of the
cord. At the lowest part it involves the whole of the posterior column (fig. 21, a),
but as soon as a point is reached at which uncut nerve-fibres enter the cord, these
now occupy the part of the column nearest the horn of grey matter, while degenerated
fibres are seen in that part only which is nearest the posterior median fissure (i).

28

THE SPINAL CORD.

In this situation they pass up the cord, diminishing in number, at first rapidly and
afterwards more slowly, until at length a relatively small tract of degeneration is
found, occupying the postero-mesial angle of Goll's tract, in which it runs to the
nucleus gracilis (fig. 21, e).

(J.) Section of the posterior roots of the dorsal and cervical nerves. — After section
of one or more of these roots degeneration occurs immediately above the section in
the part of the postero-lateral column which is next to the posterior horn (figs. 22,
23, a). Somewhat higher up this becomes separated from the horn by other uncut (and
therefore undegenerated) nerve-root-fibres, and approaches the postero-mesial column.
Still higher it is found to have reached that column, where it is represented by a smaller

Fig. 21. — DIAGRAM SHOWING THE LEGENERATIONS IN THE POSTERIOR COLUMN WHICH RESULT FROM

SECTION OF THE POSTERIOR ROOTS OF THE SECOND SACRAL TO THE SIXTH LUMBAR NERVES OF THE

DOG. (Singer. )

a, section at the level of the sixth lumbar ; b, at the fourth lumbar ; c, from the middle of the
thoracic region.

Fig. 22. — DIAGRAM OF DEGENERATIONS FOLLOWING SECTION OF THE ELEVENTH AND TWELFTH THORACIC

POSTERIOR NERVE-ROOTS OF THE DOG. (Singer.)

a, section at the level of the twelfth thoracic ; b, at the third thoracic ; c. at the middle of the
cervical region.

Fig. 23. — DIAGRAM OF THE DEGENERATIONS FOLLOWING BILATERAL SECTION OF THE SECOND THORACIC TO

THE FIFTH CERVICAL POSTERIOR NERVE-ROOTS OF THE DOG. (Kahler. )

«, at the level of the first thoracic ; b, at the sixth cervical ; c, at the first cervical.
(Figs. 21, 22, and 23 are copied from Toldt's " Gewebelehre.")

tract of degeneration, which in section lies obliquely across the column. With
regard to this degeneration in the postero-mesial column it is to be noted that while
that which results from section of the lower (lumbo- sacral) roots occupies in the
higher parts of the cord the postero-median angle, as above described, the degene-
ration resulting from section of dorsal roots lies next to this, that resulting from
section of lower cervical roots passes up Goll's column in its lateral part next
to the column of Burdach, and finally that resulting from section of upper cervical
roots is confined to Burdach's column, and ends in the nucleus cuneatus of the
medulla oblongata. In other words, the lower the root the more mesial is the
resulting long degeneration in the higher parts of the cord and in the medulla
oblongata. The fibres, as they enter the cord with the posterior nerve-roots, form

DEGENERATIONS IN THE SPINAL CORD. 29

in fact a succession of lamellar tracts, which lie in each case at first next to the
posterior cornu, and become gradually shifted medianwards by those which enter
the cord with the higher nerve-roots.

It is further to be noted that in all cases the degeneration falls off
markedly in amount as we trace it up the cord, and that what remains is
eventually confined to a part of the posterior column which contains normally
fine or medium-sized fibres only. From this it may be inferred that the larger
fibres of the posterior roots — which in fact form the bulk of those roots — have
a relatively limited course after entering the cord. They probably end by their
collateral branches, and ultimately by their main ascending branches, turning into
the grey matter and breaking up into terminal ramifications in the fine interlacements
of nerve-fibrils which occur in the neighbourhood of the nerve-cells and cell-groups.
These terminal branches and the nerve-fibrils which result from their ramifications,
should also, of course, from the Wallerian law, degenerate after section of the roots, and
there is no doubt that they actually do so, although from their scattered course in
the grey matter it is difficult to prove the fact. It has, however, been shown by
Mott that after section of the lower posterior roots, the fine nervous interlacement
which surrounds the cells of Clarke's column disappears for some little distance
above the entrance of the cut nerve-roots, and it may therefore be fairly inferred
that some of the fibres of the posterior roots give origin directly and by collaterals
to this interlacement. Others, probably, are similarly related to other cells, both in
the posterior and anterior horns of the same side, and even on the other side of
the cord, for it will be remembered that ramifying collaterals can be traced from the
posterior root-fibres to all these parts (see figs. 16 and 20). Thus all the larger and
some of the smaller * fibres of the posterior roots gradually end as they are prolonged
up the cord, until finally only those remain which pass up the postero-mesial
• column towards the medulla oblongata. Even these become gradually diminished
in number, no doubt from the fact that some of them terminate in the grey matter
as they proceed.

It will further be remembered that the fibres of the posterior roots divide on
their entrance into the cord into two main longitudinal branches, ascending and
descending. Of these the ascending only has been traced by the above degenerations,
but the descending branch must also undergo degeneration. It is, however, not
easy to trace out its course. The only known "descending" degeneration in the
posterior columns is along the narrow curved tract in the postero-lateral column
which is known as the "comma," but would be better termed the posterior
descending trad. Mott has found that this degeneration results not only in sections
of the cord, but also after section of posterior nerve-roots, and that it has a
limited extent, one or two centimeters only. It is therefore not improbable that
this degeneration may represent the descending branches of the cut posterior root-
fibres (cf. p. 26, and fig. 20, 8 to 9).

It will be convenient here to sum up what is known or may be inferred as to the course
of the fibres of the posterior roots within the cord as determined by anatomical, embryological
and experimental (degenerative) methods. (1.) Each fibre on entering the cord divides into
an ascending and a descending branch, which form the longitudinal fibres of the posterior
column. Both from the root-fibre before division and from the branches, collaterals come off
which lose themselves in terminal ramifications enveloping nerve-cells in the grey matter.
Probably also after a longer or shorter course the main branches terminate by passing in like
manner into the grey matter. (2.) From each root on entering the cord a lateral bundle of
small fibres (Lissauer's bundle) is given off, which lies partly lateral and partly mesial to
the apex cornu posterioris, while the remainder of the root forms a large lamellar bundle of
mixed large and small fibres which run longitudinally in the postero-lateral column close
to the cornu of grey matter. (3.) From this lamellar bundle many fibres pass upward

1 Those of Lissauer's bundle.

30

THE SPINAL CORD.

along the whole length of the cord, being gradually shifted inward towards the postero-
mesial column, and forming as they reach this column the tract of (roll, which becomes the
funiculus gracilis in the medulla oblongata ; from the tract of Goll the fibres eventually
pass, some into the grey matter of the upper part of the spinal cord, others into grey matter
in the nucleus gracilis of the bulb, whilst yet others derived from the uppermost
cervical roots do not reach the tract of Goll but pass up to the bulb in the funiculus cuneatus
and end in its nucleus. (4.) The remainder of the fibres which have entered by the

corp. quoudr. cmt.

meci. obi.

Fig. 24. — DEGENERATIONS IN THE MESENCEPHALON, PONS VAROLII, MEDULLA OBLONGATA, AND SPINAL

CORD OF A MONKEY, FOLLOWING A LESION OF THE ASCENDING FRONTAL CONVOLUTION. (E.A.S.).

The lesion was on the right side of the brain. The section outlines are drawn to one scale. The
degenerated fibres are shown by black dots.

The degeneration is mainly on the same side in the mesencephalon, pons, and bulb, but on the
opposite side in the spinal cord. A few fibres are degenerated in the antero-lateral region in the oord,
but the degeneration is otherwise confined to the pyramidal tracts.

DEGENERATIONS IN THE SPINAL COED. 31

posterior roots have only a limited course up the postero-lateral column, passing-, as they
ascend, into the grey matter, in which they and their collaterals form the fine nervous
plexus around many of the nerve-cells which has been already mentioned. From some of
the large fibres the plexus around the cells of Clarke's column (and perhaps also around
the cells of the nucleus cuneatus of the medulla oblongata) is in this way formed, whilst
others furnish an enveloping1 plexus to the cells of the anterior horn and to those of other
parts of the grey matter. (5.) The descending- main branches of the posterior root-fibres
have, like many of the ascending branches, only a limited course, during which they give off
collaterals, by means of which, and also ultimately by directly passing into the grey matter,
they assist in forming the enveloping plexus around the nerve-cells of the segments of the
cord immediately below that at which the parent root has entered (compare figs. l(j and 20).

2. Degenerations in the spinal cord resulting from lesions of parts of
the brain. — Removal of the cortex of the so-called " motor " region of the cerebral
hemisphere is followed by degeneration extending along the pyramidal tract in the
brain and cord (fig. 24). In the spinal cord this tract has for the most part crossed
to the opposite side, but in man a portion runs for a time as the direct tract along

Fig. 25. — DIAGRAMS SHOWING THE DEGENEKATIOKS IN THE SPINAL CORD *

WHICH RESULT FROM REMOVAL OP PORTIONS OF THE CEREBRAL CORTEX

OF THE MONKEY (France).

A, upper thoracic cord from a monkey in which the left marginal
gyrus had been removed some months before death. Sclerosis in both
crossed pyramidal tracts, but most on the opposite side.

B, mid-thoracic cord from a monkey in which the right gyrus fornicatus
had been destroyed some months before death. Sclerosis in the opposite
pyramidal tract.

the anterior median fissure on the same side as the lesion (fig.
14). Although this direct pyramidal tract is usually considered
to be confined to the anterior column, it is found in the
monkey as the result of lesions of the motor regions of the V,( ,1 - ? /

cortex that there are a few scattered fibres in the circum-
ferential part of the antero-lateral column which also under-
go degeneration (descending cerebral fibres of the antero-
lateral column, see p. 25). The crossed tract lies in the posterior part of the
lateral column between the direct (dorso-lateral) cerebellar tract and the posterior
horn, and in this situation the degeneration can be traced downwards, decreasing
in amount, and, in the lower parts of the cord, with the disappearance of the
dorso-lateral cerebellar tract, approaching the surface of the cord near the tip of the
posterior horn. In the cervical region the crossed pyramidal degeneration may reach
the surface of the cord in front of, i.e., ventral to the dorso-lateral cerebellar tract,
which is partly enclosed by the degenerated fibres ; this, at least, is the case in the
monkey (fig. 25, A). After a unilateral lesion of the cortex there is also a certain
amount of degeneration in the lateral tract of the cordon the same side as the lesion.
This is especially the case when the lesion has involved the marginal convolution
(fig. 25, A). These are not, as might be supposed, fibres which have passed from
the pyramid of the medulla oblongata directly to the lateral column of the same
side of the cord, but they may be traced from the lesion of the cerebral cortex
across the corpus callosum into the internal capsule of the opposite side, whence
they run down the crusta and pyramid bundles of the pons and bulb to re-cross at
the decussation of the pyramids, and thus to reach the pyramidal tract of the
cord on the same side as the lesion. Although most numerous in the higher
parts of the nerve-centres, a few of these re-crossed fibres are found to extend right
along the spinal cord.

On the other hand, section of the pyramidal tract in the cord of the new-born animal is
followed by atrophy of the large cells of the " motor " area of the cortex (v. Monakow).

32 THE SPINAL CORD.

Destruction of the gyms fornicatus of one hemisphere is also followed by degeneration
extending down the pyramidal tract, although the gyrus fornicatus cannot be reckoned in
with the <; motor " region of the cortex cerebri, but rather appears to be connected with the
appreciation of sensory impressions. Since, however, it is not possible to cut away the gyrus
fornicatus without pushing aside and thus somewhat injuring the motor cortex, it may
be alleged that the degeneration in question is really the result of such injury to that cortex.
Nevertheless there is no serious improbability in supposing that afferent as well as efferent
fibres are conveyed along the course of the pyramidal tract. Indeed, so far as experimental
evidence upon animals is of value in determining the course of afferent impressions along the
cord, it is rather in favour of some kinds at least of those impressions passing up this part of
the lateral column.

Marchi and Algieri found extensive degeneration in the tracts of Burdach after removal of
a part of the cortex a little behind the motor zone in the dog, and also after removal of the
occipital lobe ; in the latter case combined with some degeneration in Goll's column. Singer
and Munzer were unable to confirm these results.

Sherrington finds, after removal of parts of the cortex cerebri, a few scattered degenerated
fibres in the anterior and lateral cornua of the spinal cord (and also in the grey matter of the
pons and in the substantia nigra of the crus cerebri). The same observer has noticed that
even when the cortical lesion is entirely confined to the so-called " arm-area " of the cortex, a
certain number of fibres are found to degenerate right down the pyramidal tract of the oppo-
site side, even as far as the lumbo-sacral region.

3. Degenerations in the spinal cord resulting from lesions of the cere-
bellum.— These have been described by Marchi, who has found, as above mentioned

Fig. 26. — SECTION OF SPINAL CORD OF DOG (LUMBAR RKGION) KILLED

THREE MONTHS AFTER REMOVAL OF THE RIGHT HALF OF THE

CEREBELLUM (Marchi). THE DEGENERATED PART is SHADED

WITH DOTS.

(p. 25), that removal of one lateral half of the cerebellum
in the dog is followed by degeneration extending down the
circumferential part of the antero-lateral column. The
degeneration is most extensive in the upper regions, and
gradually lessens in the lower parts of the cord, but can
be traced almost to its termination. It also extends

along some of the fibres of the anterior roots, thus indicating a direct connection
between these and the cerebellar cortex (fig. 26, «, d).

4. Degenerations resulting from lesions of the cord itself. — a. Sec-
tion of the spinal cord in any part is followed by certain degenerations above
and certain below the section. These may be classed as 1, Short degenera-
tions which extend only a limited distance above or below the plane of section ;
and 2, long degenerations which extend an unlimited distance upwards or downwards
in the cord. Of the short degenerations, the most marked are in the anterior
column and the anterior part of the lateral column near the grey matter (antero-
lateral ground-bundle), where there are seen numerous scattered degenerated fibres
both ascending and descending ; they probably are due to the section of fibres
which serve to connect cells of one segment of the cord to the grey matter of
other segments above or below. Of the long degenerations, the " descending "
ones are those of the pyramidal tracts, crossed and direct ; the descending
cerebellar tract of the antero-lateral column, and, for a few centimeters, the small
descending tract (comma tract) of the posterior column ; the "ascending" are in
the posterior column, where they are the same as would have resulted from section
of all the posterior roots below the point of section, and in the lateral column in
the situation of the direct (dorso-lateral ) cerebellar tract and of the antero-lateral
ascending tract. The continuation of these towards the brain has already been
mentioned (p. 25) and will again be referred to in connection with the medulla
oblongata and pons Varolii.

DEGENERATIONS IN THE SPINAL CORD.

If the section of the cord is confined to one lateral half the tracts of degeneration
are limited to the side of the hemisectiou, but a few degenerated fibres are seen in
the corresponding tracts upon the other side above the hemisection (fig. 27).

Medulla. oTrlonc/ata

d.a.c.

Fig. 27. — DEGENERATIONS IN THE SPINAL CORD, MEDULLA OBLONGATA, PONS VAROLII AND MESEN-

CEPHALON OP A MONKEY, FOLLOWING HEMISECTION AT THE 12TH DORSAL NERVE. (E.A.S.)

The hemisection was on the left side of the cord and complete. The section-outlines drawn to one
scale with a camera lucida. The degenerated fibres shown by black dots. Those in the section of the
lumbar cord are descending, all the rest are ascending, py. , pyramidal tract ; d.a.l., descending antero-
lateral tract ; d. a. c., dorso- lateral ascending cerebellar tract; d'.a'.c'. (in Pons III.), degeneration of
fibres of this tract in the white matter of the cerebellar worm ; v.a.c. , ventro-lateral ascending cere-
bellar tract (Gower's tract); v'.a'.c'. (in Pons II. and III.), degenerated fibres of this tract passing
dorsally into the valve of Vieussens (in Pons III. ) and into the white matter of the vermis (in Pons II. ) ;
n.III., n.V., n.VL, n.VJI., issuing fibres of the 3rd, 5th, 6th, and 7th nerve-roots; v.IV. , 4th
ventricle.

Nearly all the degeneration is on the same side as the lesion. A few fibres are degenerated on the
opposite side (perhaps from a slight accidental injury of that side of the cord).

VOL. III. D

34 RECENT LITERATURE.

According to L. Auerbach destruction in the cat of a considerable length of the posterior
part of one half the spinal cord, including the posterior white column, the posterior horn of
grey matter, and the posterior part of the lateral column, is followed by degenerations (ascend-
ing) in the dorsal cerebellar tract and antero-lateral remainder of the opposite side, with degene-
rated fibres in the anterior commissure (besides the well-known ascending degenerations of the
same side). The number of degenerated fibres diminishes gradually as they are traced upwards.
In the medulla oblongata they are few in number and mostly on the side opposite the lesion,
dorsal to the olivary nucleus ; a very few on the same side dorsal to the nucleus lateralis.
The degeneration following a lesion in the lumbar cord is in the ventro-lateral (antero-lateral)
tract, and is traceable up to the ventral part of the superior worm of the cerebellum ; thedorso-
lateral cerebellar tract ends more dorsally. also in the superior worm. Some degenerated fibres
pass through the corpus dentatum cerebelli into the dorsal part of the superior peduncle.

b. Destruction of tlie grey matter of tlie spinal cord. — This lesion can be experimentally
produced in the rabbit by compression of the aorta, lasting for about an hour (Ehrlich and
Brieger). The immediate result of the experiment is to cause necrosis of all the nerve-cells
in the lumbar region of the spinal cord, without immediately affecting the white matter or
the nerve-roots, a condition which is followed in the course of a few days by degeneration of
certain fibres, which may be assumed to be those which emanate from the necrosed cells.
If the animal is kept until this degeneration is well marked and is then killed and the
cord examined in sections, it is found that in the necrosed region and immediately above
it there is extensive degeneration in all the white columns of the cord, but least in the pos-
terior columns and in the posterior parts of the lateral columns, where the long tracts of con-
nection with the brain are situated. In sections taken higher up and well above the region
of necrosis this diffuse degeneration has disappeared, but there is well-marked degeneration
along the whole length of the cord in the tract of Goll and in the antero-lateral ascending
tract. It has been inferred, therefore, by Singer and Munzer that these tracts contain long
fibres which are derived from the cells of the grey matter (of the lumbar region).

c. Destruction of the cells of Clarke's column along a certain length of the cord is followed
by well-marked " ascending " degeneration in the dorso-lateral (direct) cerebellar tract (Mott).

RECENT LITERATURE.

Auerbach, 3j. , Zur Anatomic d. aufsteigenden degenerierenden Systeme des Ruckemnarks, Anat.
Anzeiger, 1890.

Bastian, H. Charlton, On the symptomatology of total transverse lesions of the spinal cord,
Medico-Chirurgical Transactions, vol. 73, 1890.

Bechterew, "W., Ue. d. Bestandtheile der Hinterstrdnge des Riickenmarks, Neurol. Centralbl.,
1885 ; Ueber einen besonderen Bcstandtheil der Seitenstrange des Riickenmarks und iiber den Faser-
ursprung der grossen avfsteigenden Triyeminusuurzel, Arch. f. Anat. u. Physiol., Anat. Abth. 1886 ;
Ueber die hinteren Nervenwurzeln, Hire Endigung in der grauen Substanz des Riickenmarks und ihre
centralc Fortsetzung im letzteren, Archiv f. Anat. u. Phys. , Anat. Abth., 1887 ; Le ccrveau de Vhommc
dans ses rapports, £c., Arch, slaves de biologic, 1887 ; Ueber die Pyramidenbahnen beim Menschen u.
d. Tkieren, $c., Neurol. Centralbl.. 1890.

Bechterew u. Hosenbach, Ueber die Bedeutung der Intervertebralganglien, Neurol. Centralbl..
1884.

Bertelli, Le sitton intermediaire ante'ricur de la moelle humaine dans la premiere annee de vie,
Extract in Arch. ital. de biol. xi., 1889.

Birge, E. A., Die Zahl der Ncrvenfasern und der motorlschen Ganglienzellcn im Riickenmark
des Froschcs, Archiv f. Anat. u. Phys., Phys. Abth., 1882.

Burckhardt, K. E,., Jfistologische Untersuchungen am Riickenmark der Tritonen, Arch. f.
mikrosk. Anat., Bd. xxxiv., 1889.

Colman, W. S., Notes on the minute structure of the spinal cord of a human fcelus, Journ. of
Anat. and Physiol., 1884.

Corning:, H. K., Ueber die Entwicklung der Substantia gelatinosa Rolandi beim Kaninchen,
Arch. f. mikrosk. Anat., xxxi., 1888.

Dickinson, On the changes in the nervous system which follow amputation, Journal of Anat. and
Physiol., 1868.

Dreschfeld, J., On changes in the spinal cord after amputation of limbs, Journ of Anat. and
Physiol., 1880; Riickenmark u. Gehirn i. e. Falle v. angeb. Mangel eines Vordcrarms, Yirch. Arch.
89, 1882.

Eding-er, L., Vorlesungen u. d. Bau der nervoscn Centralorgane, Leipzig, 1889 ; Ue. di-e Fort-
setzung der hinteren Ruckenmarkswurzeln zum Gehirn, Anat. Anzeiger, iv., 1889 ; Einiges Tom Verlauf
der Gefuhlsbahnen im centralen Ncrvensystemc, Deutsche medicin. Wochenschrift, 1890.

Ehrlich u. Brieger, Ueber die AusS'-haltunn des Lendenmarks, Zeitschr. f. klin. Medicin. vii. ,
1884.

RECENT LITERATURE. 35

Flechsig-, P., 1st die Tabes dorsalis eine " System- Erkrankung" 1 Neurol. Centralbl., 1890 (con-
tains remarks on the differentiation of the posterior columns in the spinal cord of the foetus).

France, E. P., On the descending degenerations which follow lesions of the gyrus marginalis and
gyrus fornicatus in monkeys, Philos. Trans. B., 1889.

Francotte, De la degenerescence ascendante sccondaire dufaisceau de Gowers, Bruxelles, 1889.

Fraser, On the pyramidal tracts of certain rodents, Dubl. Journ., Aug., 1889.

Friedlander u. Krause, F., Ueber Verdnderungen der Nerven it. des Riickenmarks n. Ampu-
tationen, Fortschr. der Medicin, 1886.

Gad, J., Ueber Centren und Leitungsbahnen im Ruckenmark des Frosches, Verhandl. der physiol.
Gesellsch. zu Berlin ; Arch. f. Anat. u. Phys., Phys. Abth., 1884.

G-aule, J. , Zahl u. Vertheil. der markhaltigen Fasern im Froschriickenmark, Sachs. Abhandl.,
Bd. xv., 1889.

Geb.ucb.ten, A. van, La structure des centres nerveux : la moelle epinivre et le cervelet, La
Cellule, vii., 1891.

Golgi, C., llecherches sur I'histologie des centres nerveux, Archives italiennes de biologic, iii. &
iv., 1883 ; Anat. Anzeiger, 1890.

Gotch, F., and Horsley, V., On the mammalian nervous system, its functions, and their locali-
sation determined by an electrical method, Phil. Trans., Vol. 182, B, 1891.

Gowers, "W. 3J., Diagnosis of diseases of the spinal cord, 1879 ; Diseases of the nervous system,
i., 1886 ; Bemei'kungen iiber die antero-laterale aufsteigende Degeneration im Rilckenmark, Neurolog.
Centralbl., No. 5, 1886 ; Weitere Bemerkungen iiber den aufsteigenden antero-lateralen Strang,
Neurolog. Centralbl., No. 7, 1886.

Guldberg-, He. d. Centralnervensystem der Bartenwale, Christiania, 1886.

Hadden, On a symmetrical degeneration of the spinal cord and medulla oblongata, Trans, of the
Pathol. Soc., 1882.

Hadden and Sherringrton, On a case of bilateral degeneration in the spinal cord, &c., Brain,
1886; The patholor/ical anatomy of a case of locomotor ataxy. <tc., Brain, 1888.

Hayem and Gilbert, Note sur les modifications du systeme nerveux chtz un ampute, Arch, de
pbysiol., 1884.

Helwegr, fitudien iiber den centralen Verlauf der vasomotorischen Nervenbahnen, Archiv f.
Psychiatrie, xix., 1887.

Herter, A study of experimental myelitis, Journ. of nervous and mental disease, 1889.

Herzen, A., et Lowentbal, N. , Trois cas de lesion medullaire au niveau de jonction de la
moelle epiniere et du bulbe rachidien, Archives de physiol., 1886.

Hill, A., Plan of the central nervous system, 1885.

Hoche, A., Beitrdge zur Kenntniss d. anatom. Verhaltfns d. inenscldichen Ruckenmarksiourzeln,
&c., Heidelberg, 1891.

Hofrichter, Ueber aufsteigende Degeneration des Ruckenmarkes, $c., Dissert. Jena, 1883.

Hollis, W. Ainslie, Researches into the Histology of the Central Grey Substance of the Spinal
Cord and Medulla Oblongata, Journal of Anat. and Physiol., 1883 and 1884.

Homen, E. A., Ueber secunddre Degeneration im verldngerten Mark und Riickenmark, Virchow's
Archiv, Bd. 88, 1882 ; Exper. Beitr. z. Pathol. u. pathol. Anat. d. Ruckenmarkes, Fortschr. d. Medicin,
1885 ; Die histol. Verdnderungen in d. periph. Nerven, d. Spinalganglien u. d. Riickenmarke
in Folge von Amputation, Neurol. Centralbl., 1888.

Horsley, V., Relation of posterior columns of cord to excito-motor area of cortex cerebri, Brain.
1886.

Joseph, M., Zur Physiol. der Spinalganglien, Neurol. Centralbl., 1887 ; Arch. f. Anat. u.
Physiol., 1887.

Kahler, O., Ueber d. Verdnderungen im Riickenmarke nach Compression, nebst einem d. secund.
Degeneration im Riickenmarke des Hundes betreffenden Anhang, Zeitschr. f. Heilkunde, iii., 1882;
Faserverlauf in den Hinterstrangen, Berliner klin. Wochenschr. , 1882; Ueber die Unheilbarkeit gew.
Riickenmarkserkrankungen, Pvag. med. Wochenschr., 1889 : Der Nervenapparat, In Lehrbuch der
Gewebelehre, von Dr. C. Toldt, 1888.

Kaiser, O., Die Functionen der Ganglienzellen des Halsmarkes, Haag, 1891 (contains a full
bibliography of the topography of the nerve-cells of the cord).

Kb'lliker, A. v., Zur feineren Anatomic des Centralnervensystems ; Zioeiter Beitrag : Das
Ruckenmark, Zeitschr. f. \rissen. Zoologie, 51, 1890.

Kronthal, P., Histol ogisches von den grossen Zellen in den Vorderhornern, Neurologisches
Centralbl., Jahrg. ix., 1889.

Lachi, P., Contrib. alia istogenesi d. nevrogliad. midollo spinalc del polio, Atti d. soc. tosc. d. sc.
nat. , xi., 1891 ; Contributo all' istogenesi del midollo spinale nel polio, Atti accad. med. chir. di
Perugia, 1889.

Lang-ley, J. N. , Recent observations on degeneration, and on nerve tracts in the spinal cord. A
critical account. Brain, 1886 (contains references to most important literature of the subject up to
that date).

Lang-ley and Griinbatim, On the degenerations resulting from removed of the cerebral cortex and
corpora striata in the dog, Journal of Physiol., xi., 1890.

Laura, J. B., Sur la structure de la moelle dpiniere, Archives italiennes de biologic, Tom I.,
1882.

Lavdowsky, M., Vom Aufbau d. Ruckenmarkes, Arch. f. mikr. Anat., Bd. 38, 1891.
Lenhossek, M. v., Ueber d. Verlauf d. Hinterwurzeln im Ruckenmark, Arch. f. mikr. Anat.,
Bd. 34, 1889 ; Ueber Nervenfasern in d. hinteren Wurzeln, welche a. d. Vorderhorn entspringen,
Anat. Anzeiger, 1890, also in the Proceedings of the Hungarian Academy of Sciences, vol. 19 ; Zur

D 2

86 RECENT LITERATURE.

Kenntniss der Ncuroglia des menschlichen Riickcnmarkcs, Verhandl. d. Anat. Gesellsch., 1891; Untcr-
suchungen iiber die Entivicklung der Markscheiden und den Faserverlauf im Riickenmark, Archiv. f .
mikrosk. Anat., Bd. xxxiii., 1889.

Lissauer. H., Beitrag zum Faserverlauf im Hinterhorn des menschlichen Ruckenmarks und zum
Verhalten desselben bei Tabes dorsalis, Archiv f. Psychiatrie, xvii., 1886 ; Ue. Verdnderungen d.
Clarke' 'schen Saule bei Tabes dorsalis, Fortsch. d. Medicin, 1889.

Lb'wenthal, N. , Contribution experimentale a V etude des atrophies secondaires du cordon
post^rieur et de la colonne de Clarke, Recueil zool. Suisse, T. iv. , 1886 ; La region pyramidale de la
capsule interne chez le chien et la constitution du cordon antero-lateral de la moelle, Revue medic, de
la Suisse romande, No. 9, 1886 ; Ue. d. Unterschied d. secund. Degeneration des Seitenstrangs nach
JJirn- u. Riickenmarksverletzungen, Pfliiger's Arch., 31, 1883 ; Des degenerations secondaires de la
moelle epiniere consecutives aux lesions experimentales medullaires et corticales, Dissert. , Geneve, 1885.

liiideritz, Ueber das Ruckenmarks -segment, Arch. f. Anat. u. Phys., Anat. Abth., 1881. •

Liustigr, A., Zur Kenntniss des Faserverlaufes im menschlichen Ruckenmarke, Sitzungsber. d.
Wiener Akad., Bd. 88, iii. Abth., 1883.

Marchi, V., Sulle degen. consec. alia estirpazione totale e parziale del ccrvelctto, Rivista sperim.
di freniatria, &c. , 1888.

March! e Alg-eri, S. degen. consec. a lesioni sperim. d, corteccia cercbrale. Rivista speriment. di
freniatria, 1887.

Mayser, P., Experim. Beitrdge zur Kenntniss d. Baues des Kaninchenruckenmarks, Arch. f.
Psychiatrie, Bd. vii. and Bd. ix.

Mott, F. "W. , Shape and size of the cells of Clarke's column, British Medical Journal, 1887 ;
Microscopical examination of Clarke's column in man, the monkey, and the dog, Journal of Anat.
and Phys., xxii., 1888 ; Bipolar cells of the spinal cord and their connections, Brain, 1890 ; Results of
hemisection of the spinal cord in monkeys, Phil. Trans., B., 1891.

Obersteiner, The Anatomy of the Central Nervous Organs, translated by A. Hill, London,
1890.

Odd! and Rossi, Sur les cours des voies afferentes de la moelle epiniere, <kc., Archives ital. de
biol., xv., 1891.

Pfitzner, W. , Ueber Wachsthumsbeziehungen zwischen Riickenmark und Wirbelkanal, Morphol.
Jahrb., 9, 1883.

Pitres, Recherches anatomo-cliniques sur les scleroses bilaterales de la moelle epiniere, d-c., Arch,
de Phys., 1884.

Popoff, N., Recherches s. I. structure des cordons posterieures, &c., Arch, de Neurologic, 1889.

Ramon y Cajal, Estructura de los centros nerviosos de las aves, Revista trimestr. de histologia,
1888 ; Contrib. al estudio de la estructura de la medula espinal, Ibid., 1889 ; Sur Torigine et les
ramifications des fibres nerveuses de la moelle embryonnaire, Anat. Anzeiger, 1890 ; Nuevas obser-
vaciones sobre la estructura de la medula espinal de los mamiferos, 1890 ; A quelleepoque apparaissent
les expansions des cellules nerveuses de la moelle epiniere du poulet ? Anatom. Anzeiger, 1890.

Ravenel, M., Die MassenverhdUnisse der Wirbelsaule u. des Riickenmarkes beim Menschen,
Zeitschr. f. Anat. u. Entw., ii.

Reid, R. W., The relations between the superficial origins of the spinal nerves from the spinal
cord and the spinous processes of the vertebrw, Journal of Anatomy, xxiii., 1889.

Renaut, J., La neuroglie et Vependyme, Arch, de Phys., 1882.

Reynolds, E. S., On changes in the nervous system after amputation of limbs, Brain, 1887
(includes good bibliography of this subject).

Ross, J., On the segmental distribution of sensory disorders. Brain, 1888.

Rossolimo, G-., Experimental researches into the question of the sensory and motor paths in the
spinal cord, Inaug. Diss., Moscow (Russian), Abstr. in Neurol. Centralbl., 1887, also in Arch, de
Neurol., vol. xxii., 1891.

Saint Remy, Q-., Recherches sur la portion terminalc du canal de Vependyme chez les vertebres,
Paris, Savy, 1887.

Sandmeyer, W., Ueber secunddre Degeneration nach Exstirpation motorischer Centra, Zeitschr.
f. Biologie, x., 1891.

Schafer, E. A., Report on lesions in brain and spinal cord of a macacque monkey, Journal of
Phys., 1883, and in Trans. Int. Med. Congress, 1881.

Schaffer, K. , Vergleichend-anatom. Untersuch. ii. Riickenmarksfaserung, Arch, f . mikr. Anat., Bd.
38, 1891.

Schultz, R., Zur Vacuolenbildung i. d. GanglienzeUen d. Ruckenmarks, Neurol. Centralbl., 1884.

Schultze, Beitr. zur Lehre v. d. secunddren Degeneration im Ruckenmarke des Menschen, tike. ,
Arch. f. Psychiatrie, xiv. ; Einige Bemerkungen ii. d. Mittheilung von Bechterew u. Rosenbach, <L-c.,
Neurol. Centralbl., 1884.

Sherrington, C. S., On secondary and tertiary degeneration in the spinal cord of the dog,
Journal of Phys., 1885 ; 'Note on two newly-described tracts in the spinal cord, Brain, Oct., 1886 ;
Nerve-tracts degenerating secondarily to lesions of the cortex cerebri, Journal of Physiology, 1889 ;
Note on bilateral degeneration in the pyramidal tracts resulting from unilateral cortical lesion, British
Medical Journal, Jan., 1890 ; Further note on degenerations following lesions of the cortex cerebri, Journ.
of Physio!., 1890 ; Outlying nerve-cells in the mammalian spinal cord, Phil. Trans., vol. clxxxi.

Siemerling-, Ue. tin gesetzmdssiges anatom. Verhalten der Wurzeln in d. verschiedenen Hohen d.
Ruckenmarks, Neurol. Oentralbl., 1886 (Monograph publ. by Hirschwald, Berlin, 1887).

Singrer, J. , Ueber secunddre Degeneration im Ruckenmarke des Hundes, Sitzungsberichte der
Wiener Akad., Bd. 84, iii. Abth., 1882; Ue. d. Veranderungen am Riickenmark nach zeitweiser
Verschliessung der Bauchaorta, Wiener Sitzungsb. , iii. Abth., 1887.

RECENT LITERATURE. 37

Singer u. Munzer, Beitr. z. Anatomic d. Centralnervensystem*;, insbesondere des Ruclcenmarkes,
Wiener Denkschr. Ivii., 1891.

Spitzka, E. C., The comparative anatomy of the pyramidal tract, Journal of comparative
medicine and surgery, New York, 1886 ; Kurze Notiz die Lumbalanschwettung des Ruckenmarks betr.,
Neurol. Centralbl., 1885.

Spronck, C., Contrib. a I 'etude experim. des lesions de la moelle epiniere determines par Vanemie
passagere de cet organe, Arch, de phys. norm, et pathol., 1888.

Steinlechner-Gretschischnikoff, Alexandra, Ueber den Ban des Ruckenmarks bei Mikro-
cephalen, Arch. f. Psychiatric, Bd. xvii., 1886.

Striimpell, Beitr. z. Pathologic des Rilckenmarkes, Arch. f. Psychiatric, x. and xii.

Takacs, A., Ueber den Verlauf der hinteren Wurzelfasern im Riickenmark und den Aufbau
der wcissen Substanz am hinteren Abschnitte des Rilckenmarks, Neurolog. Centralbl., 1887.

Tooth, Howard, A contribution to the path, anatomy of the spinal cord, St. Earth. Hosp. Reports,
vol.*21 ; Note on the antero-lateral ascending tract, St. Earth. Hosp. Reports, vol. 23 ; Gulstonian
Lectures on Degenerations of the spinal cord, 1889.

Unverricht, Ueber doppclte Kreuzung ccrebrospinaler Leitungsbahnen, Neurol. Centralbl., 1890.

Vejas, P., Ein Beitrag z. Anat. u. Physiol. der Spinalganglien, Miinchen, 1883.

Vignal, W., Sur le developpcment des elements de la moelle des mammiferes, Archives de Physiol.,
1884.

Virchow, H., Ueber Zellen in der Substantia c/elatinosa Rolandi, Neurol. Centralbl., 1887;
Ueber das Riickenmark der Anthropoidtn, Anatom. Anzeiger, iii., 1888.

Wagrner, J. , Zur Anatomic des Ruckenmarks und der Medulla oblongata, Centralbl. f. Nerven-
heilkunde, 1886.

"Waldeyer, "W., Ueber d. Verlauf d. hinteren Nervenwurzeln, Sitzungsb. d. Gesellsch. naturf.
Freunde, Berlin, 1889 ; Ueber einige ncuere Forschungen im Gebiete der Anatomic d. Centralnerven-
systems, Deutsche mecl. Wochenshr., 1891 ; Das Gorilla-Riickenmark, Abhandl. d. Konigl. Preuss.
Akad. d. Wissensch., 1888.

Weig-ert, C., Bemerkunyen it d. Neurogliageriist des menschlichen Centralnervensystems, Anat.
Anzeiger, 1890.

38 THE MEDULLA OBLONGATA AND PONS VAROLII.

THE BRAIN OB ENCEPHALON.

The brain or encephalon comprises the medulla oblongata and pons Varolii, the
cerebellum, the mid-brain, and the cerebrum. The medulla oblongata (fig. 28, D) is
the part continuous with the spinal cord ; it is the lowest part of the encephalon,
and rests against the basilar process of the occipital bone. The pons Varolii (c) is
a direct continuation upwards and forwards of the medulla oblongata, but the name
also includes the transversely coursing fibres of the middle cerebellar peduncle. The
cerebellum (B) occupies the posterior fossa of the cranium. Its central part forms the
dorsal boundary of a space, which is bounded ventrally by the dorsal surface of the
medulla oblongata and pons Yarolii, and which is named the fourth ventricle of the

Fig. 28. — PLAN IN OUTLINE OP THE EN-
CEPHALON, AS SEEN FROM THE KIQHT
SIDE. 1

The parts are represented as separated
from one another somewhat more than
natural so as to show their connections.
A, cerebrum ; e. fissure of Sylvius ; B,
cerebellum ; C, poiis Varolii ; D, medulla
oblongata ; a, peduncles of the cerebrum ;
b, c, d, superior, middle, and inferior
peduncles of the cerebellum ; the parts
marked a, I, form the isthmus ence-
phali.

brain. The cerebellum is con-
nected by peduncles below with
the medulla oblongata, above with
the cerebrum, and in the middle
with the pons Varolii (c). The
mid-brain is continued from the
pons Varolii and comprises the two crura of the cerebrum (a), which are surmounted
in man and mammals by two pairs of tubercles named the corpora quadrigemina (&),
but in oviparous vertebrates by one pair only, then named the corpora bigemina or optic
lobes, The cerebrum (A) includes all the remaining and by far the largest part of
the encephalon. It is united with the parts below by the mid-brain, which forms a
comparatively narrow and constricted portion or isthmus. The cerebrum is mainly
composed of the large convoluted cerebral hemispheres, and within it are the third
and two lateral ventricles. It occupies the vault of the cranium, the anterior and
middle cranial fossae, and the superior fossae of the occipital bone. The cerebral
hemispheres are united together by a large commissure termed the corpus callosum,
and by smaller commissures (anterior, middle, and posterior).

THE MEDULLA OBLONGATA AND PONS VAROLII.

EXTERNAL CHARACTERS.

The medulla oblongata or spinal bulb (bulbus rhachiticus, Meckel) is continuous
below with the spinal cord, on a level with the lower margin of the foramen magnum.
Its upper limit is marked off on the ventral aspect from the pons Varolii, into which it
is continued above, by the lower margin of the mass of transverse fibres which unite
the two hemispheres of the cerebellum ; its ventral surface rests in the basilar groove

THE MEDULLA OBLONG ATA. 39

of the occipital bone, its dorsal or posterior surface is directly continued into that
of the pons, and lies in the fossa named the vallecula between the hemispheres of

*^«K. ^«. .«««—* , ~, ~ — v — — . — ..v.v , " , ^*v«*Vi*tj ""^*j , v/j corpora (juadrigeinina and pineal
+ , the fourth ventricle ; 7, pons Varolii ; 8, medulla oblongata ; 9, cerebellum ; i, the olfactory

t.Kfi -ricrlrf. nnt.ip nprvp • TTT rio-Vif. tViiivl nprvp

Fig. 29. — RIGHT HALF OF THE BRAIN DIVIDED BY A VERTICAL ANTERo-PObTEKicm SECTION (from various
sources and from nature x>. (Allen Thomson. ) J

] , 2, 3, 3a, 36, are placed on convolutions of the cerebrum ; 4, the fifth ventricle, and above it the
divided corpus callosum ; 5, the third ventricle ; 5', pituitary body ; 6,
gland ; + , the fourth ventricle ; 7, pons Varolii ; 8, me n
bulb ; ii, the right optic nerve ; in, right third nerve.

the cerebellum. From its front and sides the sixth to the twelfth cranial nerves issue,
while the fifth nerve emerges from between the commissural fibres of the pons.

The term medulla oblongata. as employed by Willis and Vieussens. and by those who
directly followed them, included the crura corebri and pons Varolii, as well as that part to
which by Haller first, and by most subsequent writers, this term has been restricted.

Fig. 30. — VIEW OF THE ANTERIOR SURFACE OF THE PONS VAROLII

AND MEDULLA OBLONGATA, WITH A SMALL PART OF THE SPINAL
CORD ATTACHED.

a, a, pyramids ; b, their decussation ; c, c, olives ; d, d,
restiform bodies ; e, external arciform fibres, curving round the
lower end of the olive ; /, fibres described by Solly as passing
from the anterior column of the cord to the cerebellum ; y,
anterior column of the spinal cord ; h, lateral column ; p,
pons Varolii ; i, its upper fibres ; v, v, roots of the fifth pair of
nerves.

The combined mass of the medulla oblongata
and pons has an oblong or rhomboidal form, being
expanded in the middle, where it is continuous
with the crura cerebelli, and tapering towards the
spinal cord below and the mid -brain above. The
transversely coursing fibres of the cerebellum pro-
duce a considerable prominence (tuber annulare) on
the ventral surface of the upper or pontine part of the
mass ; these fibres are arched upwards so as largely
to conceal the crura cerebri from the ventral aspect.

The length of the medulla

oblongata from the lower part of the decussation of the pyramids to the pons is

40 THE MEDULLA OBLONGATA AND. PONS VAROL1I.

nearly an inch (20 to 24 mm.), its greater breadth is about three-fourths of an inch
(17 to 18mm.) ; its thickness, from before backwards, is rather less (15 mm.). In
the lower part where it joins the spinal cord, its diameters differ but little from those
of the cord. The pons Varolii is about an inch long and rather more than an inch
broad ; it is considerably thicker than the medulla oblongata.

The anterior and posterior median fissures which partly divide the spinal cord
are continued into similar fissures in the medulla oblongata. The anterior fissure
terminates immediately below the pons in a recess, the foramen cwcum of Vicq
d'Azyr ; it is partly interrupted below by the decussating bundles of the pyramids ;
the posterior fissure is continued upwards to about the middle of the bulb, it ceases
at the lower end of the fourth ventricle.

The structure of the medulla oblongata and pons will be most easily made clear
by tracing the several parts of the spinal cord upwards.

In doing this it will be found that the relative position and extent of many of
the parts are gradually altered, and that other parts which are not, so far as is known,
represented in the spinal cord, become interpolated between those which are there
met with. It will further be found that the change of relative position of the parts
is largely owing to two causes. In the first place the sudden passage of large
bundles of medullated fibres from the posterior pare of the lateral column of the cord
to the opposite side of the anterior median fissure appears to break up to a great extent
the grey matter of the anterior horn, which is traversed by the bundles. In the second
place the opening up of the central canal and separation of the lips of the posterior
median fissure bring the grey matter to the surface in the fourth ventricle, whilst the
posterior horn is coincidently shifted to the side, much in the same way as it would
be if a median incision were made from the posterior surface of the spinal cord into
the central canal, and the two lateral halves were then turned outwards so that the
sides of the posterior median fissure became the posterior surface of the cord.

The lines along which the cranial nerve-roots issue from the sides of the bulb
mark the surface of the latter off into three chief columns on either side, which may

Fig. 31. — SECTION OF UPPER END OF SPINAL CORD AT THE JUNCTION
WITH THE MEDULLA OBLONGATA. (After Lockhart Clarke.)

/, anterior; fp, posterior fissure ; p, end of decussation of pyramids ;
Cla, CIp, anterior and posterior roots of first cervical nerve ; XI, root
of spinal accessory nerve ; c, central canal.

be termed dorsal, lateral, and ventral respectively. Thus
the spinal accessory or eleventh cranial nerve (figs. 32, 34,
35, XI) begins to take origin as far down as the lower
end of the cervical region of the cord where its roots issue

from the side of the cord, and lateral to the posterior roots of the cervical nerves
(fig. 31). At the upper end of the cervical region, however, they are approached by
the line of the posterior roots, and some of their bundles arise in conjunction with
the posterior roots of the first and sometimes of the second cervical nerve. They are
succeeded by the bundles of the vagus root, and these again by those of the glosso-
pharyngeal. At the junction of the pons with the medulla oblongata the seventh
nerve also is seen issuing along the same line, and still higher the large root of the
fifth is given off from the lateral aspect of the pons. The line of exit of this
series of nerve-roots is marked below by a shallow sulcus, but if traced upwards
it will be seen that the sulcus is obliterated or nearly so before long, so that
the issuing series of nerve-roots alone serves to mark its position. As it passes
upwards it becomes gradually diverted outwards ; so that opposite the place where
the central canal opens into the calamus scriptorius of the fourth ventricle, the line
iu question has left the posterior surface and in the rest of its course runs along

STRUCTURE OF THE MEDULLA OBLONGATA.

.4.1

the lateral surface of the bulb. Towards the upper end it passes near the pos-
terior margin of an oval prominence on the surface of the bulb termed the
olivary body or lower olive (0), but is separated from that prominence by a tract
of longitudinal fibres. In transverse sections of the lower part of the medulla
Fig. 32. — VIEW PROM BEFORE OF THE

MEDULLA OBLONGATA, PONS VAROLII,
CRURA CEREBRI, AND OTHER CENTRAL
PORTIONS OK THE ENCEPHALON. (Allen

Thomson.) NATURAL SIZE.

On the right side the convolutions of
the central lobe or island of Reil have
been left, together with a small part of
the anterior cerebral convolutions : on
the left side these have been removed by
an incision carried between the thalamus
opticus and the cerebral hemisphere.

1', the olfactory tract cut short and
lying in its groove ; II, the left optic
nerve in front of the commissure ; II',
the right optic tract ; Th, the cut surface
of the left thalamus opticus ; C, the
central lobe or island of Reil ; Sy, fissure
of Sylvius ; x x , anterior perforated
space ; c, the extei'nal, and i, the internal
corpus-geniculatum ; h, the hypophysis
cerebri or pituitary body ; tc, tuber
cinereum with the infundibulum ; «,,
one of the corpora albicantia ; P, the
cerebral peduncle or crus ; III, close to
the left oculo-motor nerve ; x , the
posterior perforated space.

The following letters and numbers refer
to parts in connection with the medulla
pblongata and pons. PV, pons Varolii ;
V, the greater root of the fifth nerve ; + ,
the lesser or motor root ; VI. the sixth
nerve ; VII, the facialj VIII, the audi-
tory nerve ; IX., the 'glossopharyngeal ;
X, the pneumogastric nerve ; XI, the
spinal accessory nerve ; XII, the hypo-
glossal nerve ; C I, the suboccipital or
first cervical nerve ; p a, pyramid ; o,
olive ; d, anterior median fissure of the
spinal cord, above which the decussation
of the pyramids is represented ; c a,
anterior column of cord ; r, lateral tract
of bulb continuous with c I, the lateral
column of the spinal cord.

oblongata (fig. 33) it is seen that the bundles of fibres of these nerve-roots traverse
the substance of the bulb to reach a group of nerve-cells in the grey matter near
the central canal and thus mark off a somewhat oval area on each side at the pos-
terior part of the section. This area is termed by Flechsig the posterior^ area of the
medulla oblongata, and the tracts of white fibres which can be traced, as will be
immediately noticed, upon the surface of this part, may therefore -be conveniently
termed its posterior columns. They correspond in position to the posterior columns
of the spinal cord.

The line of origin of the anterior roots of the spinal nerves, although not marked
in the spinal cord by a distinct furrow like that whence the posterior roots issue, yet
when traced upwards into the bulb, deepens into a well-marked longitudinal groove
which is continued almost vertically as far as the lower border of the projecting
mass of the pons. In its upper part this groove separates the olivary pro-
minence from the prominence of the pyramid. Just below the olive it is often
obliterated for a certain part of its course by a band of transverse fibres. The root-
bundles of the hypoglossal nerve (figs. 32, 33, 34, XII) pass out from this furrow,

42

THE MEDULLA OBLONGATA AND PONS VAKOL1I.

and those of the sixth nerve emerge in the same line with it but at the lower border
of the pons Varolii. In transverse sections of the medulla oblongata and pons these
root-bnndles may be traced back through the substance of the organ to a group or
column of nerve-cells situated in a portion of grey matter close to the antero-lateral
side of the central canal in the lower closed part of the bulb (fig. 43), and close to
the middle of the fourth ventricle in the upper opened-out part (figs. 44, 45). This

/.c

Fig. 33. — SECTION ACROSS THE MKDULLA OBLONGATA A LITTLE BELOW THE POINT OF THE CALAMUS

SCKIPTORIUS. (Lockhart Clarke.)

c, central canal ; /, anterior median fissure ; f.g, funiculus gracilis ; f.c, funiculus cuneatus ;
t.R., tubercle of Rolando ; o, olivary body ; a.p.. pyramid ; XI, XII, spiral accessory and hypoglossal
nerves ; XI', XII', their nuclei.

Fig. 34. — VIEW OP THE MEDULLA OBLONGATA, PONS VAROLII, CRURA CEREBHI, AND CENTRAL PARTS OP

THE ENCEPHALON FROM THE RIGHT SIDE. (Allen Thomson.)

The corpus striatum andthalamus opticushave been preserved in connection with the central lobe and
crura cerebri, while the remainder of the cerebrum has been removed.

St, upper surface of the corpus striatum ; Th, back part of the thalamus options (pulvinar) ; C.
placed on the middle of the five or six convolutions constituting the central lobe or island of Reil, the
cerebral substance being removed from its circumference ; Sy, fissure of Sylvius, from which these
convolutions radiate, and in which are seen the white strife of the olfactory tract ; I, the olfactory tract
divided and hanging down from the groove in the Convolution which lodges it ; II, optic nerves a little
way in front of the commissure ; a, right corpus albicans with the tuber cinereum and infundibulum in
front of it ; h, hypophysis or pituitary body ; e, external, and i, internal corpus geniculatum at the
back part of the optic tract ; P, peduncle or crus of the cerebrum ; III, right oculo-motor nerve ; p,
pineal gland ; q, corpora quadrigemina ; IV, trochlear nerve rising from v, the valve of Vieussens.

The following numbers and letters refer chiefly to parts in connection with the medulla oblongata and
pons. V, placed on the pons Varolii above the right nervus trigeminus ; s, the superior, in, the middle, and
in, the inferior peduncle of the cerebellum cut short ; VI, the sixth nerve ; VII, facial nerve ; VIII.
auditory nerve ; IX, the glosso-pharyngeal nerve ; X, placed opposite to the cut end of the pneumo-
gastric nerve ; and XI, the uppermost fibres of the spinal accessory nerve ; XII, the hypoglossal nerve ;
p a, pyramid ; o, olive ; a r, arciform fibres ; r, restiform body ; tr, tubercle of Rolando ; c a, anterior,
c p, posterior, and c I, lateral columns of the spinal cord ; C I, C i, anterior and posterior roots of the
first cervical nerve.

STRUCTURE OF THE MEDULLA OBLONG ATA.

portion of grey matter is continuous below with part of the anterior horn, and the
roots of the hypoglossal and sixth nerve appear to correspond generally with the anterior
roots of the spinal nerves. In traversing the substance of the bulb they mark off an
anterior area, wedge-shaped in transverse section, which is placed between them and
the anterior median fissure. This area is on the surface marked by the prominence
known as the pyramid or anterior pyramid, which corresponds in position (but only
to a small extent iu the fibres of which it is composed) with the anterior column of
the spinal cord. The remainder of the transverse section of the bulb, after the
posterior and anterior areas are deducted, lies between the line of nerve-root bundles
of the hypoglossus and sixth on the one side, and that of the successive bundles of the
spinal accessory, vagus, glosso-pharyngeal, and seventh on the other. This is termed
by Flechsig the lateral area, and on the surface it is marked by a continuation
of part of the lateral column of the cord, and by the prominence of the lower olive
already alluded to.

"We may now proceed to describe in detail the several parts which appear upon
the surface of the bulb in the three regions thus marked off by the two sets of
nerve-roots, commencing with the posterior area. t

Posterior area. It will be remembered that in the upper region of the
spinal cord a small portion of the whole posterior column is marked off from the rest
by a well-developed pia-matral septum, and is indicated on the surface by a distinct

Fig. 35. — POSTERIOR AND LATERAL VIEW OF THE

MEDULLA OIJLONGATA, FOURTH VENTRICLE AND
5IESENCEPHALON. (E.A.S.) NATURAL SIZE.

The cerebellum and inferior medullary velum,
and the right half of the superior medullary
velum, have been cut away, so as to expose the
fourth ventricle.

p.n., line of the posterior roots of the spinal
nerves ; p.m.f., posterior median fissure ;
f.g., tuniculus gracilis ; cl., its clava; f.c.,
funiculus cuneatus ; f.R-, funiculus of
Rolando; r.l>., restiform body; e.g., lower end
of the fourth ventricle (calamus scriptorius) ; I,
section of the lingula or tsenia ; part of the
choroid plexus is seen beneath it ; l.r., lateral
recess of the ventricle ; sir, strice acusticse ; i.f.,
inferior (posterior) fovea ; s.f., superior (anterior)
fovea ; between it and the median sulcus is the
funiculus teres ; cbl, cut surface of the left
cerebellar hemisphere ; n.d., central grey matter
(nucleus dentatus) seen as a wavy line ; s.m.v.,
superior (anterior) medullary velum ; Ing, lin-
gula ; s. c.p. , superior cerebellar peduncle cut
longitudinally ; cr, combined section of the
three cerebellar peduncles (the limits of each are
not marked) ; c.q.s., c.q.i., corpora quadrigemina
(superior and inferior) ; fr, frsenulum veil ; /,
fibres of the fillet, seen on the surface of the teg-
mentum ; c, crusta ; l.g. , lateral groove ; c g. i. ,
corpus geniculatum internum ; th, posterior part
of thalamus ; p, pineal body. The Roman num-
bers indicate the corresponding cranial nerves.

longitudinal prominence bounded later-
ally by a shallow groove. The portion
thus marked off is the postero-mesial

column (tract of Goll), and the prominence, which is continued up into the medulla
oblongata, becomes there still better marked, arid is known as the funiculus gracilis
(fig. 35, f.(f). This, as it is traced upwards, especially as the fourth ventricle is
approached, broadens out into an expansion termed the clava (cl), and as the ventricle
opens out the clavas of opposite sides diverge and form the lateral boundary to the

obi

44

THE MEDULLA OBLONGATA AND PONS VAROLII.

ventricle in its lower part. Above, the clavse are tapered off and soon become no
longer traceable.

The funiculi graciles with their clavas are sometimes described as foa posterior, pyramid*.

Between the postero-mesial column and the postero-lateral groove from which
the posterior roots of the cervical nerves pass out there is found in the upper part of
the cord a single distinct column, viz., the postero-lateral column (tract of Burdach).
This is also prolonged into the medulla, and also like the funiculus gracilis expands
as it is traced upwards : it is here known as the funiculus cuneatus. Outside this
funiculus cuneatus and between it and the line of roots of the spinal accessory
another longitudinal prominence is caused by the fact that the substantia gelatinosa
of Rolando begins near the lower end of the bulb to project towards the surface
as a distinct funiculus, narrow below but broadening as it is traced upwards, where it
forms a considerable eminence known as the tubercle of Rolando. The longitudinal
prominence which passes up into it, is termed therefore by Schwalbe, the funiculus
of Rolando (bg. 35, /.#.).

The funiculus of Rolando is termed by Henle the lateral cuneate funiculus.

On a level with the adjoining clava of the funiculus gracilis, the enlarged part of the
cuneate funiculus also, like that, exhibits a slight eminence, which is best marked in children,
and has been termed the cuneate tubercle (Schwalbe).

In the upper part of the medulla oblongata, the cuneate funiculus is concealed by
a set of fibres (external arched or arcuate fibres) which issue from the anterior median

Fig. 36. — DISSECTION OP THE MEDULLA OBLONGATA AND PONS

SHOWING THE COURSE OF THE PTRAMIDAL TRACTS IN THEM.

(Allen Thomson.)

P, pons Varolii ; p, the pyramids, the upper part of the
right one has been cut away ; p', the fibres of the left
pyramid, as they ascend through the pons, exposed by the
removal of the superficial transverse fibres ; p" is placed on
some deeper transverse fibres of the pons on the right side,
below the divided fibres of the right pyramid ; a, left
anterior column of the cord, its median part passes upwards
into the outer part of the pyramid, the remainder dips
beneath the pyramid and olivary body ; o. olivary body ; o',
the continuation of part of the lateral column ascending
through the pons and exposed by the removal of a small
portion of the deeper transverse fibres ; o", some of the
same fibres divided by a deeper incision on the right side ;
I, I', the lateral columns of the cord ; x , their deeper parts
passing by decussation into the pyramids ; r, direct cere-
bellar tract passing from the lateral column into the inferior
peduncle of the cerebellum, or restiform body ; r', fasciculus
passing from the anterior column to the same ; ft, deep
longitudinal fibres derived from the anterior and lateral
columns of the cord.

B, explanatory outline of the section of the spinal cord,
a, anterior columns ; p, posterior ; I, lateral.

fissure and passing laterally over the surface of the pyramid and olive, turn upwards
to join the restiform body. There is also a narrow strand of fibres from the lateral
column of the cord, marked by its white appearance, which joins this tract of oblique
fibres just above the level of the tubercle of Rolando. This is the dor so-lateral (direct)
cerebellar tract which has been already noticed in the description of the spinal cord.
These obliquely crossing fibres turn upwards as they cross the funiculus of Rolando,
and appear to blend with that column and with the cuneate funiculus. They do
not, however, actually blend with them, but are reinforced by a large number of fibres
coming from the opposite side of the bulb (see p. 52, fig. 44), and the whole mass
of fibres thus produced forms a rounded, prominent cord, the corpus restiforme, or
rope-like body (fig. 36, r), which passes directly into the corresponding hemisphere
of the cerebellum, constituting its inferior peduncle.

ANTERIOR AREA. 45

Lateral area. — The lateral column of the spinal cord appears, on the surface, to
be directly continued upwards into the lateral area of the medulla oblongata. In
reality, however, a considerable tract of the white fibres — that which in the spinal
cord we have noticed as the lateral pyramidal tract — is found, at the upper end of
the spinal cord, to cross obliquely in stout bundles through the grey matter of
the anterior horn, and across the anterior median fissure to the other side of the bulb,
where it forms the mesial and larger part of the pyramid (figs. 36, 37). The rest of
the lateral. column can be traced vertically upwards (with the exception of the dorso-
lateral cerebellar tract which passes backwards into the restiform body) as far as the
lower end of the olive where its longitudinally coursing fibres become concealed by
this prominence and by the arched fibres already noticed.

The olivary body or lower olive (figs. 32, 34, 36, o) is, as its name implies, an
olive-shaped prominence, which lies in the upper part of the bulb, immediately above
the apparent termination of the lateral column, and extending nearly as far as the
lower border of the pons, being only separated from this by a deep groove in which
is sometimes a small band of arched fibres. The line of exit of the hypoglossal
nerve-roots lies on its inner or mesial border, that of the accessory, vagus and glosso-
pharyngeal roots along its outer side, but the latter are separated from it by a groove
in which longitudinal fibres prolonged from the ventro-lateral cerebellar tract can be
seen. Sometimes there is a small longitudinal tract running along its inner border
also, and in such case, with the arched fibres above and below, the olive appears to
be entirely enclosed by a fibrous strand, which has sometimes been described as its
capsule (siliqua olivcn). This name is, however, more applicable to a layer of fibres
which immediately surrounds the dentate nucleus of the olive (see note on p. 56,
and fig. 44, s.o.). The longitudinal tracts on either side of the olive are often con-
cealed in great measure by the arched fibres, which may form a complete superficial
layer over the olive, and indeed over the whole anterior and lateral surface of this
upper part of the medulla oblongata.

Anterior area. — The anterior columns of the cord, although on superficial
inspection they appear to be prolonged into the pyramids of the bulb, are so

Fig. 37. — SECTION OP THE MEDULLA OBLONGATA AT THE MIDDLE OF
THE DECUSSATION OF THE PYRAMIDS. (Jjockharb Clarke.)

/, anterior; f.p. , posterior fissure ; a.p., pyramid ; a, remains
of part of anterior cornu, separated by the crossing bundles from
the rest of the grey matter ; I, continuation of lateral column of
cord; R, continuation of substantia gelatinosa of Rolando; p. c.,
continuation of posterior cornu of grey matter ; f.g., funiculus
gracilis.

only to a small extent. For the lateral pyramidal

bundles, crossing the anterior median fissure from the

lateral column, are continued upwards close to that

fissure, and unite with the comparatively small anterior

pyramidal bundle to constitute the prominence known

as the pyramid (anterior pyramid). The prolongation

upwards of the rest of the anterior column of the cord lies deeply, being altogether

concealed from view by the pyramids.

The pyramids (figs. 30, a, 32, pa), are more prominent above than below.
They are bounded mesially by the anterior median fissure, and laterally by the
olivary bodies, being separated from these by the groove before mentioned, from
which the roots of the hypoglossal nerve issue. At their upper end they are
constricted, and become more completely separated from the rest of the medulla
oblongata. They are here very frequently crossed by a band of arched fibres, the

46

THE MEDULLA OBLONGATA AND PONS VAROLII.

pont'iculus of Arnold. Each pyramid then enters the substance of the pons in one
large bundle, which soon breaks up into several bundles, and these may be traced
through the pons into the corresponding peduncle of the cerebrum.

The decussation of the pyramids is the name given to the obliquely crossing
bundles of the lateral pyramidal tract which are seen in the anterior median fissure
at the lower part of the medulla oblongata. The extent to which the decussation is
visible varies considerably in different individuals ; for in some the bundles take a
deeper, in others a more superficial course. Further, in some cases a larger share
than usual of the longitudinal fibres of the pyramids passes down in the anterior
pyramidal tract and a correspondingly smaller share in the lateral pyramidal tract.
And since the anterior tract, which in the pyramid is external to the lateral tract,
does not cross in the medulla oblongata but merely passes obliquely at its lower end
to attain the side of the anterior median fissure, the decussation in these cases is of
less extent. On the other hand, in rare cases, the whole of the fibres of the pyramid
may cross over at the lower part of the bulb and become lateral pyramidal tract,
in which case the anterior or uncrossed tract is wanting in the cord, and the
bulbar decussation is very well marked. All transitions are found between these
two conditions (see p. 24).

The pons Varolii forms a prominence marked by transverse fibres above and in
front of the medulla oblongata, and between the lateral hemispheres of the

a\

Fig. 38. — TRANSVERSE SECTION THROUGH LOWER PART OF PONS VAROLII. (After Stilling and Schwalbe.)
The description of this figure is given on p. 61.

cerebellum (fig. 38) ; at the sides its transverse fibres are gathered together into
a compact mass, which passes into the cerebellum, and is named the middle cms
or middle peduncle of the cerebellum. On its ventral surface the pons has a shallow
median groove along which the basilar artery runs, and it is perforated by small
branches of the artery. The groove is in some measure due to the circumstance
that the pyramids of the medulla oblongata are continued up through the pons with
a slightly divergent course, and thus produce a prominence on either side of the
middle line, covered, however, by the superficial transverse fibres.

THE FOURTH VENTRICLE. 47

The pons consists ventrally of transverse cerebellar fibres, between which
the longitudinal fibres prolonged upwards from the medulla oblongata pass ;
together with a large intermixture of grey matter. The superficial fibres on the
ventral surface (fig. 30, p) are transverse in their general direction, but while the
middle fibres are exactly transverse, the lower set ascend slightly, and the superior
fibres (fig. 30, i), which are the most curved, descend obliquely to reach the eras
cerebelli on each side ; some of the upper fibres cross obliquely the middle and
lower ones, so as to conceal them at the sides. When the superficial transverse
fibres are removed, the prolonged fibres of the pyramids come into view (fig. 36) ;
these, as they ascend through the pons, are separated into smaller bundles,
intersected by other transverse white fibres, which, with those upon the surface,
are all continued into the middle peduncle of the cerebellum.

At the lower part of the pons, dorsal to the fibres from the pyramids, is a
special set of transverse fibres (fig. 38, /), named the trapezium (corpus trapez-
oides) — so called because in most mammals, in which the inferiorly situated fibres of
the pons are less developed and the pyramids are small, these transverse fibres
partially appear on the surface in an area of a somewhat four-sided shape. Laterally
they curve round a collection of grey matter, called the superior olivary nucleus
(fig. 38, 0.s.), and probably many of them are connected with its cells. They then
course lateralwards, across the bundles of the facial nerve-roots (F77), and ventral
to the upward prolongation of the substantia gelatinosa of the tubercle of Rolando
and the bundles of fibres belonging to the ascending root of the fifth nerve (#.F),
and appear to become connected with the accessory auditory nucleus (p. 55) and
with the ventral root of the auditory nerve, of which, according to Flechsig, the
trapezium forms a cerebral commissure.

The fourth ventricle. — The external characters of the medulla oblongata and
pons may be completed by a description of those parts which enter into the
boundaries of the fourth ventricle. This is the space into which the central canal
of the cord, after becoming somewhat enlarged and cleft-like, opens out superiorly
(fig. 39). The opening-out seems as if effected by the divergence of the funiculi
graciles et cuneati on either side at an acute angle. These funiculi, which form the
lateral boundaries of the lower part of the ventricle, bend round laterally at about
the middle (in length) of the medulla oblongata, so that the ventricle, which is at
first narrow, rapidly broadens. Opposite the middle peduncle of the cerebellum it
has attained its greatest width. From this point its upper part again narrows, con-
verging gradually above to be continued into the comparatively narrow Sylvian
aqueduct. The ventricle is therefore irregularly lozenge- or diamond-shaped, and
is sometimes named fossa rhomboidalis. The pointed lower end of the ventricle
has the shape of a writing pen, and is termed the calamus scriptorius (fig. 39, c.s.}.
At its widest part the fourth ventricle is continued for a short distance on either
side between the cerebellum and bulb where these come in contact, in the form
of the pointed lateral recess (Lr.). The lateral boundaries of the ventricle
are, in its lower or medullary part, the clavae of the funiculi graciles, the funiculi
cuneati, and the restiform bodies ; in its upper half the superior peduncles of the
cerebellum (fig. 39, s.c.p.}. These pass gradually to the roof of the ventricle as
they extend upwards. They are at first separated from one another by a tolerably
wide interval which, however, gradually narrows near the end of the ventricle,
the two crura of opposite sides there approaching one another, and their margins
coming in contact. Roof of the ventricle. The triangular interval between
the two crura is bridged over by a lamina of white matter marked across with
grey streaks. This is the superior medullary velum or valve of Vieussens (fig.
39, s.m.v.), and, with the crura, forms the roof or dorsal boundary of the upper
part of the fourth ventricle. The white substance of which it is mainly composed

48

THE MEDULLA. OBLONGATA AND POXS VAROLII.

is marked dorsally by three or four flat transverse grey laminse, Avith intervening
sulci, which together constitute the lingula (fig. 39, Ing}. This is continued
laterally into the grey cortex of the cerebellum, while the subjacent white substance
of the velum is in direct continuity with the central white matter of the cerebellum,

cbl

S.CJ)

Fig. 39. — POSTERIOR AND LATERAL VIEW OP

THE MEDULLA OBLONGATA, FOURTH VENTRICLE
AND MESENCEPHALON. (E. A. S. ) NATURAL
SIZE.

The cerebellum and inferior medullary velum,
and the right half of the superior medullary
•velum, have been cut away, so as to expose the
fourth ventricle.

p.n., line of the posterior roots of the spinal
nerves ; p.m./., posterior median fissure ; f.g.,
funiculus gracilis ; cZ. , its clava ; f.c. , funiculus
cuneatus ; /. R. , funiculus of Rolando ; r. 6. ,
restiform body; c.s. , lower end of the fourth
ventricle (calamus scriptorius) ; I, section of the
ligula or twnia ; part of the choroid plexus is
seen beneath it ; J.r., lateral recess of the
ventricle ; str, striae acusticae ; ?'./., inferior
(posterior) fovea ; «./., superior (anterior)
fovea ; between it and the median sulcus
is the funiculus teres ; cbl, cut surface of
the left cerebellar hemisphere; n.d. , central
grey matter (nucleus dentatus) seen as a wavy
line ; s.m.v., superior (anterior) medullary
velum; Iny, lingula ; s.c.p., superior cerebellar
peduncle cut longitudinally ; cr., combined sec-
tion of the three cerebellar peduncles (the limits
of each are not marked) ; c.q.s. , c.q.i., corpora
quadrigemina (superior and inferior) ; fr, frsenu-
lum veil ; /, fibres of the fillet, seen on the sur-
face of the tegmentum ; c, crusta ; l.g., lateral
groove ; c.g.i., corpus geniculatum internum ; th,
posterior part of thalamus ; p, pineal body. The
Roman numbers indicate tho corresponding cra-
nial nerves.

into which a pointed tent-shaped pro-
jection of the roof of the ventricle extends ( fig. 59, A, in longitudinal section).
This projection is bounded below by the inferior medullary velum, which in like
manner is prolonged from the white substance of the central part of the cere-
bellum. It is less easily displayed than the superior velum, being concealed by

Fig. 40. — ANTERIOR BOUNDARY (FLOOR) OF THE FOURTH VENTRICLE. (E.A.S.)
NATURAL SIZE.

m. s., median sulcus ; str, striae acusticaa, marking the limit between the pon-
tine part of the ventricle and the medullary part or calamus scriptorius; l.r., lateral
recess ; i.f., inferior (posterior) fovea ; a.c., ala cinerea ; t.a., trigonum acustici ;
s.f., superior (anterior) fovea, close to the lateral margin of the superior part of
the ventricle.

ta a part of the cerebellum, which is attached to its under or
posterior surface. It will be further noticed in the description of
the cerebellum. BeloAV the inferior velum the roof is formed
by a simple layer of flattened epithelium covered by pia mater ;
but it is not quite complete, for there is a hole in it termed
the foramen of Majendie a little above the place where the central canal opens
out into the ventricle, and there are tA\ro other apertures in the epithelial roof
in the lateral recesses just mentioned. At the sides and beloAV, this layer
of epithelium passes into continuity with the epithelium covering the floor,

THE FOURTH VENTRICLE.

49

but it is somewhat thickened by the addition of white nervous matter before
reaching the lateral boundaries of the floor. This thickening is left as a slightly
prominent and often ragged membrane when the epithelium of the roof of the

C

i

Fig. 41. — DIAGRAMS TO SHOW THE SITUATION OF THE CHIEF NERVE-NUCLEI IN THE MEDULLA OBLONGATA

AND PONS NEAR THE FLOOR OF THE 4lH VENTRICLE. TWICE THE NATURAL SIZE.

A, from behind ; B, profile view of the right half, the medulla and pons being supposed to be trans-
parent. The efferent or motor nuclei are shaded with oblique lines, the afferent or sensory nuclei with
dots. In A the efferent or motor nuclei are represented on the, right side only, the afferent or sensory
on the left. ///, IV, oculomotor and trochlear nucleus; V.d, descending root of the fifth
nerve ; V. s, so-called sensory nucleus of the fifth ; V.a, ascending root of the fifth ; V.m, motor
nucleus of fifth nerve ; VI, nucleus of abducens ; VII, nucleus of facial ; n. VII, root of facial curving
round abducens nucleus ; VIII, inner or dorsal nucleus of auditory ; VIII1, outer or ventral nucleus of
auditory ; IX, X. vago-glossopharyngeal nucleus ; n.a., nucleus ambiguus, accessory or efferent vago-
glosso-pharyngeal nucleus ; XI, nucleus of spinal accessory ; XII, nucleus of hypoglossal ; XII',
issuing roots of hypoglossal.

ventricle is torn off with the pia mater. It commences at the apex of the clava,
and accompanies the lateral boundary for a short distance ; then turns over the
surface of the restiform body and terminates close to the place whence the roots
of the vagus and glosso-pharyngeal nerves issue. It is termed the tc&nia or ligula-
(fig. 44, t), and its upper transverse part forms the lower boundary of the lateral

VOL. III. K

50 THE MEDULLA OBLONGATA AND PONS VAROLII.

recess of the ventricle. Another thickening of the roof is seen at the apex of the
ventricle covering the point of the calamus scriptorius : this is named the olex.

Two longitudinal vascular inflexions of the pia mater, known as the choroid
plexuses of the 4th ventricle, project from the roof into the cavity, one on either side
of the middle line, covered everywhere, however, by the epithelium of the roof.
Offsets from these pass also into the lateral recesses, from the apices of which they
emerge, encircled by a duplicate of the ligula, which was termed by Bochdalek the
cornucopia. The epithelial layer of the roof of the ventricle follows all the convolu-
tions of the choroid plexuses, but is nowhere pierced by them ; it is generally
described as the epithelium of the plexuses.

The floor or ventral boundary of the 4th ventricle is marked at its widest
part, i.e., at the level of the lateral recesses, by seme transverse white lines, which
cross the grey matter of the floor, and are known as the strice medullares seu
acusticw (figs. 39, 40, 41, sir).

These strife are caused by bundles of white fibres which emerge from the raphe, within
which they can be traced to the ventral surface of the bulb, and curve outwards over the
restiform body, where they are usually described as passing into the lateral root of the
auditory nerve. It is certain, however, that this is not the destination of most of the fibres
of the medullary strife, which are distinctly to be traced to the flocculus of the cerebellum
(fig. 49, p. 59). They vary greatly in development even upon the two sides of the same brain
(compare especially Bechterew, Neurol. Centralbl., No. 10, 1892).

One bundle of these strife is sometimes seen, usually on one side only, taking a course
obliquely upwards and outwards, passing at the lateral boundary of the ventricle into the
middle cerebellar peduncle (aberrant 'bundle of stride medullares, Klangstab of Bergmann).

The floor of the ventricle is bisected by a slight median groove. A little on
either side of this groove and immediately below the striae medullares, is a small
triangular depression (inferior fovea, fig. 40, «'./.), the apex of which extends only as
far as the striae, but the base is prolonged into two grooves extending one from
each angle. The inner of the two grooves passes with a slightly curved course
towards the point of the calamus scriptorius, and thus cuts off a pointed triangular
area, which is bounded mesially by the median sulcus, and the base of which is
turned towards the striae acusticse. This area (irigonum hypoglossi) is slightly
prominent, and constitutes the lower end of the fasciculus teres ; in it is the
prolongation of the tract of nerve-cells from which the roots of the hypoglossal
nerve take origin. The outer of the two grooves passes downwards with a slight
outward obliquity nearly to the lateral boundary of the ventricle, and marks off
externally another triangular area (irigonum acustici, La.), the base of which is also
directed upwards, where it can be traced into a prominence (best marked in children)
over which the striae acusticse course. To this prominence the name tuberculum
laterale seu acusticum has been applied, since the main part of the auditory nerve
arises in connection with it and with the triangular lateral area below it.

Included between the two grooves is a third triangular area (irifjonum vagi), the
apex of which is at the inferior fovea, while its base looks downwards and outwards.
This area has a distinctly darker colour than the rest of the floor of the ventricle,
and especially than the trigonum hypoglossi on the inner side, which has a whitish
grey appearance, and it has accordingly been named the ala cinerea (a.c). Towards
the apex it is somewhat depressed, but below it is elevated into a distinct prominence
(eminentia cinerea). It contains the nucleus of the vagus, and superiorly, near the
inferior fovea, of the glosso-pharyngeal nerve.

Above the strias acusticae the floor of the fourth ventricle is marked in
the middle of each lateral half by a distinct somewhat angular depression in a line
with the inferior fovea, from which it is separated by the eminence over which the
strias acusticae pass. This depression is termed the superior fovea (s.f.}. Between
it and the median sulcus is the prolongation of the funiculus teres, which is pro-

STRUCTURE OF THE MEDULLA OBLONGATA.

51

minent (eminentia teres} opposite the fovea but becomes gradually less so above and
below. Extending from the superior fovea to the upper end of the ventricle, where
this narrows to the Sylvian aqueduct, is a shallow depression (locus cmruleus) distin-
guished in the adult by its dark grey or slaty tint, which is due to a subjacent tract of
pigmented nerve-cells (substantia ferruginea). The trophic fibres in the fifth nerve
have been supposed to be derived from these cells.

INTERNAL STRUCTURE OF THE MEDULLA OBLONGATA.

The internal structure of the medulla, like the external form, will be best under-
stood by tracing its several parts upwards from the spinal cord ; and this can be

Fig. 42. — SECTION OF THE MEDULLA OBLONGATA AT THE MIDDLE OF
THE DECUSSATION OF THE PYRAMIDS (Lockhart Clarke).

•/, anterior ; f.p., posterior fissure ; a p., pyramid ; a, remains
of part of anterior cornu, separated by the crossing bundles from
the rest of the grey matter ; I, continuation of lateral column of
cord ; R, continuation of substantia gelatinosa of Rolando ; pc. ,
continuation of posterior cornu of grey matter ; f.g., funiculus
gracilis.

most readily done by a comparison of the appear-
ances of successive transverse sections.

Lower or closed part of the medulla oblcm-
gata. — The first changes are produced, in its internal
structure as in its external form, by the passage of the
fibre-bundles of the lateral pyramidal tract obliquely

through the grey matter of the anterior horn, and across the anterior median fissure
toihe pyramid of the opposite side (fig. 42). By this abrupt passage of a large
number of white fibres through it, the anterior horn is broken up, and one part, the
caput cornu (a), is entirely separated from the rest of the grey matter; whilst only

Fig. 43. — SECTION OF THE MEDULLA OBLONGATA

IN THE REGION OF THE SUPERIOR PYRAMIDAL

DECUSSATION. (Schwalbe. ) \

a.m./, anterior median fissure ; f.a., superficial
arciform fibres emerging from the fissure ; py, pyra-
mid ; n.ar., nucleus of the arciform fibres ; f.a'.,
deep arciform fibres becoming superficial ; o., lower
end of olivary nucleus ; o', accessory olivary nucleus ;
n.l., nucleus lateralis ; f.r.', formatio reticularis ;
f.a.2, arciform fibres proceeding from formatio reti-
cularis ; y, substantia gelatinosa of Rolando ; a. V.,
ascending root of fifth nerve ; n.c. , nucleus cuneafcus :
rt.c'., external cuneate nucleus ;/.c., funiculus cune-
atus ; n.g., nucleus gracilis ; /.</., funiculus gracilis ;
p.m./., posterior median fissure; c.c., central canal
surrounded by grey matter, in which are, n.XI.
nucleus of the spinal accessory, and, n.XIL, nucleus
of the hypoglossal ; s. d. , decussation of fillet or su-
perior pyramidal decussation.

the base of the horn remains, as a small
portion of grey matter close to the antero-
lateral aspect of the central canal.

The separated portion of the anterior

horn becomes pushed over to the side by the development of the pyramid and the
interpolation higher up of the olivary body between them, so that it comes to lie
close to the separated caput cornu posterioris (see below). The greater part of
the grey substance is broken up into a formatio reticularis (fig. 43,/.r.), i.e. a compara-

E 2

52 THE MEDULLA OBLONGATA AND PONS VAROLII.

tively coarse network of grey matter containing nerve-cells, intersected by bundles of
white fibres ; but a small part, probably representing the lateral horn of the cord, and
like that containing numerous nerve-cells many of relatively large size, remains for a
time in the lateral column, near the surface, and is known as the nucleus lateralis
(fig. 43, ».?.)•

Meanwhile the posterior horns have become gradually shifted laterally, simulta-
neously with an increase in size of the posterior columns of the medulla, so that in
place of forming an acute angle with the posterior median fissure, they now lie
almost at right angles to it (fig. 42). Moreover, the caput cornu enlarges and

&.R.

Fig. 44. — TRANSVERSE SECTION OF THE MEDULLA OBLONGATA SOMEWHAT ABOVE THE MIDDLE OF THE
OLIVARY BODY. (E.A.S.) MAGNIFIED 5 DIAMETERS. ( From a photograph. )

p.l. b, posterior longitudinal bundle ; n.t, nucleus of funiculus teres ; n.XII, nucleus hypoglossi ;
n.X, nucleus vagi ; n'X, nucleus ambiguus ; s, fasciculus solitarius ; n.p, nucleus posterior (cuneatus) ;
f.r, formatio reticularis ; t, tsenia ; s.R, substantia Rolandi ; a. V, ascending root of fifth ; c.r, corpus
restiforme ; ar.int, internal arcuate fibres ; X, issuing root of vagus ; n.l, nucleus lateralis ; n', groups
of large cells, perhaps belonging to nucleus lateralis; a-l.tr, antero-lateral ascending tract; n.d.o,
nucleus dentatus olivse ; acc.o, accessory olivary nucleus; s. o, siliqua olivse ; k.o, hilum olivse ; p,
pyramid ; /, fillet ; r, raphe ; n.ar, nucleus of arcuate fibres ; ar.ext, external arcuate fibres.

comes close to the surface, where it presently forms a distinct projection, the funiculus
of Rolando, which, a little higher up, swells into the tubercle of Rolando (fig. 42, .R.).
At the same time the cervix cornu diminishes in size and like the anterior cornu is
eventually broken up by the passage of transverse and longitudinal bundles of white
fibres through it, into a reticular formation, which then separates the caput cornu
posterioris (fig. 43, #.) from the rest of the grey matter, and joins the reticular for-
mation derived from the rest of the grey matter. In the tubercle of Rolando the
caput cornu is close to the surface, and its grey substance can readily be seen, but
above the tubercle it lies deeper, being covered by a well-marked bundle of white
fibres, the so-called ascending root of the fifth nerve (a. V.\ and by the oblique
arched fibres which are passing over it to form the restiform body.

The fibres of the ascending trigeminal root have been supposed to take origin from the cells
of the tubercle of Rolando, but this is not the case, for firstly they do not grow from these

UPPER PART OF THE MEDULLA OBLONG ATA.

53

cells, but from the cells of the Gasserian ganglion (His), and secondly, if the sensory root of
the fifth is cut at its exit from the pons, the fibres of the so-called ascending root degenerate,
but the cells of the adjacent gelatinous substance remain unaffected (Bechterew). There may,
however, be a physiological connection established with these cells by means of collateral
fibres, as in the case of the fibres of the posterior columns of the cord and the substance of
Rolando of the posterior horn.

The grey matter of the base of the posterior horn undergoes a considerable in-
crease as we trace it upwards in sections. Portions of grey matter are soon found
to extend from it into the funiculi graciles and cuneati, forming the so-called nuclei
of those columns (fig. 43, n.g., n.c.). These nuclei are at first narrow in trans-
verse section ; but as the central canal approaches the posterior surface of the
medulla they appear as comparatively thick masses, which produce externally the

Fig. 45. — SECTION ACROSS THE MEDULLA OBLONGATA A

LITTLE BELOW THE POINT OF THE CALAMUS SCRIP- ,,

TORIUS (Lockhart Clarke).

c, central canal; /, anterior median fissure ; /.</.,
funiculus gracilis; f.c., funiculus cuneatus; t.R., tuber-
cle of Eolando ; o, olivary body ; a.p., pyramid ; XI,
XII, spinal accessory and hypoglossal nerves ; XI'. XII',
their nuclei.

eminences of the clava and the cuneate
tubercle. Outside the nucleus of the funi-
culus cuneatus an accessory or external nu-
cleus becomes formed (fig. 43, n.c.). From
this nucleus fibres pass directly into the resti-
form body. The nerve-cells of the gracile
nucleus are for the most part larger than

those of the cuneate nucleus, but those of the accessory cuneate are larger than
either (50/i to 80/x). The accessory cuneate nucleus is supposed to represent a
continuation of Clarke's column of the cord (Blumenau), while in the grey matter
of the nucleus gracilis and principal nucleus cuneatus most of the ascending fibres
of the posterior column of the cervical cord become lost.

From the lower parts of these nuclei fibres are seen to emerge and to sweep forwards
and inwards in a curved manner (internal arched or arcuate fibres) towards the raphe
or septum which unites the two halves of the medulla oblongata. Having here
intercrossed with those from the opposite side in a decussation which lies above
that formed by the fibres of the pyramids (decussation of the fillet), they form
a considerable bundle of longitudinally coursing fibres which lies just dorsal to the
pyramid and is known as the fillet (lemniscus) . Its fibres receive their myelin
much earlier than those of the pyramid. On section of the fillet higher up some of
its fibres degenerate downwards and the degeneration also affects internal arched
fibres connecting them with the opposite nuclei. These therefore have their origin
from cells higher up in the brain.

Upper or ventricular part of the medulla oblongata. — When the slit-like
upper end of the central canal opens out into the fourth ventricle, the small remaining
portion of the base of the anterior horn, which in the closed part was ventro-lateral
to the central canal, comes to the surface at the floor of the ventricle, and as the
sections are traced upward increases gradually in size, producing the prominence of
the funiculus teres. In it, both in the lower part of the bulb where the canal is
still closed and above where it has opened out, a group of large nerve-cells (n.XII.)
is seen in all transverse sections. From this group (column) of cells the successive
bundles of the roots of the hypoglossal or twelfth cranial nerve arise and pass obliquely
through the substance of the bulb to leave it on its anterior aspect. The tract of
nerve-cells is accordingly known as the hypoglossal nucleus.

54 THE MEDULLA OBLONGATA AND PONS VAROLII.

At the fourth ventricle the hypoglossal nucleus lies a short distance from the surface
covered by a flattened bundle of longitudinally running white fibres, which gives this
mesial triangle of the calamus scriptorius (trigonum hypoglossi) a white appearance.

nX't

C.r.

•ruam.

Fig. 46. — SECTION OF THE MEDULLA OBLONGATA

AT ABOUT THE MIDDLE OF THE OLIVARY

BODY. (Schwalbe. ) f

f.l.a., anterior median fissure ;^ n.ar., nu-
cleus arciformis; p., pyramid; XII., bundle
of hypoglossal nerve emerging from the surface ;
at b, it is seen coursing between the pyramid and
the olivary nucleus, o. ; f.a.e., external arciform
fibres; n.l. , nucleus lateralis ; a., arciform fibres
passing towards restiform body partly through
the substantia gelatinosa, (>., partly superficial to
the ascending root of the 5th nerve, a. V. ; X. ,
bundle of vagus root, emerging ; f.r., formatio
reticularis ; c.r., corpus restiforme, beginning
to be formed, chiefly by arciform fibres, superfi-
cial and deep; n.c., nucleus cuneatus ; n.g.,
nucleus gracilis ; t, attachment of the ligula ;
f.s., funiculus solitarius ; n.X., n.X'., two
parts of the vagus nucleus ; n.XIL, hypoglossal
nucleus; n.t., nucleus of the funiculus teres;
n.am., nucleus ambiguus ; r., raphe ; A., con-
tinuation of anterior column of cord ; o', o ,
accessory olivary nuclei ; p.o.L, pedunculus olivse.

Nearer to the surface of the floor and nearer also to the median groove is a small
group of cells, known sometimes as the nucleus of the funiculus teres (fig. 46,
n.t.). The cells are small and appear to give origin to fibres which belong to the
vago-glossopharyngeal roots.

Vili

Fig. 47. — TRANSVERSE SECTION OF THE UPPER PART OF THE MEDULLA OBLONGATA. (Schwalbe.)

py., pyramid ; o., olivary nucleus ; V.a., ascending root of the fifth nerve ; V11I., root of the
auditory nerve, formed of two parts, a. and b., which enclose the restiform body, c.r. ; n, VIII. p.,
principal (dorsal) nucleus of the auditory nerve; n.VIII.ac.. accessory nucleus; g, ganglion cells
in the root ; n.f.t., nucleus of the funiculus teres ; n.XIL, nucleus of the hypoglossal; r., raphe.

At the base of the posterior horn in the lower part of the bulb, and near the
centra canal, a group of cells (fig. 43, n. XI.} is seen in section, which if traced up-
wards is found to be pushed to the side as the central canal opens, so that in the

NUCLEUS OF THE OLIVARY BODY. 55

floor of the ventricle it lies lateral or dorso-lateral to the hypoglossal nucleus. These
cells form the upper or bulbar part of the nucleus of the spinal accessory.1
Above the level where the roots of this nerve cease to come off a mass of grey matter
with numerous cells is seen lying lateral to the hypoglossal nucleus in a situation
near the floor of the ventricle corresponding to the prominence of the ala cinerea
(trigonum vagi) which appears on the surface, and it extends upwards as far as the
fovea inferior. In connection with it there arise successively bundles of fibres of the
roots of the vagus and glosso-pharyngeal nerves (lUth and 9th cranial nerves) :
those of the vagus beginning at the commencement of the ventricle, and arising
along the length of the ala cinerea ; and those of the glosso-pharyngeal coming for
the most part from the upper part of the ala cinerea, and from beneath the inferior
fovea. The grey matter in question forms then the principal nucleus of the
pneumogastric and glosso-pharyngeal nerves.

It has been inferred from the clinical and pathological evidence met with in cases of
bulbar paralysis that the motor fibres to the palate and vocal cords, which leave the medulla
oblongata by the spinal accessory roots, have their real origin in the hypoglossal nucleus. On
the other hand \jh.e pars intermedia of the seventh nerce is said to arise from the upper end of
the glossopharyngeal nucleus (Duval.)

Close to this nucleus, but placed somewhat more deeply in the grey matter, is a
round longitudinal bundle of white fibres termed ihefuniculus solitarius (figs. 44, s.,
46, /«.). This bundle, which is surrounded by gelatinous grey matter with many
small nerve-cells, occupies the same relation to the ninth and tenth nerves that the
so-called ascending root of the fifth occupies to the trigeminal. Its fibres appear to
lose themselves amongst the cells of the enclosing grey matter, and this and the
bundle gradually disappear when traced towards the spinal cord : traced upwards
they pass out with the bundles of nerve-roots which go to form the vagus and glosso-
pharyngeal, especially the latter. Both this bundle and those forming the ascending
root of the fifth have their niyelin sheath developed at an early period. As His has
shown, they grow into the medulla oblongata from the ganglia of the vagus and
glosso-pharyngeal, in the same way as the posterior roots grow into the medulla
spinalis from the spinal ganglia.

Lying in the reticular formation and ventral to the principal mass of grey matter
which here occupies the floor of the fourth ventricle, is a small detached pear-shaped
mass of grey matter containing nerve-cells, which is connected by a kind of stalk
with the rest of the grey matter. This nucleus, which was formerly termed the
nucleus ambiguus, gives origin to fibres which pass along the stalk obliquely towards
the floor of the fourth ventricle and then turn outwards and forwards to issue with
the root-bundles of the 'tenth nerve from the side of the bulb. It is therefore an
accessory vagal nucleus and, in its relation to the grey matter and in the size
and character of its cells it is a counterpart of the nucleus of the seventh nerve,
which appears in sections somewhat higher up (in the pons). A prolongation of this
nucleus gives origin higher up to fibres of the glossopharyngeal.

The issuing bundles of the auditory nerve pass partly dorso-lateral and partly
ventro-mesial to the restiform body. The dorsal division contains a large number of
nerve-cells (ganglion radicis cochlearis), which probably give origin to many of
its fibres. Ventral to the restiform body and between the two roots is another mass of
ganglion-cells, which has been termed the accessory auditory nucleus (Schwalbe)
(fig. 47, n. VHI.ac}. From these cells fibres are seen both in the upper part of the bulb
and in the pons passing transversely towards the opposite side ; they belong to the

1 The bulbar or accessory part of the nerve : the spinal part of the nerve takes origin in the ventro-
lateral group of cells of the anterior horn of the spinal cord (cervical region).

56 THE MEDULLA OBLONGATA AND PONS VAROLII.

system of the trapezium (p. 47). Higher up this nucleus blends with the ganglion
of the lateral root, the two together forming a ventral nucleus for the auditory
nerve (fig. 49, VIII.v.}.

Towards the upper part of the bulb an extensive tract of grey matter containing
small scattered nerve-cells becomes developed outside the vago-glossopharyngeal
nucleus. This tract corresponds to the lateral triangular area (trigonum acustici)
which is seen on the surface outside the ala cinerea. Into it most of the fibres
of the ventral or vestibular division of tbe auditory nerve apparently pass ; it is
termed the inner or dorsal auditory nucleus (fig. 47, n.VIIl.p). Ventral
to this nucleus is a collection of grey matter with large nerve-cells, the nucleus of
Deiters. Its cells appear to be connected with the cerebellum, for it becomes
atrophied after removal of the cerebellar hemisphere of the same side in the new-
born animal.1 Associated with this group of cells is a longitudinal bundle of nerve-
fibres which has been termed by Roller the ascending root of the auditory nerve
(fig. 49, /?.), but the precise connection of these fibres with the roots of the eighth
nerve has yet to be established. Most of these collections of cells will be again
noticed in dealing with the structure of the pons.

The nerve-cells in the hypoglossal nucleus are largest ; those in the principal
nucleus of the spinal accessory of moderate size, and those in the vago-glossopharyn-
geal nucleus are small and fusiform : those of the principal (dorsal) auditory nucleus
are the smallest. There are a number of small cells in the ventral part of the hypo-
glossal nucleus (small-celled hypoglossal nucleus of Roller), but they do not give
origin to any of the fibres of the nerve (Forel).

Nucleus of the olivary body. — Besides those collections of grey matter which
are traceable from the grey matter of the spinal cord, portions occur in certain parts
of the medulla oblongata, which are not represented in the cord. Of these the most
striking is the nucleus of the olivary ~body, which has been termed, from its appear-
ance in section, the corpus dentatum of the olive (fig. 44). It is enclosed in the
olivary prominence, and is therefore situated in the lateral area of the bulb, but
the grey matter is not visible from the surface, being covered by both longitudinal
and transverse white fibres. It takes the form of a thin wavy lamina, which is
curved round at its edge so as to form an ovoid scalloped capsule. The open part or
hilum of this looks towards the middle line and receives a considerable tract of white
fibres, which emanate from the raphe, being derived to all appearance from the
opposite olive, and pass into the hilum along its whole extent, forming the so-
called olivary peduncle (p.o.).2 Under the microscope the nucleus appears as a wavy
band of neuroglia, with small multipolar nerve-cells embedded in it. The fibres of
the olivary peduncle diverge as they pass to the grey lamina. They are partly lost
in the grey matter of the olivary nucleus but mostly pass in small bundles through
the lamina, those which are more posterior turning backwards and coursing obliquely
through the posterior part of the lateral area to join the restiform body and thus to
pass to the cerebellum as internal arched fibres. These internal arched fibres are
easily distinguishable by their small diameter from the large internal arched fibres
which belong to the tract of the fillet : moreover they develope their myelin sheath
later. Others after coursing through the grey lamina and running between the longi-
tudinal fibres which cover the olive reach the surface, where they bend round and are
continued as part of the layer of external arched fibres into the restiform body.
Through the restiform body, the arched fibres and the fibres of the olivary peduncles,
the cerebellar hemisphere of one side is connected therefore with the olivary nuclei

1 The nucleus of Deiters was formerly regarded as giving origin to part of the auditory nerve, and
is also known as the outer or superior auditory nucleus (see p. 62).

2 Some fibres emerge from the hilum and turn sharply round the ventral and lateral borders of the
dentate nucleus, to which they form a kind of capsule (fig. 44, s.o. ).

NUCLEUS OF THE OLIVARY BODY.

57

of both sides. But the connection with the opposite side is the more intimate, for
it is found that in cases of atrophy of the cerebellar hemisphere of one side, the olive
of the opposite side is atrophied, while that of the same side is intact. And it was
found by Gudden that after removal in the new-born animal of the one cerebellar
hemisphere, the opposite olive was atrophied. On the other hand the olivary
nucleus appears to be connected with the cerebral hemisphere of the same side by
a tract of longitudinal fibres which lies lateral and dorsal to the nucleus in the
medulla oblongata, and passes up towards the brain in the reticular formation. Thus

20

r.g. -\ ^W XII rM

Fig. 48. — PART OF THE KETICDLAR FORMATION OF THE MEDULLA OBLONGATA (Henle).

r.a., reticularis alba : r.g., reticularis grisea ; between them a root-bundle of the hypoglossus (XII),
The longitudinal fibres of the reticular formation are cut across ; the transversely coursing fibres are
internal arcuate fibres, passing on the right of the figure towards the raphe.

the olives are intermediary stations between the cerebrum and cerebellum : they have
no direct connection with the cord (Flechsig).

Besides the main olivary nucleus two smaller isolated bands are generally seen
(figs. 43, 44, 46), looking like separated portions of the chief nucleus. They
are situated one on the dorsal, and the other on the mesial aspect of the chief
nucleus, and are known as the outer and inner accessory olivary nuclei. They
are traversed like the main nucleus by bundles of internal arched fibres going to
the restiform body, and are frequently connected at one or two places to the main
nucleus. The inner accessory nuclei are sometimes termed the pyramidal nuclei,
for they lie immediately behind the pyramids. The root-bundles of the hypoglossal
nerves generally pass between them and the chief olivary nucleus after traversing
the olivary peduncle, but sometimes the nerve pierces the chief nucleus near its mesial
edge.

Other small collections of grey matter and nerve-cells are scattered in certain
parts of the formatio reticularis, as well as one or two distinct tracts in connection

58 THE MEDULLA OBLONG ATA AND PONS VAEOLII.

with the external arched fibres, and a considerable amount in the median septum or
raphe. These three structures may therefore next be described.

The formatio reticularis (figs. 43, 44, 46, f.r.) occupies thewhole of the anterior
and lateral areas of the bulb, dorsal to the pyramids and olives respectively. It is
thus named on account of the appearance which it presents in a transverse section
viewed under a moderate magnifying power. This reticular appearance is
caused by the intersection of bundles of fibres belonging to two sets which run at
right angles to one another. Those of the one set are longitudinal, and these are
intersected by transverse fibres, which pass obliquely from the raphe outwards and
somewhat backwards with a curved course towards the funiculus gracilis and f uniculus
cuneatus, and the olivary nucleus ; and also in the upper part of the medulla oblongata
towards the restiform body.

In some parts grey matter with nerve-cells enters into the constitution of the
formatio reticularis. The cells are especially large and numerous in the reticular
formation of the lateral area near the anterior area, where in the lower part of
the medulla oblongata is situated a remnant of the anterior horn ; and its grey
matter is presumably derived in great measure from the latter. In the anterior or
mesial area of the bulb, nerve-cells are mostly absent from the formatio reticularis,
and this is therefore sometimes distinguished as the formatio reticularis alba (fig. 48,
r.a.), from the other or formatio reticularis grisea (r.g.).

The longitudinal fibres of the reticular formation of the anterior area comprise
at least two sets, viz. : — (1) those which occupy the tract nearest to the pyramids and
which belong to the tract of the fillet above described ; and (2) those which are pro-
longed from the remainder of the anterior column of the spinal cord after the passage
of the anterior (direct) pyramidal tract into the outer side of the pyramid. The
latter become in the higher levels of the medulla oblongata gradually obscured or
replaced by an accumulation of grey matter which resembles that of the grey reticular
formation and has been -termed by Roller, nucleus centralis. But some of the
longitudinal fibres of the anterior area remain distinct, and become in the upper
regions of the medulla oblongata collected into a compact bundle which is known
as the posterior or dorsal longitudinal bundle.

The fibres of the reticular formation of the lateral area are prolonged from the
remains of the lateral column after the lateral pyramidal tract and the dorsolateral
cerebellar tracts have passed to their respective destinations. Those which are
nearest the olivary nucleus mostly belong to the anterolateral cerebellar tract (fig. 44).
The fibres of the lateral area are added to as we trace them upwards in sections, the
increase being due either to the turning upwards of some of the inner arched fibres
or to the accession of fibres which are derived from nerve-cells in the grey matter
near the posterior surface, or in the grey reticular formation.

According to Deiters, the nerve-fibre processes of the nerve-cells of the reticular
formation all pass downwards, while their branched processes are directed
horizontally.

The arched or arcuate fibres of the medulla oblongata, which have been more
than once alluded to, are the curved fibres which are seen in transverse sections
coursing in the plane of the section. From their position they are distinguished into
external and internal, or superficial and deep.

The outer or superficial arched fibres (figs. 44, 46) emerge for the most part
from the anterior median fissure, and passing over the pyramids and olives, many
of them go to the restiform body. They are added to by deep fibres which come to
the surface partly in the groove between the pyramids and olives, partly after passing
through the olives, as before mentioned. Traced back in the anterior median fissure
they are seen to enter the raphe, and to cross over in it ; after which it is supposed
that they may become longitudinal, but their further course is not certainly known.

INTERNAL STRUCTURE OF THE PONS VAROLII.

59

The inner or deep arched fibres emerge from the raphe, and traverse the thickness
of the bulb, tending towards the olives, the restiform body, and the nuclei of the
cuneate and slender f uniculi. Those which pass through and in front of the olives
are in continuity with the superficial arched fibres.

Traced backwards into the raphe, the deep arched fibres cross obliquely to the
other side of the medulla, where some become longitudinal, joining the fibres of the
fillet. Others are the fine fibres before alluded to as connecting the cerebellar
hemisphere with the opposite olive.

Fig. 49. — TRANSVERSE SECTION OP PONS VAROLII THROUGH THE ORIGIN OF THE AUDITORY NEKVE.
(E.A.S.) (From a photograph. ) Magnified about 4 diameters. /

v.IV. , 4th ventricle ; c., white matter of cerebellar hemisphere ; c.d., corpus dentatum cerebelli ;
/. , flocculus ; c. r. , corpus restiforme ; E, Holler's ascending auditory bundle ; I), Deiter's nucleus ;
VIII, issuing root of auditory nerve ; VIII. d., dorsal nucleus ; VIII.v., ventral (accessory) nucleus
of auditory; n.tr., small-celled nucleus traversed by fibres of the trapezium; tr., trapezium;/.,
fillet ; p.l.b., posterior longitudinal bundle ; f.r., formatio reticulario ; n, n', n", nuclei in formatio
reticularis ; V.a., ascending root of 5th; s.ff., substantia gelatinosa ; s.o., upper olive; VII, issuing
root of facial ; n. VII., nucleus of facial ; VI, root bundles of abducens ; py., pyramid bundles ; n.p. ,
nuclei pontis.

Nuclei of the superficial arched fibres. — Amongst the superficial arched
fibres, or between them and the subjacent columns of the bulb, small collections
of grey matter with nerve-cells are here and there met with, which are distinguished
by the above name. The principal group of cells lies superficial to the pyramid on
either side (figs. 44, 46, n.ar.). This group becomes very largely developed at the
junction of the medulla oblongata with the pons Varolii.

The raphe or septum (fig. 44, r) is composed of fibres which run in part dorso-
ventrally (fibras rectse), in part longitudinally, and in part across the septum more
or less obliquely. Intermixed with the nerve-fibres are a number of nerve-cells in
grey matter. The fibrse rectae are continuous ventrally with the superficial arched
fibres, which emerge at the anterior median fissure ; dorsally in the upper part of the
bulb with fibres from the medullary strise (cf. p. 50). The longitudinal are chiefly

60 THE MEDULLA OBLONG ATA AND PONS VAROLII.

fibres which have passed into the raphe as floras rectae or as superficial or deep arched
fibres, and in it have altered their direction and become longitudinal. The obliquely
crossing fibres are the deep arched fibres which enter or emerge from the raphe.
Others, however, seem to come from the nuclei of the nerve-roots, and these may
pass more directly across as commissural fibres either into the reticular formation or
into the pyramid of the other side, in either case becoming longitudinal. The nerve-
cells of the raphe are multipolar cells, those in the middle being chiefly spindle-
shaped. The latter are connected with fibrse rectas (Clarke), whilst the more laterally
situated ones, at least those near the anterior median fissure, are connected with
some of the superficial arched fibres.

Internal structure of the pons Varolii. — Sections of the pons are greatly
modified by the appearance of the transversely coursing fibres between the two halves
of the cerebellum which have already been noticed. These occupy the whole of the
ventral portion and enclose and conceal from view the bundles of the pyramids, which
can be traced upwards into and through the pons from the medulla oblongata.

Between the bundles of fibres of this ventral portion of the pons grey matter
with small multipolar nerve-cells is everywhere found (nuclei pontis (fig. 49, n.p.}).
It is probable that many of the transverse fibres terminate in this grey matter and
are through it connected in some way with the longitudinal fibres of the pyramidal
tract ascending through the pons ; but the transverse fibres do not appear to turn
upwards, for they are smaller than the longitudinal fibres.

The posterior or dorsal portion of the pons is chiefly constituted by a continua-
tion upwards of the reticular formation and of the grey matter of the medulla
oblongata. As in the latter, there exists here also a median septum or raphe, which
is similar in structure to that of the medulla oblongata. It does not extend through
the ventral half, being obliterated, or nearly so, by the great development of the
obliquely and transversely passing fibres, except near the upper and lower borders
where the superficial transverse fibres of the pons turn in at the middle line ; and
especially at the upper border where bundles of the same fibres encircle the crura
cerebri as they emerge from the pons.

In the reticular formation, in addition to the scattered and reticulaiiy arranged
grey matter with nerve-cells everywhere met with, there are one or two more
important collections which lie embedded in this formation and from which nerve-
fibres arise. One of these is the superior olivary nucleus, another is the nucleus of
the seventh or facial nerve, and others give origin to portions of the fifth nerve.

The superior olivary nucleus (fig. 50, o.s.) is a collection of small nerve-cells
which lies dorsal to the outer part of the trapezium, in what would correspond (as
indicated by the passage outwards of the roots of the sixth and seventh nerves) to a
prolongation of the lateral area of the medulla oblongata. In man it is very much
smaller than the inferior olive, to which it does not present much resemblance in
form, although in structure and in the size of its cells there is a close similarity. In
some animals, however, it is larger, and has a distinctly sinuous outline. From it,
as above mentioned (p. 47), fibres pass into the trapezium ; it may be connected
through these with the accessory auditory nucleus of the opposite side (p. 55).
Running upwards on the mesial side of the superior olive between this and the fillet
is a bundle of fibres which has been termed the central tract of the tcgmentum, but its
connections have not yet been satisfactorily ascertained.

Besides its connection with the contra-lateral accessory auditory nucleus through the corpus
trapezoides, the upper olive is connected, according to Bechterew, (1) to both the posterior
(inferior) corpora quadrigemina through the lower fillets, (2) to the cerebellum through the
restif orm body, (3) with the nucleus of the sixth nerve (and perhaps, also, with that of the third
and fourth nerves) through the posterior longitudinal bundle, and (4) with the spinal cord through
fibres passing down the anterior column.

THE PONS VAROLII.

61

The nucleus of the facial nerve (n. VII} lies in the reticular formation just
dorsal to the superior olivary nucleus, and at some depth, therefore, below the floor
of the fourth ventricle. It begins to be visible in sections immediately above the
medulla oblongata, in the form of small isolated groups of nerve-cells, from which
separate bundles of fibres proceed, and extends three or four millimeters upwards. Its
cells are of moderate size, and their axis-cylinder processes are directed inwards and
backwards towards the grey matter of the floor of the ventricle, where they collect

P"

VI

Fig. 50. — SECTION ACROSS THE LOWER, PAKT OF THE PONS (after Stilling and Schwalbe). £

Py> pyramid-bundles continued up from the medulla ; po, transverse fibres of the pons passing from
the middle crus of the cerebellum, before (po2) and behind (po') the chief pyramid bundles ; t, deeper
transverse fibres, constituting the trapezium ; the grey matter between the transverse fibres is not
represented either in this or in the following figures; r, raphe ; o.s., superior olivary nucleus; a. V,
bundles of the ascending root of the fifth nerve, enclosed by a prolongation of the grey substance of
Rolando ; VI, the sixth nerve ; n. VI. its nucleus ; VII, the facial nerve ; Vila, ascending portion of
the facial root ; n. VII, its nucleus ; VIII, superior root of the auditory nerve ; n. VIII, part of the
nucleus of Deiters ; v, section of a vein.

to form a longitudinal bundle, oval in section, which runs for a short distance
upwards in the grey matter and then turns sharply in a ventrolateral direction,
traversing the thickness of the pons to emerge on its lateral aspect (fig- 41, B.)
From facts brought forward by Mendel and supported by Tooth and Turner, the
facial nerves appear to receive some fibres through the posterior longitudinal bundles
from the oculomotor nuclei ; these fibres probably being those for the frontalis,
corrugator supercilii, and orbicularis palpebrarum. On the other hand the fibres to
the orbicularis oris may arise from the hypoglossal nucleus.

The motor nucleus of the fifth nerve (fig. 51, nV) comes to view
in higher sections through the pons, situated a little below the surface close to
the lateral margin of the fourth ventricle. It contains large pigmented multipolar
nerve-cells, the axis-cylinders of which pass out into the motor root of the trigeininal.
Fibres are also seen in the grey matter of the floor of the ventricle connecting both
this motor nucleus (and also the sensory nucleus, immediately to be described) with
the raphe, and through this probably with higher parts of the brain.

The so-called upper sensory nucleus of the fifth nerve (n. V) lies on the

THE MEDULLA OBLONGATA AND PONS VAROLII.

outer side of the motor root. The cells are small and arranged in clusters sepa-
rated by the fasciculi of origin of the sensory nerve-root. This collection of cells
is more extensive than the motor nucleus, being seen in sections higher up the
pons, and passing below into the so-called " lower sensory nucleus," which is a
continuation of the grey matter of the tubercle of Rolando, and ultimately,
therefore, of the substantia gelatinosa of the posterior horn of the spinal cord.
Passing towards this nucleus into the issuing roots of the fifth nerve is seen, as
has just been mentioned, in all sections through the middle part of the pons
a well marked tract of fine fibres which are traceable over the posterior longi-
tudinal bundle to the raphe, and ultimately pass, it is believed, upwards
towards the mid -brain. This tract is known variously as the crossed root,
the raphe-root, or the central tract of the trigeminal. Its fibres pass by and

Fig. 51. — OBLIQUE TRANSVERSE SUCTION OF THE PONS

ALONG THE LINE OP EXIT TRAVERSED BY THE FIFTH
NERVE (E.A.S.). 3

The section passes through the lower part of the
motor nucleus (nv1) from which a bundle of fibres of
the motor root, V, is seen passing ; a part of the upper
sensory nucleus (nv) is also shown in the section in
the form of a number of small isolated portions of
grey matter. Amongst these are a few bundles of
the ascending root cut across, but most of these
have already become diverted outwards to join and
assist in forming the issuing part of the main or
sensory root, V ; ar, arcuate fibres near the fourth
ventricle, which come partly from the raphe, partly
from a small longitudinal bundle of fibres (I) near
the median sulcus (m.s. ), and pass outwards to join
the root of the fifth nerve ; f.r., formatio reticularis ;
r., raphe ; «./., substantia ferruginea.

may in part be continuous with a small oval
bundle of longitudinal fibres (fig. 51, Z),
which lies in the grey matter not far from
the median sulcus, and which resembles in
appearance the ascending part of the facial
root.

The rest of the grey matter of the pons lies near the dorsal surface and appears
in the floor of the upper part of the fourth ventricle. Besides scattered nerve-cells,
others are collected at certain parts into definite groups or nuclei from which some
of the remaining cranial nerves take origin. Like the similarly placed nuclei in
the medulla oblongata, these also do not lie close to the epithelium which covers the
surface, but are separated from it by a layer of gelatinous substance (neuroglia) free
from nerve-cells, termed the ependyma of the ventricle.

The dorsal nucleus of the auditory nerve (fig. 47, n. VIII p.\ is prolonged
upwards underneath the striae acusticae into the pons (fig. 49, Vlll.d.}. It is widest
at about the junction of the medulla and pons, where it extends almost to the middle
line ; further up it rapidly narrows and becomes shifted towards the lateral boundary
of the ventricle as the nucleus of the sixth nerve makes its appearance between it
and the, median sulcus. Its cells are small, and it is much broken up by the pas-
sage through it of fine transverse nerve-fibres.

The so-called outer or superior nucleus of the auditory nerve, or the nucleus of
Deiters (Laura) (fig. 49, D ; fig. 50, n.VIH\ is characterized by the large size of its
cells, and lies immediately ventro-lateral to the dorsal nucleus, which has just been
described. It does not begin to be visible so far down as the latter, but is
continued as far upwards, rather increasing in size superiorly, whereas the dorsal

PONS VAROLII. 63

nucleus diminishes. It is much broken up by longitudinal fibres (ascending
auditory fibres of Eoller). The connection of this nucleus with the auditory nerve
is very doubtful. It undergoes no alteration when the auditory nerve is severed in
the new-born animal, whereas section of the spinal cord in the upper cervical region
of the new-born rabbit is followed by degeneration and atrophy of this nucleus
(Monakow). It becomes atrophied after removal of the cerebellar hemisphere of
the same side in the new-born animal (see also p. 55).

The ventral nucleus of the auditory nerve (see p. 55) which is represented
in the upper part of the medulla oblongata by a collection of nerve-cells lying in the
angle between the restiform body and the two portions of the root of the auditory
nerve (fig. 47, n. Vlll.ac} and by cells interpolated amongst the fibres of the cochlear
root (p. 55), is placed in the region of the pons between the restiform body and the
flocculus, and the cochlear root here issues directly from it (fig. 49). Its cells, which
are small and rounded but multipolar, are enclosed like those of a ganglion, each in
a nucleated capsule.

The nucleus of the sixth nerve (common nucleus of the sixth and seventh
of some authors) consists of a group (column) of large multipolar cells lying on
either side of the median sulcus (fig. 50, n.VI). It corresponds to the part of the
fasciculus teres which lies immediately above the medullary striee on the floor of
the fourth ventricle. It has a close relation to the root of the facial, which runs
along its mesial side (Vila), curves round it eventually, and appears to receive
some fibres from it, but it is doubtful if this is really the case (Growers). The fibres
of the nerve run in bundles obliquely ventralwards and downwards (caudalwards) to
emerge at the lower border of the pons. Between this nucleus and the median
groove, along the middle of the fourth ventricle, is an oval bundle of nerve fibres
(fig. 50), which runs longitudinally upwards for about 5 mm., and occupies
nearly the same position with regard to the nucleus of the sixth nerve that the
longitudinal fibres which cover the hypoglossal nucleus occupy with regard to the
origin of that nerve. The bundle in question is the ascending part of the root
of the seventh nerve (p. 61), and when followed upwards in sections its fibres are
seen to turn sharply outwards and ventralwards, and to become the issuing root of
the facial. From the nucleus of the abducens, nerve-fibres pass to join the pos-
terior longitudinal bundle, and in this they run upwards to the mid-brain, where as
Duval and Laborde have shown they join the issuing oculomotor roots of the oppo-
site side. This crossed connection between the third and sixth nerves explains
those cases of lesion of the pons in which paralysis of the external rectus muscle
of one side is accompanied by that of the internal rectus of the opposite eye.

Course of nerve-fibres from the spinal cord upward through the medulla
oblongata and pons. — Assuming for convenience of description the existence of
three white columns of the spinal cord on each side, the various parts of these are
continued upwards as follows : —

The posterior column is continued in the medulla oblongata as the white sub-
stance of the funiculus gracilis and funiculus cuneatus. The longitudinal fibres
appear to end by terminal arborisations in the grey matter which forms the nuclei ;
and numerous deep arched fibres enter or emerge from the same collections of grey
matter, passing through the raphe from the other side of the medulla, where they
are continuous with the longitudinal fibres dorsal to the pyramids which form the
main tract of the fillet (Edinger) (interolivary layer of Flechsig). The solitary bundle
and the " ascending " root of the fifth morphologically represent, as their mode of
development from ingrowing nerve fibres shows, parts of the postero-lateral column
of the cord.

Some fibres also pass from these nuclei, especially from the outer or large-celled
cuneate nucleus directly into the restiform body of the same side.

64 THE MEDULLA OBLONGATA AND PONS VAROLI1.

A large part of the lateral column of the cord, viz., the lateral pyramidal tract,
passes into the opposite pyramid of the bulb and proceeds in this and in the

Fig. 52. — DEGENERATIONS IN THE SPINAL CORD, MEDULLA OBLONGATA, PONS TAROLII, AND MESEN-

CEPHALON OP A MONKEY FOLLOWING HEMISECTION AT THE TWELFTH DORSAL NEKVE. (E.A.S.)

The hemisection was on the left side of the cord, and was complete. The section outlines drawn to
scale with a camera Incida. The degenerated fibres shown by black dots. Those in the section of the
lumbar cord are descending, all the rest are ascending, py, pyramidal tract ; d.a-l, descending antero-
lateral tract ; d.a.c, dorso-lateral ascending cerebellar tract; d.a'.c' (in Pons III.), degeneration of
fibres of this tract in the white matter of the cerebellar worm ; v.a.c, ventrolateral ascending cerebellar
tract; v'.a'.c' (in Pons II. and III.), degenerated fibres of this tract passing dorsally into the valve of
Vieussens (in Pons III. ) and into the white matter of the vermis (Pons II. ) ; n. III. , n. V., n. VI., n. VII.,
issuing ribres of the 3rd, 5th, 6th, and 7th nerve-roots ; v.IV., 4th ventricle.

ventral part of the pons towards the crusta (see fig. 24, p. 30). Together with the
small part of the anterior column of the cord which also enters into the constitution

PONS VAROLII. 65

of the pyramid, it there forms the pyramidal trad of the isthmus of Flechsig
(peduncular tract of Meynert). Some of the fibres of the pyramid, however, emerge
as external arcuate fibres, and joining the restiform body pass to the cerebellum.
Moreover, the pyramidal tract is larger in the pons and medulla oblongata than in
the spinal cord, for as it passes downwards it gives off numerous fibres to end by
terminal ramifications in the nerve-nuclei of the efferent cranial nerves. Collaterals
also pass off from the fibres of the pyramids, and even more numerously from the
longitudinal fibres of the posterior and lateral areas of the medulla oblongata and
pons to end by terminal ramifications in the grey matter (Kolliker). A part of the
lateral column of the cord forming the dorso-lateral cerebellar tract (see fig. 52, d.a.c.\
passes at about the middle of the medulla oblongata obliquely backwards in the
restiform body to the cerebellar worm. The venire-lateral ascending cerebellar tract
(v.a.c.) passes into the upper part of the pons and turning dorsally at about the level
of the exit of the fifth nerve curves backwards and enters the cerebellum over and
along with the superior peduncle and in the valve of Vieussens.

The rest of the lateral column runs up dorsal to the olives and contributes to
form the longitudinal fibres of the reticular formation. These are continued through
the dorsal parts of the encephalic isthmus towards the corpora quadrigemina and
optic thalamus. Some of the fibres become collected as they pass up towards the
pons into the well-marked flattened bundle of fibres (fillet) lying dorsal to the
pyramid. For the fillet is not, according to Edinger, wholly formed of the arched
fibres which emanate from the nuclei of the contra-lateral posterior columns ; it
receives an accession of fibres which have already crossed over in the spinal cord
from the posterior horn (through the anterior commissure), and have passed up the
antero-lateral column to the medulla oblongata. According to Flechsig and v.
Bechterew the fillet also contains fibres which are passing from the ventral auditory
nucleus through the trapezium to the inferior corpora quadrigemina.

The anterior column of the cord in part is continued into the pyramid of the
same side, but chiefly dips under the pyramid and forms the longitudinal fibres of
the white reticular formation in the dorsal part of the mesial area. These pass
upwards towards the isthmus cerebri. In the pons Varolii one tract of them
becomes collected into a well marked fasciculus (posterior or dorsal lonyiludinal
bundle, figs. 53, 54, p. I), and some of the others join the fillet ; their further destina-
tion will be afterwards noticed. In the region of the medulla oblongata they are
indistinguishable from one another in the adult, but in the foetus they are found to
develope at different periods and are then readily differentiated (Flechsig).

A small bundle of fibres of the anterior column of the cord was described by Solly as
passing: obliquely upwards below the olive, to join the restiform body (see fig. 30,/). This is
seldom distinct.

Transition from the pons Varolii to the mid-brain. — In sections through
the upper part of the pons (fig. 53) the fourth ventricle, which here becomes rapidly
narrowed, is roofed over by the two superior peduncles of the cerebellum which are
passing to the mesencephalon, and by the superior medullary velum and lingula,
which lies between them. The grey matter of the floor of the ventricle (central
grey matter) shows on either side near the median groove a group of nerve-cells con-
tinuous below with the nucleus of the funiculus teres, and above with the nucleus of
the aqueduct. More to the side is the mass of pigmented nerve-cells known as the
substantia ferrugiuea (fig. 53, s.f.), and still more laterally at the angle which the
roof makes with the floor, a column of large spherical scattered cells, along the
outer border of which a well marked white bundle — the descending root of the fifth
nerve (v.d.*) — runs downwards towards the middle of the pons where it issues with the
motor root. These cells and the fibres of the descending root can be traced upwards

VOL. III. F

66

THE MEDULLA OBLONG ATA AND PONS VAKOLII.

as far as the superior corpora .quadrigemina. Between the central grey matter and
the reticular formation on either side of the raphe is the now sharply defined dorsal
(posterior) longitudinal bundle (p.l.). The fibres which compose this, which receive

Fig. 53. — TRANSVERSE SECTION THROUGH THE UPPER PART OF THE PONS (Schwalbe, after Stilling).
Kather more than twice the natural size. *

p, transverse fibres of the pons ; py, py, bundles of the pyramids ; a, boundary line between the
tegmental part of the pons and its ventral part ; I', oblique fibres of the lateral fillet, passing towards the
inferior corpora quadrigemina; I, lateral; I2, mesial fillet; f.r., formatio reticularis ; p.l., posterior
longitudinal bundle ; s.c.p., superior cerebellar peduncle ; v.m.a., superior medullary velum ; I, grey
matter of the lingula ; v 4, fourth ventricle ; in the grey matter which bounds it laterally are seen,
v.d., the descending root of the fifth nerve, with its nucleus ; s.f., substantia ferruginea ; g.c., group
of cells continuous with the nucleus of the aqueduct.

their myelin sheaths very early, serve partly as a medium of communication between
the nucleus of the sixth nerve and the third and fourth nerves, and are partly pro-
longed downwards towards the spinal cord and upwards towards the optic thalamus.

Fig. 54. — SECTION ACROSS THE JUNCTION OF THE PONS

VAROLII AND MID-BRAIN AT THE PLACE OF EXIT OF THE

FOURTH NERVE (Stilling). THE IORSAL PART ONLY OF

THE SECTION IS REPRESENTED.

Aq, aqueduct of Sylvius ; IV, issuing fourth nerve ;
IF', its bundles decussating in the valve of Vieussens ;
IV", a bundle cut across in the central grey matter of the
aqueduct ; d. V, descending root of the fifth nerve ;
p.l, posterior (dorsal) longitudinal bundle; r, reticular
formation ; I, lateral fillet ; s.c.p, superior cerebellar
peduncle.

The fillet is also now more distinct from the neighbouring longitudinal bundles of
the reticular formation, and a considerable part of it, known as the lateral fillet, is
seen to be passing to the side of the pons, where its fibres as they course obliquely
towards the corpora quadrigemina overlap the superior cerebellar peduncle of the
same side. As the fillet thus passes gradually to the side it gives place to a round

1 The details of this and of several of the preceding figures are filled in under a somewhat higher
magnifying power than that used for tracing the outlines.

LITERATURE OF MEDULLA OBLONG ATA AND PONS VAROLII. 67

bundle of longitudinal fibres, which begins to be distinct in this region, and which
passes upwards to form the mesial bundle of the crusta (mesial fillet). The superior
cerebellar peduncle as the sections are traced upwards is seen gradually to shift
ventral- and mesial wards until in sections through the lower part of the mesen-
cephalon it reaches the raphe, and decussates with its fellow of the opposite side.

In sections through the upper part of the pons the fibres of the middle peduncles
which arch upwards as before mentioned, are cut obliquely, and their entrance
into the cerebellar hemisphere is no longer seen. The pyramidal bundles are more
scattered and also more numerous than in the lower part, and the grey matter
between them is increased in amount. In the highest sections this grey matter is
beginning to accumulate ventral to the lemniscus and reticular formation, and to
contain a considerable amount of pigment in its cells (commencement of substantia
nigra of mesencephalon).

LITERATURE OP MEDULLA OBLONGATA AND PONS VAROLII.1

Baginski, B., Uebcr den Urspruny und den centralen Verlauf des Nervus acusticus des
Kaninchens u. der Katze, Sitzungsber. d. Berliner Akad. , 1886 and 1889, and Virch. Archiv, 1890 ;
Zur Kenntniss des Verlaiifes der hinteren Wurzel des Acusticus, <L-c., Arcb. f. Psych., Bd. xxiii., 1891.

v. Bechterew, "W., Ueber die Lang sfaserzuge der formatio reticularis medullce oblongatce etpontis,
Neurol. Centralbl. 1885 ; Untersuchungcn iiber die Schleifenschicht, Berichte der Kgl. Sachsischen
Gresellsch. der Wissensch., Math.-Physik. Klasse, 1885 ; Ueber cine bisher unbekannte Verbindung der
grossen Oliven mit dem Grosshirn, Neurol. Centralbl., 1885 ; Ueber die innere Abtheilung des Strick-
korpers und den achten Hirn-nerven, Neurol. Centralbl., 1885 ; Ueber die Bestandtlieile des Corpus
restiforme, Archiv f. Anat. u. Phys., Anat. Abth., 1886 ; Ueber die Trigeminusivurzeln, Neurolog.
Centralbl., 1887 ; Zur Frage iiber den Ursprung des Hornerven und iiber die phyaiologische Bedeutung
des N. vestibularis, Neurolog. Centralbl. 1887 ; Le cerveau de Vhomme dans ses rapports et connexions
intimes, Archives slaves de biologie, t. iii., 1887 ; Ueber centrale Endigungen des Vagus und iiber
die Zusammensetzung des sogen. Fasciculus solitarius (Russian), Abstract in Neurolog. Centralbl.,
1888 ; Zur Frage u. d. StrioK medullares, &c., Neurol. Centralbl., 1892.

- Blumenau, L. , Ueber d. dusseren Kern des Keilstranges im verldngerten Mark, Neurol. Centralbl. ,
No. 8, 1891 ; Einige Bemerkungen ueber d. duss. Kern d. Keilstranges, Neurol. Centralbl., No. 19, 1891.

Bruce, A. , On the connections of the inferior olivary body, Proc. of the Koyal Society of Edinburgh,
1891.

Darkschewitsch, Ue. d. Ursprung u. d. centralen Verlauf d. N. access., Arch. f. Anat. u.
Phys., Anat. Abth., 1885.

Darkschewitsch, L. , u. Freud, S. , Ueber die Beziehung des Strickkorjiers zum Hinterstrang
und Hinterstrangskern nebst Bemerkungen iiber zwei Felderder Oblongata, Neurolog. Centralbl., 1886.

Dees. O., Ue. d. Ursprung u. d. centralen Verlauf d. Nervus accessorius, Allg. Zeitschr. f. Psych.,
Bd. xliii., 1887 ; Ueber die Beziehung d. N. accessorius z. d. Nn. vagusu. hypoglossus, ibid, xlix., 1888 ;
Zur Anat. u. Phys. d. Nervus vagus, Arch. f. Psych, xx., 1888, and Neurol. Centralbl., 1888.

Edingrer, L., Zur Kenntniss des Verlaufes der Hinterstrangfasern in der Medulla oblongata und
im, unteren Kleinhirnschenkel, Neurolog. Centralbl., 1885 ; Vorlesungen u. d. Baud. Centralnerven-
system, Leipzig, 1889.

Flechsigr, Paul, Ueber die Verbindung der Hinterstrdnge mit dem Gehirn, Neurolog. Centralbl. ,
1885 ; Zur Lehre vom centralen Verlauf der Sinnesnerven, Neurolog. Centralbl., No. 23, 1886.

Flechsig: u. Hdsel, Die Centralwindungen ein Centralorga.n der Hinterstrdnge, Neurol.
Centralbl., 1890.

Forel, A., Ueber d. Verhdltniss, <L-c., Ursprung des IX., X., u. XII. Hirnnci-ven, Festschr. f.
Nageli u. Kolliker, 1891.

Freud, S., Zur Kenntniss der Olivenzwischenschicht, Neurolog. Centralbl., 1885; Ueber den
Ursprung des N. acusticus, Monatsschr. f. Ohrenheilkunde, xx., 1886.

Gudden, H., Beitrag z. Kenntniss d. Wurzeln d. Trigeminusnerven, Allg. Zeitschr. f. Psych.,
Bd. xlviii., 1891.

Hess, C., Das Foramen Magendii und die Oeffnungen an den Recessus laterales des vierten
Ventrikels, Morpholog. Jahrbuch, x., 1885.

Hill, A., The grouping of the cranial nerves, Brain, vol. x., 1888.

Hollis, "W. Ainslie, Some points in the histology of the medulla oblongata, pons Varolii, and
cerebellum, Journal of Anat. and Physiol., vols. 18 and 19.

Homen, E. A., Ueber secunddre Degeneration im verldngerten Mark u. Riickenmark, Arch. f.
pathol. Anat., Bd. Ixxxviii., 1882.

Jelgrersma, GK, Ueber die Nuclei arciformes, Centralbl. f. Nervenheilk. , 1889.

Kazzander, G., S. radice dorsale del nervo ipoglosso, <tc., Anat. Anz., 1891.

Koch, P. D., Untersuchungen iiber den Ursprung und die Verbindungen des Nervus hypoglossus,
Archiv f. mikrosk. Anat., Bd. xxxi., 1887.

v. Kolliker, A., Der feinere Bau des verldngerten Markes, Anat. Anzeiger, 1891.

1 See also Literature of cerebellum and of origin of cranial nerves.

Y 2

68 LITERATURE OF MEDULLA OBLONGATA AND PONS VAROL1I.

Lowenthal, N., Degenerations secondaires ascendantes dans le bulbe rachidien, dans le pont
et I'etage superieur de I'isthme, Kevue medicale de la Suisse romande, v. , 1885.

Marchi, V. , Sopra un caso di doppio incrociamento del fasci jjiramidali, Archiv. ital. per le
malad. nervos., xxii., 1885.

Mendel, Ueber das solitdre JBundel, Arch. f. Psychiatric, xv., 1884 ; Ueber den Kernursprung
des Augenfacmlis, Deutsche medic. Wochenschr. , Jahrg. xiii., 1887.

Meyer, P., Beitrag zur Lehre der Degeneration der Schleife, Archiv f. Psychiatric, Bd. xvii.
1886 ; Ueber ein Fall von Pons-hdmorrhagie mit secundaren Degenerationen der Schleife, Arch. f.
Psych., xiii., 1882.

Ming-azzini, Or. , Intorno alia fma anatomia del nucleus arciformis, &c. , Atti della R. Accad.
medica di Roina, Anno xv., 1889 ; Intorno alle origine del n. hypoglossus, Ann. di freniatria, ii., 1891.

v. Monakow, Zur Kenntniss d. " ausseren Acusticuskerns" u. d. Corpus restiforme, Neurol.
Centralbl., 1882 ; and in Archiv f. Psych., Bd. xiv., 1883 ; Experimented Beitrage zur Kenntniss der
Pyramiden- und Schleifcn-bahn, Correspondenzblatt fiir Schweizer Aerzte, 1884 ; Neue experimental e
Beitrage zur Anatomic der Schleife, Neurol. Centralbl., 1885 ; Stria} acusticai u. untere Schleife, Arch,
f. Psych., xxii., ]890.

Pal, J., Ueber d. Verlauf der Fibrce arcuatai externce anteriores, Arbeiten a. d. Instit. f. allg. u.
xp. Pathologic, Wien, 1890.

Boiler, C., Der centrale Verlauf d. N. access., Zeitsch. f. Psych., 1881 ; Ueber die Schleife, Arch,
f. mikr. Anat., Bd. xix., Neurol. Oentralb. 1890.

Sala, L., Sull' origine del nervo acustico, Monitore zoologico italiano, 1891 (French in Archives
ital. de biol., t. xvi., 1891).

Spitzka, E. C., Contributions to the anatomy of the lemniscus, Medical Record, 1884.

Sutton, J. B., The lateral recesses of the fourth ventricle ; their relation to certain cysts and
tumours of the cerebellum, and to occipital meningocele, Brain, 1886.

Tooth, H. H., and Turner, "W. A., Study of a case of bulbar paralysis, with notes on the origin
of certain cranial nerves, Brain, 1891.

Vejas, P., Experimentelle Beitrage zur Kenntniss der Verbindungsbahne des Kleinhirns und des
Verlauf s der Funiculi gracilcs und cuneati, Archiv fiir Pyschiatrie, xvi., 1885.

Vincenzi, L., Note histologique sur I 'origine reelle de quelques nerfs cerebraux, Arch. ital. de
biologic, 1884.

Virchow, H., Ueber die Stria} acustica; des Menschen, Verhandl. d. phys. Gesellsch. zu Berlin,
Arch. f. Anat. u. Physiol., 1888. Physiol. Abtheil.

"Werdrig, G., Concrement in der recMen Substantia nigra Soemmeringii mit auf- und absteigender
Degeneration der Schleife und theilweiser Degeneration des Hirnschenkelfusses, Wiener med. Jahr-
bucher, Bd. viii., 1889.

Wilder, Burt GK, Notes on the foramina of Magendie in Man and the Cat, Journal of Nervous
and Mental Disease, vol. xiii., 1887.

THE CEREBELLUM.

69

THE CEREBELLUM.

The cerebellum (figs. 55, 56, and 58) consists of two lateral hemispheres joined
together by a median portion called, from the peculiar appearance caused by the
transverse furrows or ridges upon it, the worm or vermiform process. This is seen

Fig. 55. — INFERIOR SURFACE OF
THE CEREBELLUM WITH THE
PONS VAROLII AND MEDULLA
OBLONGATA. (From Sappey after
Hirschfeld and Leveille.) |

1,1, inferior vermiform pro-
cess ; 2, 2, median depression or
vallecula ; 3, 3, postero-inferior
lobe of the hemisphere ; 4, amyg-
dala ; 5, flocculus ; 6, biventral
lobe ; 7, pons Varolii ; 8, middle
peduncle of the cerebellum ; 9,
medulla oblongata ; 10, 11, ante-
rior part of the great horizontal
fissure; 12, 13, smaller and larger
roots of the fifth pair of nerves ;
14, sixth pair ; 15, facial nerve ;
16, pars intermedia ; 17, auditory
nerve ; 18, glosso-pharyngeal ;
19, pneumo-gastric ; 20. spinal
accessory ; 21, hypoglossal nerve.

on the under surface in the fossa between the hemispheres as a well-marked pro-
jection named the inferior warm, but above forms only a slight elevation, the
superior worm. In birds, and in animals lower in the scale, this middle part of the
cerebellum alone exists, and in mammals it is the first part to be developed and to be
marked off into subdivisions ; moreover, in most mammals it forms a large median
lobe very distinct from the hemispheres.

The cerebellum occupies the posterior fossa of the cranium. Its median portion
lies behind the 4th ventricle and behind and below the corpora quadrigemina, to

Fig. 56. — LOWER SURFACE OF THE

CEREBELLUM WITH THE INFE-
RIOR (POSTERIOR) MEDULLARY
VELUH. (Allen Thomson after
Reil and Reichert, and from
nature. ) |

The medulla oblongata is cut
across near the pons Vavolii ; and
the latter has been separated
somewhat from the cerebellum in
order to bring into view the pos-
terior medullary velum. To dis-
play this better the amygdalae
have been removed.

/ h, horizontal fissure ; p s,
postero-superior lobe ; p i and ff,
postero-inferior lobe ; g, slender
lobe ; b i, biventral lobe ; /, flocculus ; c to n, inferior vermiform process, on which are, c, tuber
valvulae, p, pyramid, u, uvula, n, nodule ; p v, on each side, placed on the cut surface where the
amygdalae have been removed, points by a line to the lateral part of the inferior (posterior) medullary
velum ; its median part is lost under the nodule ; v, v, cavity of the fourth ventricle ; the cavity
extends on each side into the lateral recess ; m, cut surface of medulla oblongata ; V, VI, roots of the
fifth and sixth cranial nerves.

which it appears suspended by its superior peduncles. Below and at the sides it
receives the inferior peduncles (restiform bodies) from the medulla oblongata, and

70

THE CEREBELLUM.

from the anterior part of each hemisphere the thick mass of the middle peduncle
passes forwards and inwards into the pons Varolii. Between the two superior
peduncles and behind the upper part of the 4th ventricle is a white lamina con-
tinuous with the white centre of the worm, which thins off into it. This is the
superior (or anterior) medullary velum or valve of Vieussens ; it extends as far as
the corpora quadrigemina, filling up the interval between the superior peduncles,

for.Mon

forni

traneu.figg.

pineal stria
post. comm.
pineal

ileniitm

monttcwlu.8

ualu

pjrar

Fig. 57. — PORTION OF A MEDIAN SECTION OF THE BRAIN, SHOWING THE CORPUS CALLOSUM, THIRD

VENTRICLE, AQUEDUCT AND FOURTH VENTRICLE, PONS, CEREBELLUM, &C. (G. D. T.) 2

and becoming continued into the roof of the aqueduct of Sylvius. Below, there is
a similar white lamina prolonged under and on either side of the nodule from the
white centre, and stretching over this part of the ventricle towards its lateral
boundaries (fig. 56, p v). It does not, however, extend far down, but ends with a
somewhat thickened margin, concave downwards, being prolonged towards the
calamus scriptorius merely by the ventricular epithelium, which covers its ventral
surface. To the semilunar lamina thus formed the name inferior (or posterior)
medullary velum is applied.

The hemispheres are separated below and behind by a deep notch (posterior
ccrebellar notch, incisura marsupialis), and above and in front by a broader, shallower
notch (anterior cerebellar notch, incisura semilunaris). The upper vermiform process,
although slightly elevated, is not sharply marked off from the dorsal surface of the
hemispheres, so that the upper surface of the organ, which is on the whole flattened
but somewhat ridged in the middle (culmen monticuli), slopes downwards uninter-
ruptedly cii each side and behind (clivus). On the inferior surface each hemisphere
is convex both from before backwards and from side to side, but is separated
from its fellow by a deep median fossa, named the vallecula, which is continuous
behind with the posterior notch, and in which the inferior vermiform process
(fig. 56, c to n, fig. 58 B, t.v. to n.) lies concealed. Into this hollow the medulla
oblongata is received in front, and the falx cerebelli behind.

THE CEREBELLUM. 71

The greatest diameter of the organ is transverse, and extends to about four inches
(10 centimeters) : its greatest width from before backwards is about two inches (5
centimeters) : of the middle part about one inch and a half (4 centimeters) ; and
its greatest depth is about two inches, but it thins out towards the lateral border.
It weighs about 5 oz.

The cerebellum is characterised by its laminated or foliated appearance, its
surface being everywhere marked by deep, closely set, transverse and somewhat
curved, fissures, which extend a considerable depth into its substance, but do not all
entirely encircle the organ, for many of them coalesce with one another, and some
of the smaller furrows have even an oblique course between the others. Moreover,
on opening the larger fissures, other folia are seen to lie concealed within them, not
reaching the surface of the cerebellum.

The depth of the fissures can best be estimated in sections through the organ
taken across the laminae : in such sections each lamina is seen to have a white
centre and a grey cortex, and the white centres of the laminee appear in the form of
processes ramifying from a larger white centre near the middle and anterior part of
the organ : to the arborescent appearance thus obtained in section the name arbor
vitce, cerelelli has been applied.

Externally the most conspicuous fissure is the great horizontal fissure (figs.
56, 58, fh), which beginning in front at the middle peduncle of either side
extends round the outer and posterior border of each hemisphere, dipping down into
the posterior notch. This fissure divides the cerebellum into an upper and lower
portion, corresponding in fact to the upper and lower surfaces, in each of which
several lobes, separated by fissures for the most part deeper than the rest, are
described. Taking the great horizontal fissure to divide the cerebellum into an
upper and a lower half or surface, we may first consider the parts which are present
upon the upper surface and which .compose the upper half of the organ in both the
worm and the hemispheres.

UPPEE SURFACE. — The upper worm begins at the superior medullary velum
between the two superior peduncles and ends at the bottom of the posterior notch in
a short, concealed transverse lamina, termed the folium cacuminis. It is usually
described as being formed of five successive parts or lobules, which are termed from
before back the lingula, the central lobe, the culmen (culmen monticuli), the clivus
(clivus monticuli), and the folium cacuminis. Corresponding with these in each
hemisphere are the large poster -o- superior lobe, continued laterally from the small
folium cacuminis, the posterior crescentic, continued from the clivus, the anterior
crescentic lobe, continued laterally from the culmen, the ala loibuli centralis, continued
from the central lobe, and sometimes a lateral extension of the lingula.

Of the fissures which separate these lobes of the upper surface from one another,
four in number, the first, or most anterior, which may be termed the precentral
sulcus, lies in front of the central lobe, and separates it from the lingula. The
next, or postcentral sulcus, divides the central lobe and its alas from the culmen
and anterior crescentic lobes. The third, or preclival fissure (also called the antero-
superior), separates the culmen and anterior crescentic from the clivus and posterior
crescentic lobes. Lastly, the fourth, or postclival fissure (also called the postero-
superior), lies immediately over the folium cacumiuis, and separates this and the
postero-superior lobes from the clivus and posterior crescentic. Below the folium
cacuminis and the postero-superior lobes comes the great horizontal fissure which
has been already described.

Besides these interlobar fissures, all of which extend deeply down towards the
central white substance, there are certain other sulci which on the upper surface
of the hemispheres are almost or quite as well marked as the interlobar ones, but
which are less deep or are not seen on the upper worm. They are best made out in

THE CEREBELLUM.

vertical sections of the hemisphere. Two of these intralobar fissures occur in the
posterior crescentic (clival) lobe and one or two in the anterior crescentic (culmi-

A.

S.pr.-cl. 7

* i t-.m.

Fig. 58. — VIEWS OF THE UPPER (A) AND LOWER (B) SURFACES OF THE CEREBELLUM, NATURAL SIZE.

FROM PHOTOGRAPHS. (E.A.S.)

In A. l.c, lobulus centralis ; a.l.c, ala lobuli centralis ; TO, culraen monticuli ; l.m, lobus
culminis ; d, clivus ; l.d, lobus clivi ; l.eac, lobus cacuminis ; l.t, lobus tuberis ; s.p.-c, sulcus post-
centralis ; s.pr.-cl, sulcus preclivalis ; s.p.-cl, sulcus postclivalis ; f.h, f.h, fissura horizontalis magna.

In B. . I, lingula ; Z.c, lobulus centralis; a.l.c, ala lobuli centralis; s.p.-c, sulcus postcentralis ;
v.m.s, velum medullare superius ; p.s.c, pedunculus cerebelli superior ; p.c, peclunculi cerebelli medius
et inferior ; n, nodulus ; v.m.i, velum medullare inferius ; p.fl, pedunculus flocculi ; fl, flocculus ; u,
uvula ; am, amygdala ; py, pyramis ; l.biv, lobus biventralis ; t.v, tuber valvulse seu posticum; l.t,
lobus postero-inferior ; l.gr', lobulus gracilis anterior ; l.gi'2, lobulus gracilis posterior ; s.pr.-gr, sulcus
pregrrtcilis ; s.i.-gr, sulcus intra-gracilis ; s.p.-gr, sulcus postgracilis ; f.h, fissura borizontalis magna.

The vallecula has been somewhat opened out to display the parts of the lower worm.

nate) (fig. 59). The laminae and fissures of the upper surface all have a subparallel
transverse direction, curving forwards as they traverse the hemisphere to lose them-
selves at the antero-lateral border in the great horizontal fissure.

CLIVUS AND POSTERIOR CRESCENTIC LOBES. 73

Lobes of the upper surface. — We may now describe in detail the subdivisions
of the upper surface, taking (since they are directly continuous with one another)
those of the worm and hemispheres together.

The lingula. — This is usually confined to the worm, and from the surface it is
entirely concealed by the next lobe : it is best seen in a median section of the organ
(figs. 57 and 59). It consists of a small tongue-shaped group of four or five trans-
verse laininse, which may be said to lie upon the middle of the superior medullary
velum (fig. 58, I). Its medullary centre is in continuity with the velum, and
forms part of the roof or dorsal boundary of the fourth ventricle which here has a
tent-shaped projection into the middle of the cerebellum (fig. 57, 4).

The lingula gradually shades off at the sides and is usually unrepresented in the
hemispheres, but its laminae are sometimes prolonged laterally for a little distance
over the superior cerebellar peduncle (frcenulum linyulcc}.

The central lobe and its alae. — The central lobe is largely concealed by the
culmen when the cerebellum is in its natural position, but when the organ is cut
away from the adjacent structures this lobe is seen in the anterior notch, where
its laminae appear at the surface. They are prolonged beyond the limit of the worm,
for some distance along the upper and anterior part of the hemispheres, where
they form wing-like continuations of the central lobe which are known as the
alee lobuli centralis (fig. 58). The central lobe receives a primary branch of the
arbor vitas which passes upwards and forwards into it from the enlargement of
the white centre which is known as the trapezoidal body, but the fissures (pre-
central and postcentral) which separate it from the lingula and culminate lobe
respectively, are not better marked at the surface than those which intervene
between the laminae of the culminate lobe, and, as a glance at the sections (fig. 59)
shows, its laminae all belong to the same (ascending) group of folia as those which
constitute the culminate lobe.

The culmen and anterior crescentic lobes : lobus culminis. — The culmen
occupies rather more than half of the upper surface of the worm, and, as its name
implies, constitutes the most prominent part of the upper worm. Its surface shows
three or four well-marked lamellae, beset by a number of secondary and tertiary folia.
'It is separated from the next part of the worm by a deep groove which descends to
the middle of the organ ; this sulcus is prolonged, as we have already seen, on to
either hemisphere, having there been termed the antero-superior sulcus, and passing
in a curved manner parallel with the general disposition of the laminae on this sur-
face to the antero-lateral margin, where it runs into the anterior part of the great
horizontal fissure. The antero-superior sulci together may conveniently be termed
the preclival. The subdivision of the hemisphere which is cut off between this
preclival fissure behind and the postcentral sulcus in front has been known as the
anterior crescentic lobe (lobus lunatus anterior, Ko'lliker). The two anterior crescentic
lobes, together with the culmen with which they are in complete lateral continuity,
form a main subdivision of the upper surface of the cerebellum, which may appro-
priately be termed the lobe of the culmen. The lateral parts of the lobe each receive
three well-marked branches of the medullary centre of the hemispheres ; in the
central part they come off by a common stem from the corpus trapezoides of the
worm (fig. 59).

The clivus and posterior crescentic lobes : lobus clivi. — Behind the
antero-superior or preclival fissure, and extending as far as the folium cacuminis
(from which it is separated by the postero-superior or postcUval fissure), is another
considerable group of laminae which receive their branches from the upper aspect of
the horizontal stem of the arbor vitae. In a median section of the worm these
laminae appear to form one group with the folium cacuminis and the laminae of the
tuber valvulse (fig. 59 A), and this group has been described by Schwalbe as con-

74 THE CEREBELLUM.

stituting a posterior lobe. In fact, however, the great horizontal fissure below the
folium cacuminis and the postclival fissure above this folium separate the group
into three well-marked divisions, of very unequal size it is true in the worm, owing
to the rudimentary character of the central or cacuminate division, but far more
distinct and equal in the hemispheres ; they may therefore be conveniently thus
subdivided in the worm also, and of them, two (the clivus and folium cacuminis)
belong to the upper worm, the third, tuber valvulse, to the lower.

Two or three secondary laminae. of the clivus reach the surface of the worm, but
they are beset with many tertiary folia, and other important folia belonging to the
same group lie concealed in the preclival fissure.

The lateral extension of the clivus on to each hemisphere is known as the
posterior crescentic lobe (I. lunatus posterior, Kolliker), and the two posterior
crescentic lobes with the clivus between them, bounded in front by the preclival,
behind by the postclival fissure, may collectively be termed the lobe of the clivus.
The lateral parts of this lobe each receive two or three primary branches of the
medullary centre of the hemisphere (fig. 59).

The combined anterior and posterior crescentic lobes of each, hemisphere were formerly
termed the quadrilateral lobe.

The folium cacuminis and postero-superior lobes : lobus cacuminis.

—The folium cacuminis is formed by the extremity or apex of the main horizontal
stem of the arbor vitse vermis (figs. 57, 59). As the vertical section shows, it is
composed of but a single primary folium, which may be either plain or beset
with rudimentary folia. But at the side of the worm it rapidly expands, with
divergence of its bounding fissures and a great increase of size of its main branch of
the arbor vitae and the formation of numerous secondary and tertiary folia, a large
lobe being thereby produced at the posterior and upper part of each hemisphere
which has been termed the postero-superior lobe. The expansion occurs mostly
above the horizontal plane, and its branch of the arbor vitas has a direction no longer
directly backwards, but rather upwards and backwards ; this upward shifting
appears to be due to the great development of the lobes of the lower surface of the
hemisphere. The postero-superior lobes are bounded, like the folium cacuminis itself,
in front and above by the postclival fissure, below by the great horizontal fissure ;
joined as they are in the middle line by the folium cacuminis, they form a great
winged mass which occupies the posterior third of the upper surface of the cerebellar
hemispheres, and forms the rounded postero-lateral border ; to this conjoined mass
the term lobus cacuminis may be applied.

UNDER SURFACE. — Turning now our attention to the under surface of the
organ, we here meet with considerably greater complexity, and the correspondence
between the parts of the worm and those of the hemisphere is less clearly apparent.
The lower worm extends from the inferior medullary velum to the folium cacuminis
(great horizontal fissure), and the parts or lobules which are enumerated in
it are four in number, viz. : from before back (1) the nodule, (2) the uvula,
(3) the pyramid, and (4) the tuber valvulce, seu posticum. On the hemisphere a
greater number of lobes are distinguished, viz. : (1) the flocculus, corresponding
with the nodule ; (2) the tonsil (amygdala), corresponding with the uvula ;
(3) the bi-ventral lobe, corresponding with the pyramid ; (4) the slender lobe, formed
of an anterior and a posterior part well marked off from one another ; and (5) the
inferior semiltmar lobe, which also shows a tendency to subdivision. This
last lobe corresponds with and is directly in lateral continuity with the tuber
posticum of the worm. The slender lobes are interpolated in the hemisphere, and
have not any obvious prominence of the worm corresponding with them, but they
appear to represent a development of certain rudimentary folia which are seen in

NODULE AND FLOCCULUS. 75

sagittal sections of .the worm on the lower part of the stalk of the tuber valvulse,
entirely concealed by the pyramid (see fig. 59 B). If this is the case, then the com-
bined slender and inferior semilunar lobes may be reckoned as collectively forming
a primary subdivision of the hemisphere, corresponding with the tuber posticum
of the worm and to which the term postero-inferior may be applied,1 and the two
postero-inferior lobes, together with the tuber valvulae which unites them in the
middle line, may collectively be spoken of as the lobus tuberis. This large lobe
occupies at least two-thirds of the inferior surface of the cerebellum ; of the re
maining third more than one-half is occupied by the combined pyramid and biven-
tral lobes, about one-third by the uvula and amygdalae, and the small remaining
portion by the nodule and flocculus.

Fissures of the under surface. — The lobes of the under surface of the
organ are separated from one another by fissures extending deeply into both the
worm and hemispheres. In the worm there are three such interlobar depressions,
viz. : one between the nodule and the uvula (postnodular), one between the uvula
and pyramid (prepyr -amidol*), one between the pyramid and tuber valvulae (post-
pyramidal), besides the middle of the great horizontal fissure separating the tuber
valvulas from the folium cacuminis. In the hemispheres a larger number is
apparent. The postnodular sulcus passes laterally into a groove curved with its
convexity forwards which first limits the amygdala in front and then passes between
the flocculus and biventral lobe to join the anterior end of the great horizontal
fissure. The prepyramidal sulcus curves laterally round the outer side of the
amygdala^ separating it from the biventral lobe : it joins the postnodular in front
of the amygdala. From the sides of the postpyramidal sulcus three deep fissures,
concentric with one another, curve outwards and forwards over the under surface of
the hemisphere. The most anterior of these, and also the shortest, passes at first
more forwards, concealed by the amygdala before curving round in the manner
described. It lies between the biventral and slender lobes, and may be termed the
anterior arcuate or pregracile sulcus. The second of the three concentric fissures
subdivides the slender lobe into two nearly equal parts (lobulus gracilis anterior and
lobulus gracilis posterior) ; we may distinguish it as the middle arcuate or mid-
yracile. The third, which is the longest, separates the slender lobe from the
inferior semilunar lobe ; like the other two it arises at the mesial edge of the hemi-
sphere opposite the depression (postpyramidal sulcus) between the pyramid and the
tuber valvulae, and arches round on the lower surface of the hemisphere with its
concavity forward to fall into the great horizontal fissure at the antero-lateral margin.
This fissure may be termed the posterior arcuate or postgracile. Behind this
again there is a fairly well marked deep fissure, serving to subdivide the inferior
semilunar lobe. This may be termed the lower or lesser horizontal sulcus. Lastly,
the deep antero-posterior grooves which mark off the lower worm may conveniently
be termed the sulci valleculm (dexter et sinister).

Lobes of the under surface. — The lobes of the under surface of the organ
as already enumerated may be now more particularly described in order from before
back.

The nodule and flocculus: lobus noduli. — The nodule occupies much the
same position relatively to the inferior medullary velum and tent of the fourth
ventricle that the lingula occupies with regard to the superior medullary velum, but it
is usually better developed than the lingula. Although sometimes merely composed
of a few transverse laminae set upon the median part of the inferior medullary velum,
it more often appears as a distinct prominence having a separate branch of the

1 In the previous edition of this work, the term postero-inferior was used as a synonym for the
inferior semilunar lobe.

76 THE CEREBELLUM.

arbor vitas (fig. 59 A). It can only be seen after the cerebellum is separated from
the medulla oblongata and pons, or in a median section, being almost entirely con-
cealed by the uvula when the organ is viewed from below. The lateral part of
the inferior medullary velum is continued on either side of the nodule as a thin
white semilunar band with a thickened concave free lower border (fig. 58 B, v.m.i).-
Traced laterally towards the hemisphere, the white lamella becomes thickened and
covered with grey matter (pedunculus flocculi), and at length expands into a small
irregular lobule lying in the groove between the biventral lobe and the middle
peduncle of the cerebellum, and composed of a few short irregular laminas, which
tend to diverge from the attachment of the stalk. The nodule, with the inferior
medullary velum, the stalk of the flocculus, and the flocculus itself constitute
collectively a small but distinct subdivision of the cerebellum (lolus noduli).

Other small portions of laminated grey matter sometimes 6ccur attached to the flocculus,
usually lying between it and the middle peduncle. These have been termed accessomj
ftocculi.

The uvula and tonsils : lobus uvulae. — The uvula forms a considerable
portion of the lower worm, being elongated from before back ; three considerable
secondary laminas, beset with eight or more tertiary folia, appear at the surface.
It is least prominent close to the nodule, and from this part it enlarges rapidly
downwards and backwards to attain its greatest prominence next to the pyramid.
Like the nodule and the pyramid it is purely a median prominence, being separated
from the hemispheres by the deep groove (sulcus valleculse) which prolongs the
vallecula on either side of this part of the worm. At the bottom of this groove
on either side of the uvula is a low corrugated greyish ridge which connects the
narrow stalk of the uvula with the stalk of the tonsil : this concealed connecting
ridge is known as the furrowed band. From its outer extremity the rounded
amygdala projects downwards and backwards into the vallecular groove, concealing
the sides of the uvula mesially, and the narrow connection between the pyramid
and biventral lobe posteriorly. The uvula, furrowed band and tonsil constitute col-
lectively another distinct subdivision of the hemisphere (amygdalo-uvular lobe, lobus
uvulcc). The amygdala or tonsil forms a rounded projection of about 10 or 12
folia, which run nearly in a sagittal direction, so that in a sagittal section of the
cerebellum passing through the tonsil, its branch of the arbor vitas appears expanded
and not obviously dendritic (fig. 59 C). Above and in front it has a few transverse
laminae which are only seen in sections, being concealed, in the natural position of
the parts, by the rest of the projection. Opposite the inferior medullary velum
its white matter comes for a certain distance to the surface, covered, of course, by
pia mater. The amygdala is lodged in a depression (nidus avis) at the front of the
vallecula, which is bounded by the uvula mesially and the biventral lobe laterally ;
the surface which rests against the uvula is nearly smooth, as is the corresponding
concave surface of the uvula ; a continuation of the postnodular sulcus separates
it from the inferior medullary velum.

The pyramid and biventral lobes : lobus pyramidis. — The pyramid forms
the most marked prominence of the lower worm, but as seen from the surface, it
shows only three or four transverse laminae. It is in reality a long clavate projection
attached to the stem of the arbor vitas by a narrow stalk, and it is not only separated
from the uvula and tuber valvulas by deep fissures, but also from the hemispheres
by the sulcus valleculae on either side of it. Its connection with the biventral lobe
of the hemisphere is here maintained by a low narrow ridge, which joins the stalk
of the pyramid with the mesial pointed extremity of the biventral lobe. This
connecting ridge is evidently analogous with the furrowed band of the preceding
lobe, but it is an even less distinct structure. To see it the amygdala must be

THE TUBER VALVUL^. 77

removed, or a vertical section made through the organ, passing just to the outer
side of the pyramid. The biventral lobe is roughly triangular in shape, with
the base forwards abutting on the postnodular sulcus, and the apex directed
backwards and inwards towards the root of the pyramid. The outer side is
bounded by the outwardly curved pre-gracile fissure, the inner by the side of
the vallecula, but is concealed by the amygdala, which projects over the lobe.
The laminse have a curved direction radiating from the apex towards the base of the
triangle. The lobe is partly bisected by a fissure (midventral) deeper than the
rest, and becoming better marked towards the base. This fissure divides the lobe
into an inner and an outer portion ; from this subdivision its name has been
derived. Collectively, the pyramid, the connecting ridges, and the biventral lobes
constitute a distinct division of the cerebellum, to which the name lobe of the
pyramid may be applied.

The tuber posticum and postero-inferior lobes : lobus tuberis. — The
tuber valvulse seu posticum, which constitutes the hindermost division of the inferior
worm, exposes about five or six tertiary folia (laminse transversales inferiores) at
the surface between those of the pyramid and the folium cacuminis. It differs
from the other constituents of the inferior worm, and resembles those of the
superior worm in being obviously prolonged laterally into and gradually enlarging
to form the corresponding hemisphere lobes (fig. 58 B, t.v, l.t). These conjoined
postero-inferior lobes of the hemispheres with the tuber valvulas of the worm
collectively form a large alate mass (lobus tuberis}, bounded in front by the
anterior arcuate or pregracile fissure, which separates it from the pyramidal
(biventral) lobe ; behind by the great horizontal fissure, which also limits it
antero-laterally. Its laminae run in a curved manner, concentrically with these
fissures, and it is separated into four crescendo parts by three concentric fissures
two deep and complete, the middle arcuate and the posterior arcuate and a third
only slightly less deep, the lesser horizontal fissure. Of these four parts the two
anterior, about equal in size, form what has been termed the slender lobe (lobus
gracilis) ; the two posterior, of which the hinder one is the larger, together form
what has been termed the inferior seniilunar lobe.

The whole cerebellar worm may thus be regarded as subdivided by deep sulci into nine
parts or lobes, each of which has a corresponding lobe of the hemisphere continuous with it.
This continuity is obvious upon the upper and posterior aspects of the organ, but on the inferior
aspect it tends to be rudimentary and is moreover concealed within the sulci valleculae. The
combined lobes which are thus formed by the continuity of the lobes of the worm with those
of the hemispheres are as follows : — (1) lobus lingulas, (2) lobus centralis, (3) lobus culminis.
(4) lobus clivi, (5) lobus cacuminis, (6) lobus tuberis, (7) lobus pyramidis, (8) lobus uvulse,
and (9) lobus noduli. The hemisphere-parts of the lobus lingulas and of the lobus centralis
are rudimentary, but otherwise the hemisphere-parts of the lobes are considerably larger than
those of the worm, in some cases, as in that of the lobus cacuminis and the lobus tuberis. the
difference of size being very great. The former (lobus cacuminis) is, in fact, represented in
the worm by a single concealed folium only, while a large portion of the lobus tuberis, viz.,
the lobus gracilis, can hardly be said to be represented in the worm. These nine lobes are
separated from one another by interlobar fissures, which are all nearly equally well marked in
the hemispheres, whilst in the worm some are less developed, particularly those above and
below the folium cacuminis. This median part of the lobus cacuminis is, therefore,
imperfectly marked off from the clivus above and the tuber valvulas below, the three together
forming a very distinct posterior subdivision of the worm.

The relations between the parts of the worm and those of the hemispheres, and the fissures
which separate the several lobes from one another, as well as those which serve to subdivide
the lobus tuberis, are indicated in the accompanying table : —

78

THE CEREBELLUM.

DIAGRAMMATIC TABLE to show the corresponding parts of the worm and hemispheres and
the fissures which separate them into lobes. The positions of the principal intra-lobar
fissures of the hemisphere are marked by thin lines.

WORM AND
HEMISPHERE.

Sulcus precentralis. .

Sulcus postcentralis

Sulcus preclivalis

Sulcus postclivalis

Sulcus horizontalis )
magnus )

Sulcus postgracilis

Sulcus intragracilis ...

Sulcus pregracilis )
s. postpyramidalis j

Sulcus prepyramidalis . .
Sulcus postnodularis . .

HEMISPHERE.

WORM.

Fraenulum lingulas

Lingula

Ala lobuli centralis

Lobulus
centralis

Lobus
lunatus
anterior

Culmen
monticuli

Lobus

lunatus
posterior

Clivus
monticuli

Lobus
postero-superior

Folium
cacuminis

Lobus
semilunaris ^

inferior g*
5

Tuber
valvulee

Lobulus
gracilis

anterior o '

Lobulus
gracilis 5'
posterior ""*

Lobus
biventralis

Pyramis

Amygdala

Uvula

Flocculus

Nbdulus

Lobus lingrulse

Lobus centralis

Lobus culminis

Lobus clivi

Lobus cacuminis

Lobus tuberis

Lobus pyramidis

Lobus uvulae

Lobus noduli

Description of the arbor vitae cerebelli. — When a section is made through
the worm or through either hemisphere across the direction of the folia, the organ is
seen, as already mentioned, to be composed of a white or medullary centre and of a
uniform cortex of grey matter, and the section presents a dendritic appearance
(arbor vitae cerebelli) in consequence of the fact that the larger laminae are them-
selves formed of secondary, and these again are beset with tertiary folia. It is
only in such sections that the relative depth and importance of the fissures can be
estimated, and a description of the sections is therefore fully as important as that
of the surface-markings, and is in fact necessary for the elucidation of the latter.

The mode of transition of the parts of the worm into those of the hemispheres
can also best be made out by the inspection of successive sagittal sections ;
beginning with a median section through the worm, and passing gradually to the
side, the successive sections being made in planes parallel with the median plane, or
only so far inclined to it, and to one another, as to cut the majority of the lamellae
at right angles.

1. Section of the cerebellum in the median plane of the woi'tn (fig. 59 A, and
fig. 57). In front we notice the tent of the fourth ventricle projecting with a
sharp angle into the enlargement of the white substance known as the corpus
trapezoides (c.tr). The apex of the angle is directed backwards with a slight down-
ward tilt, so as to leave only a thin layer of white matter — the middle part of the
inferior medullary velum — between it and the nodule. The corresponding layer of

DESCRIPTION OF THE ARBOR VIT.E CEREBELLI. 79

white matter between the cavity of the fourth ventricle and the lingula is the
middle part of the superior medullary velum. The two vela are prolonged like roots
upwards and downwards from the anterior or ventral side of the corpus trapezoides.
From the upper part of the corpus trapezoides two branches diverge, one upwards
with a slight inclination forwards, this is the branch to the central lobe ; the
other, the thickest and strongest of all the branches of the arbor vitse of the
worm, passes upwards and backwards into the culmen. This stem of the culmen
gives off secondary branches on cither side. Of those which are directed upwards
and forwards, the one nearest the base is rudimentary, and enters a small lamina
concealed at the bottom of the post-central fissure : the next two are large, and
enter laminae which reach the surface, but before attaining it they may themselves
fork. The prolongation of the stem also reaches the surface, being first bifurcated,
but the branches from the lower or posterior side of the stem of the culmen, two,
three or more in number, pass into short laminae which mostly lie concealed within
the pre-clival fissure.

Prolonged backwards from the postero-inferior angle of the corpus trapezoides
is a narrow horizontal stem, which after a course of about two centimeters, ends
directly in the medullary centre of the folium cacuminis, often passing round a
slight curve just before reaching this. From the upper side of this horizontal stem
about five branches pass upwards and backwards, and from the lower side about
as many pass downwards and backwards, but all are not of equal importance, for
some merely enter rudimentary lamellae which are concealed at the bottom of the
interlobar fissures, and only a few enter lamellas which reach the surface.

Of those which pass from the upper side of the horizontal stem all may be
considered to belong to the clivus. Of the more anterior of these some are rudi-
mentary, one or two less so, but all enter lamellas which are completely concealed
in the preclival fissure. The hindmost is larger and longer and reaches the surface ;
it gives off a vertical branch which passes into the upper part of the lobe nearest
the culmen, bifurcating near the surface, and is then continued on in a nearly
horizontal direction parallel to and overlying the folium cacuminis.

Of the branches from the lower side of the white centre and its horizontal pro-
longation three are of great importance. The foremost one passes from the corpus
trapezoides almost vertically downwards for about six or eight mm. into the uvula,
giving off only small lateral branches ; it then gives off successively two or three
branches which course downwards and forwards, usually bifurcating before reaching
the surface. Only short branches are given off backwards from the main part of the
uvula stem.

About two or three mm. behind the branch to the uvula, that to the pyramid
passes off. This has a general direction downwards and backwards ; it gives off
lateral branches tis it proceeds, most of which are small, but one or two longer
branches come off on its anterior aspect and pass to the surface nearly vertically
downwards.

Following the horizontal stem back, two or three rudimentary offshoots are seen
entering small lamellae which are concealed within the postpyramidal fissure, until
finally, about 15 mm. from the corpus trapezoides and 5 mm. from the base of the
folium cacuminis, another considerable branch passes off at an acute angle, with a
curve forwards and downwards into the tuber valvulae. Its lateral offshoots, which
are at first short, become gradually longer, corresponding with the expanding form
of this lobe of the worm.

The deepest fissures of the median section are the precentral, the postcentral,
the preclival, the prepyramidal, the postpyramidal, and the postnodular (see
fig. 59 A). The postclival fissure is here quite shallow, the great horizontal only
slightly deeper. The general grouping of the branches of the arbor vitae is into

80

suZcus

THE CEREBELLUM.

A

ven.tricu.lus
2V

Lotus
Cu.lm.inis

lobult,

Fig. 59. — FOUR SUCCESSIVE SAGITTAL SECTIONS OF THE CEREBELLUM TO SHOW ITS INTERNAL STRUCTURE,

THE RELATIVE DEPTH OP THE FISSURES, AND THE GROUPING OF THE LAMINA. (E. A. S.) Nearly

twice the natural size. (From photographs. )

A, meduin section of the worm.

B, section iiear the edge of the worm at the transition into the hemisphere.

C, at the edge of the hemisphere.

D, through the middle of the hemisphere.

DESCRIPTION OF THE ARBOR VIT^E CEREBELLL

81

Idbus djJ.rn.in.is

lobus
ca,cu>-mln.L

diet, lolulL

82 THE CEREBELLUM.

five divisions (irrespective of the white matter of the lingula and nodule), viz., two
ascending (central lobe and cnlmen), a posterior group (clivus, folium cacuminis,
and tuber valvulse), and two descending (pyramid and uvula).

2. Arbor vita at transition of tvorm into hemisphere (fig. 59 B). With the
general enlargement of the organ as the worm passes into the hemisphere the white
centre becomes greatly increased in amount. This affects all parts of it, but first
and most markedly the corpus trapezoides and the root of the branch into the
culmen, which is here a large square mass of white matter from which three distinct
branches pass towards the upper surface of the culmen, which is subdivided by two
deep fissures (anterior and posterior intraculminate) into as many parts. A short
branch also passes forwards from the corpus trapezoides into the ala lobuli centralis.
The lingula is still seen in this section, and the superior medullary velum is
becoming thickened by the fibres of the superior cerebellar peduncle. The
horizontal stem of the arbor vitas is also much thicker, and from it the branches
of the clivus pass upwards as two main stems, which go towards the surface,
bifurcating as they approach it ; there are concealed folia in the pre- and post-
clival fissures. The postclival fissure is now deep, as is also the great horizontal,
and between the two a lobe, fan-shaped in section (the postero-superior), is now
visible, having a distinct large bifid branch of the arbor vitse directed upwards and
backwards into it, each ramus dividing more than once before reaching the surface.
Between the great horizontal and the postpyramidal fissure a large branch passes
downwards and backwards, and gives off several well-marked rami from its lower
border, three or more reaching the surface. The branch into the pyramid is broader
at its root ; in fig. 59 B, the section passes outside the uvula, and has taken a slice
off the amygdala.

3. In a sagittal section altogether beyond the vermis and just within the limit
of the hemisphere, what in the worm constitutes the horizontal stem of the arbor
vitae, has become greatly enlarged, and has now blended with the enlarged corpus
trapezoides to form the large central white mass of the hemisphere (fig. 59 C).
In this the nucleus dentatus is now seen, and appears as a thin irregularly triangular
wavy band of grey matter, with the blunt apex of the triangle directed posteriorly
towards the horizontal fissure and the open base looking forwards and receiving the
great mass of fibres of the superior cerebellar peduncle which now replaces the
superior medullary velum. Above the level of the horizontal fissure seven or eight
principal processes of the white centre extend into the lobes of the upper surface :
the most anterior is small, and passes forwards into the diminishing ala lobuli
centralis ; three enter the anterior crescentic lobe (in the section here figured they
still appear to come off from a common stalk) ; two or three, the posterior crescentic ;
and a large branch directed obliquely upwards and backwards passes into the
postero-superior or cacuminate lobe : between these principal branches are a few
rudimentary ones passing into concealed lamellse, of which there are groups at the
bottom of the pre- and postclival fissures. Besides the postcentral and the pre- and
postclival fissures, two other fissures divide the anterior crescentic lobe into three
parts, and other fissures divide the posterior crescentic. The cacuminate lobe is not
thus subdivided by complete fissures.

Below the level of the great horizontal fissure six or seven main branches come
off from the white centre. Two of these pass into the inferior semilunar lobe ;
one, the posterior, being very large and bifid or trifid ; one passes into each division
of the lobus gracilis, one into the biventral lobe, and a broad anteriorly directed
branch into the amygdala. A seventh small offshoot, directed almost due forward,
belongs to the stalk of the flocculus. In sections still further outwards (fig. 59 D)
the conditions are much the same as here described, except that the ala lobuli
centralis, and the amygdaloid branch are no longer seen, and the branch into the

THE DENTATE NUCLEUS.

83

biventral has become distinctly bifid. The nucleus dentatus does not extend far
into the lateral part of the hemisphere, and the superior cerebellar peduncle is no
longer cut ; but fibres are seen streaming from the white centre of the hemisphere
into the middle and inferior peduncles. The general conformation of the section
is somewhat altered, but the number and relations of the sub-divisions of the
hemisphere is not materially different, and the several branches of the arbor vitee
and the more important fissures are readily recognizable.

Nuclei in the white matter of the cerebellum. — The dentate nucleus
(corpus ciliare, corpus dentatum) of the cerebellum (figs. 59 C, and 60, n.d.), very

n.gZobosu.s

jjle

Fig. 60. — SECTION ACROSS THE CEREBELLUM AND MEDULLA OBLONGATA SHOWING THE POSITION OP THE

NUCLEI IN THE MEDULLARY CENTRE OF THE CEREBELLUM. (Stilling.) -f.

n.d., nucleus dentatus cerebelli ; s., band of fibres derived from restiform body, partly covering the
dentate nucleus ; s.c.p., commencement of superior cerebellar peduncle ; com', com", commissural fibres
crossing in the median white matter.

similar to that already described in the olivary body of the medulla oblongata,
presents the appearance of a waved line of compact yellowish brown substance,
containing white matter within. The wavy character is more apparent in horizontal
than in vertical sections through the hemisphere. The line is interrupted at its
anterior and mesial part (hilum), where the superior cerebellar peduncle emerges
from it. The dentate nucleus may be described as consisting of a plicated pouch or
capsule of grey substance open at one part and enclosing white matter in its interior,
like the dentate nucleus of the lower olivary body.

In addition to the corpus dentatum certain other portions of grey matter, which
have been only more recently recognised, are found in the white centre of the
cerebellum (Stilling). They are three in number on each side and are termed
respectively the nucleus emboliformis, nucleus globosus, and nucleus fastigii (figs. 60.
61). The nucleus emboliformis is a small clavate mass of grey substance lying
mesially to and partly covering the hilum of the dentate nucleus. On the inner side
of the nucleus emboliformis, between it and the middle line, is a streak of grey
matter passing antero-posteriorly and ending behind in an enlarged extremity. This
has been named the nucleus globosus. Finally, close to the middle line, where

o 2

THE CEREBELLUM.

it is only separated from its fellow by a narrow septum of white matter, is a rather
larger portion of grey substance, which lies in the anterior part of the white centre
of the worm, and close to the upper wall of the tent-like projection in the roof of
the fourth ventricle. It is termed the nucleus of the roof or nucleus fastigii.

Fig. 61. — HORIZONTAL SECTION THROUGH

THE WHITE CENTRE OF THE CEREBELLUM,
SHOWIKG THE NUCLEI OF GREY MATTER.

(From Henle, after Stilling. ) f

The section is taken just over the roof of
the fourth ventricle. The nuclei are repre-
sented lighter than the white matter in which
they are embedded.

C d, corpus dentatum ; x, nucleus emboli-
formis ; y, y, nucleus globosus ; z, nucleus
fastigii. Above the two coalesced roof-nuclei
are seen some of the fibres of the superior
(anterior) decussation, and above these again
the laminae and furrows of the lingula (Lg) ;
whilst below the roof-nuclei one or two
laminae and furrows of the inferior vermiform
process are included in the section. Ccq,
superior cerebellar peduncle.

These several portions of grey matter
are not entirely isolated, but are
connected here and there both with
one another and with the dentate
nucleus.

The structure of the corpus den-
tatum resembles that of the olivary body. Stellate cells -oVofch t° -oW-h incn
(6/ot to 10/t) in size, lie in grey matter which is traversed by bundles of nerve-fibres,
passing in various directions but chiefly from without inwards.

The nucleus emboliformis agrees closely in structure with the nucleus dentatus, to
which it seems to bear the same relation as do the accessory olivary nuclei to the
chief olivary nucleus. The nucleus fastigii and nucleus globosus differ somewhat in
structure from the dentate nucleus, and chiefly in the much larger size of their cells,
which, according to Meynert, are very similar to those of the nucleus of Deiters in
the medulla oblongata (see p. 56).

Commissural fibres in the white matter of the cerebellum. — Two chief
sets of decussating commissural fibres were described by Stilling in the middle line of
the cerebellum ; one at the superior part of the worm at the base of the central
lobule — the superior commissure (fig. 60, com') ; the other at the inferior part
(inferior commissure (com") ). Commissural fibres also pierce the nuclei of the
roof. In addition to these crossing fibres, which connect the two halves of the
white centre, other association fibres connect one lamina with another, passing
in the white substance of the laminae across their general direction, and arching
round the fissures between the laminas.

Peduncles of the cerebellum. — The cerebellar peduncles are constituted by
white fibres which pass out from or into the 'white medullary substance of the
hemispheres.

The superior peduncles (crura ad cerebrum) emerge from the upper and mesial
part of the medullary substance of the hemispheres, and run upwards and forwards
towards the corpora quadrigemina, under which they eventually pass and thus dis-
appear from the surface. They are situated at first at the side, but subsequently in
the roof, of the upper part of the fourth ventricle. These peduncles are concealed
by the upper part of the cerebellum, so that to see them properly this must be

THE CEREBELLAR PEDUNCLES.

85

divided in the middle line and turned aside. When this is done the superior crura,
with the superior medullary velum stretched out between them, are brought into
view. Their further course in the mid-brain will be subsequently traced.

The fibres of the superior peduncle pass almost entirely out of the interior of the
dentate nucleus (intraciliar fibres), but some fibres curve round the outer side of this
without passing into it (extraciliar), and some of the mesial fibres are traceable
directly into the white substance of the worm. Probably many of the fibres of
these peduncles which emerge from the dentate nucleus are connected with its cells,
but others pass in bundles through the grey lamina which composes it, without

Fig. 62. — FIGURE SHOWING THE THREE PAIRS

OP CEREBEIiLAR PEDUNCLES. ( From

Sappey after Hirschfeld and Leveille. )

On the left side the three cerebellar pe-
duncles have been cut short ; on the right
side the hemisphere has been cut obliquely
to show its connection with the superior and
inferior peduncles.

1, median groove of the fourth ventricle ;
2, the same groove at the place where the
auditory striae emerge from it to cross the
floor of the ventricle ; 3, inferior peduncle
or restiform body ; 4, funiculus gracilis ;

5, superior peduncle ; on the right side the
dissection shows the superior and inferior
peduncles crossing each other as they pass
into the white centre of the cerebellum ;

6, fillet at the side of the crura cerebri ;

7, lateral grooves of the crura cerebri ; 8,
corpora quadrigemina.

being thus connected. They appear to go eventually to the superficial grey matter
of the laminas.

From the superior medullary velum longitudinal fibres can be traced passing into
the white centre of the worm. These are chiefly fibres belonging to the antero-
lateral ascending cerebellar tract (see pp. 25 and 65).

Many, if not most, of the fibres of the superior peduncle originate in cells within the
cerebellum, and undergo degeneration as the result of lesions of that organ (see p. 93). But
in a case, reported by Mendel, of lesion of the left thalamus opticus, a well-marked bundle of
degenerated fibres was traceable through the tegmentum of the left side mesial to the nucleus
tegmenti, across to the right side at the deoussation of the superior peduncles, and along the
outer side of the right superior peduncle to the right hemisphere.

The middle peduncles (crura ad pontem), distinguished by the small size of their
fibres, coming from the pons Varolii, enter the lateral part of the white matter in two
main bundles. One of these, composed of the superior transverse fibres of the
pons which pass obliquely downwards over the others (fig. 30, »), radiates into
the lateral and lower parts of the medullary centre of the hemispheres. The
other bundle, which is formed of the lower transverse fibres of the pons, is joined
at its passage into the white centre by the restiform body or inferior peduncle
(fig. 30, &), and the fibres of both turn upwards and radiate into the upper parts
of the medullary centre of the hemisphere, and partly into the upper part of the
worm (but most of the pons fibres enter the hemisphere). Those peduncular
fibres which pass into the worm are derived chiefly from the restiform body, and
include the large fibres of the dorso-lateral cerebellar tract, most of which go to the
same side but some pass across to the opposite side. Those which enter the hemi-
sphere curve over the corpus dentatum, and are termed by Stilling the semicircular
fibres (fig. 60, s). They come mainly from the opposite olivary through the resti-
form body. A small part of the fibres of the restiform body is said by Stilling to
end in the corpus dentatum.

86 THE CEKEBELLUM.

The fibres of the middle peduncle, when traced ventralwards into the pons,
reach the middle line and there undergo decussation. After this intercrossing
many of their fibres appear to end in the grey matter which is so abundant in
the ventral part of the pons (nuclei pontis, fig. 49, n.p.). A certain number of fibres,
however, take a sagittal direction in the raphe and pass towards the reticular
formation, where they appear to give fibres to the posterior longitudinal bundle ;
by which means a direct connection seems to be established between the cerebellum
and the nuclei of the third, fourth, and sixth nerves (Mingazzini).

The inferior peduncles (crura ad medullam) issue from the white matter of
the lateral hemispheres, between the other two, and pass forwards immediately
outside the superior peduncles to reach the lateral wall of the fourth ventricle.
Here they turn sharply downwards, at a right angle, and become the restiform
bodies of the medulla oblongata.

The restiform body consists of several sets of fibres having a distinct
origin, and obtaining their medullary sheath at different periods of development.
These fibres are as follows : — (1) Fibres of small size derived from the contra-
lateral lower olives. These, which are the last to become medullated, are seen
passing as arched fibres through the corresponding half of the medulla oblongata
and across the raphe to enter the hilum of the opposite olivary nucleus. After
passing through the band of grey matter, whether joining its cells or not is not
certainly known, these fibres appear to pass longitudinally upwards in the reticular
formation of the medulla oblongata and pons, and in the tegmentum of the cerebral
peduncle, and thus to reach the cerebral hemisphere without again crossing :
ultimately they are in' all probability connected with the cerebral cortex (? of the
psychomotor region only). The existence of this connection may probably explain
those cases in which atrophy of one of the cerebral hemispheres, especially of the
psychomotor region, has been found associated with atrophy of the inferior olive of
the same side and of the restiform body and cerebellar hemisphere of the opposite side.

(2) Fibres which emerge from the adjacent cuneate nucleus (especially its outer
portion), and perhaps also from the gracile nucleus, and pass directly into the resti-
form body of the same side. These fibres may represent a bulbar ascending
cerebellar tract homologous with the dorso-lateral cerebellar tract of Flechsig which
is seen in the spinal cord, in which case the outer cuneate nucleus may very probably
represent Clarke's cell-column of the cord.

According to some authorities, the restiform body also receives a contribution through
the arched fibres from the contra -lateral nucleus gracilis and nucleus cuneatus.

(3) Fibres of the dorso-lateral ascending cerebellar tract of Flechsig, which are
traceable along the whole length of the cord from the lumbar region upwards, and
which pass into the restiform body, and through this mainly into the same side of
the worm.

(4) Fibres of the descending cerebellar tract (see p. 25) which, after removal
of the cerebellar hemisphere, undergo degeneration down the whole length of the
antero-lateral column of the cord near its periphery (see p. 32, and fig. 71, A, B, C).

(5) Fibres which are passing to or are derived from the root of the auditory nerve
and perhaps others to or from some of the other cranial nerves (see p. 93).

MICROSCOPIC STRUCTURE OF THE LAMINA.1

Each lamina of the cerebellum has a central part or core of white substance
which is an offshoot (secondary or tertiary) from the white centre of the organ,

1 Our knowledge of the actual relationship of cells and nerve-fibres in the cerebellar cortex has been
only quite recently entirely remodelled, owing to the introduction of the method invented by Golgi, and
its fruitful application firstly by Golgi himself and subsequently by Ramon y Cajal.

MICROSCOPIC STRUCTURE OF THE LAMINAE.

87

and a cortex of grey matter consisting of two layers, an inner and outer, the latter
being covered superficially by pia mater. Between the inner and outer layers of
grey matter is an incomplete stratum of large nerve-cells, the corpuscles of Purkinje.
The fibres of the white matter are medullated, and are disposed in bundles which
have a parallel course as they pass from the principal offshoots of the white centre

Fig. 63. — SECTION OP CORTEX OF CEREBELLUM.
(Sankey. )

a, pia mater ; b, external layer ; c, layer of
corpuscles of Purkinje ; d, inner or granule
layer ; e, medullary centre.

of the organ into the secondary laminae.
This parallelism is maintained in their
passage through the centre of the
laminae, but the fibres gradually turn
off obliquely into the grey matter, so
that the white core gradually thins off
towards the extremities of the laminae.
Owing to the turning outwards and
passage into the grey matter of these
bundles of white fibres, the white core
is not sharply marked off under the
microscope from the grey cortex • but
it is more distinctly marked off at the
bottom of the fissures which separate
the laminas than in the laminae them-
" selves. As the fibres pass radially into
the grey- matter they lose their parallel
arrangement, and tend to branch
amongst the small nerve -cells of the
adjacent inner layer of the grey matter ;
many pass through this and end in the
axis-cylinder processes of the cells of
Purkinje, whilst others pass beyond
these cells into the outer or " mole-
cular " layer of the grey matter.

The grey matter of the cerebellar
cortex is disposed, as already intimated,

in two distinct layers. The inner or granule layer is so called because it contains
numerous small nerve-cells known as " granules : " this layer has a reddish or
yellowish-brown colour in the fresh condition, hence it is sometimes termed the
" rust-coloured " layer. The granules are more closely packed in the outer part of
the layer ; near the medullary centre of the lamina they are separated by the
entering bundles of white fibres, between which they may penetrate for some distance
within the white centre. Besides small nerve-cells the granule-layer includes a few
glia-cells. The outer or molecular layer has, under the microscope, a finely punctated
(molecular) appearance. It is of fairly uniform thickness, whereas the granule-layer
is thicker near the extremities of the laminae than in the furrows. It contains
nerve-cells, but they are neither so numerous nor so small as the " granules " of the
inner layer, many nerve-fibres, mostly running parallel to the surface, and also a
number of fibres which run vertically to the surface (Bergmann's fibres), and end
below the pia mater. These fibres are derived from cells which are situated in the
granule-layer, and which are usually regarded as glia-cells (see p. 92).

88

THE CEREBELLUM.

The molecular layer is further in large part occupied by the dendritic proto-
plasmic processes of the large nerve-cells which lie at the junction of the granule
and medullary layers, already mentioned as the cells or corpuscles of PurTcinje. These
are conspicuous flask-shaped cells, each with a number of ramified protoplasmic pro-
cesses directed peripherally, and an axis-cylinder or nerve-process which passes
centrally into the granule-layer, where it becomes medullated, and passes directly
into a nerve-fibre of the medullary centre. As with the axis-cylinder processes of

Fig. 64. — SECTIONS OF CORTEX CEREBELLI STAINED BY GOLGI'S METHOD. (Kam6n y Cajal.)

• I. — Section taken across the lamina.

II. — Section made in the direction of the lamina.

A, outer or molecular layer ; B, inner or granule layer ; C, medullary centre.

a, corpuscle of Purkinje ; b, small granules of inner layer ; c, a protoplasmic process of a granule ;
d, nerve-fibre process of a granule passing into the molecular layer, where it bifurcates and becomes a
longitudinal fibre (in I. these longitudinal fibres are cut across and appear as dots) ; e, bifurcation of
another fibre ; g, a granule lying in the white centre.

the cells of the cerebral cortex, and, according to Golgi, with those of the anterior
horn-cells of the spinal cord, these axis-cylinder processes of Purkinje's cells also
give off lateral ramuscles (collaterals) which lose themselves amongst the granules,
some turning backwards to enter the molecular layer (figs. 69, 70). The protoplasmic
processes of the cells of Purkinje are spread out in planes which run transversely to
the laminae (Stilling), so that they are seen in their full extent only in sections
cut vertically to the surface but across the laminae (fig. 64, I.) ; whereas in vertical
sections taken parallel to the laminae, the ramifications appear limited to a com-
paratively narrowed tract (fig. 64, II.). The protoplasmic processes (dendrites) may
arise by a single root or by two roots ; in either case there is a frequent dichotomous
division, with slight enlargements at the points of division, and also the giving off
laterally of numerous ramuscles which take a more horizontal course in the mole-
cular layer than do the principal branches. The branches do not anastomose nor

MICROSCOPIC STRUCTURE OF THE LAMINAE.

89

join with those of other cells, but have free terminations, often curling back for a
short distance before ultimately ending.

Besides these dendritic processes of Purkinje's cells, the molecular layer con-
tains great numbers of very fine horizontal fibres, running longitudinally as regards
the laminae. These pass into the molecular layer from the small cells of the granule
layer. The axis-cylinder processes of the small " granules " in fact pass vertically
between the corpuscles of Purkinje and enter the molecular layer, where they join,
by a T- or Y-shaped junction, with one of the horizontal fibres just mentioned
(fig. 64, II.) ; these fibres may therefore be regarded as the branches of the axis-
cylinder processes of the granule-cells. They appear to end after a short course
either simply or by slightly ramifying. They are probably not medullated.

The nerve-cells of the molecular layer are divisible, according to their relative
position in the layer, into two kinds, outer and inner. The outer cells, i.e., those

Fig. 65. — CELLS OP THE MOLECULAR LAYER OF THE CEREBELLUM. (Ram6n y Cajal. )

a, a cell from the outer part of the layer with a horizontally directed branched axis-cylinder process ;
6, nerve-fibre processes of cells which send processes c to aid in forming the basket-work d e around the
cells of Purkinje ; /, a process directed towards the surface of the lamina.

in the outer half or so of the layer, somewhat smaller than the inner, have extensive
protoplasmic processes and an axis-cylinder process which extends for some distance
horizontally or obliquely in the layer, ramifying freely (fig. 65, a); its mode of ending
is somewhat doubtful. The inner cells, called also " basket "-cells, usually lie near the
cells of Purkinje, but they may be placed some little distance within the molecular
layer. Their protoplasmic processes pass in all directions, some of them even
reaching the surface of the organ ; the axis-cylinder process, which seems not to be
provided with a medullary sheath, usually emerges from the side of the cell and
extends laterally for some distance, giving off at intervals, as it passes along, a,
number of vertical branches which pass inwards towards the cell-bodies of Purkinje's
corpuscles, near which they become considerably enlarged (fig. 65, •&, c). Having

90

THE CEREBELLUM.

reached these they break up into a close feltwork of filaments (terminal ramification)
which surrounds the corpuscles of Purkinje, and with similar ramifications from
other cells, envelopes the corpuscle in a sort of basket-work of nerve-filaments.
This basket-work extends even for a short distance along the axis-cylinder process
of the corpuscle (fig. 66).

The " granules " of the inner, or rust-coloured, layer of the grey matter are
mostly small nerve-cells, nearly spherical, and provided with several small proto-
plasmic processes, which soon end in close bunch-like terminal ramifications within
the layer (fig. 64, V). But the axis-cylinder process is of far greater extent, and
taking a peripheral course, passes vertically beyond the corpuscles of Purkinje for

Fig. 66. — BASKET-WORK OP FIBRES AROUND TWO CELLS OF
PURKINJE. (Ramon y Cajal.)

a, axis-cylinder or nerve-fibre process of one of the corpuscles
of Purkinje ; b, fibres prolonged over the beginning of the axis-
cylinder process ; c, branches of the nerve-fibre processes of
cells of the molecular layer, felted together around the bodies
of the corpuscles of Purkinje.

a variable distance into the molecular layer, where
it becomes connected with the horizontal fibres of
that layer (fig. 64, e) in the manner before described.
A few of the " granules " are larger ; their cell-
bodies lie chiefly in the outer part of the granule-
layer, near the cells of Purkinje. They are somewhat
stellate, and have long, ramified, protoplasmic pro-
cesses ; these may penetrate both into the white

centre of the lamina, and into the molecular layer. Their axis-cylinder processes
are singularly branched, losing themselves in a ramification which may extend

Fig. 67. — TRANSVERSE SECTION OF A CEREBELLAR LAMELLA OF THE ADULT RAT SHOWING THE FIBRES

WHICH PASS FROM THE WHITE CENTRE TO THE GREY MATTER. (Ramon y Cajal. )

A, molecular layer ; B, cells of Purkinje ; C, granule-layer ; D, white substance.
«» e» /> ff, fibres which end in plexuses enveloping the principal protoplasmic processes of the cells
of Purkinje ; 6, an enveloping plexus ; c, body of cell of Purkinje ; m, "moss '' fibres.

throughout the whole thickness of the granule-layer ; it is not certainly known if
they are medullated, nor if they are connected with fibres of the white centre.

MICKOSCOPIC STRUCTURE OF THE LAMINAE.

91

Of the fibres which pass from the white centre into the grey matter of the
laminas some, which have already been described, are the nerve-processes of the cells
of Purkinje. But others are derived from the medullated fibres of the white centre,
which appear to have two modes of termination in the grey matter. Some of these
white fibres traverse the granule-layer, and, branching within that layer, exhibit
peculiar moss-like appendages, both on their ramuscles and at the place whence these
come off ; they have on this account been termed by Eamon y Cajal the " moss-
fibres " (fig. 67, m). Each such fibre, with its ramifications, extends over a con-
siderable area of the granule-layer, but the
branching and moss-like efflorescences are
especially well marked near the level of the
cells of Purkinje, beyond which they pass
into the molecular layer, where they appear
to become longitudinal and horizontal, whilst
breaking up yet again into fresh branches.

Fig. 68. — SECTION OP CEREBELLAR LAMINA OF A 15-DAY KITTEN, SHOWING SOME OF THE NKUROGLIA
ELEMENTS. GOLGI'S METHOD. (Ram6n y Cajal. )

a, pia mater ; b, processes of the neuroglia-cells passing towards the surface where they end in
conical enlargements ; c, e, elongated neuroglia-cells ; d, stellate neuroglia-cell.

Fig. 69. — Two CELLS OF PURKINJE FROM THE CEREBELLUM OF A NEW-BORN PUPPY, SHOWN BY GOLGI'S

METHOD. (Ramon y Cajal. )

A, cuticular layer of cerebellum with insertion of radial fibres.

B, layer of superficial granules.

C, molecular layer showing the longitudinal fibres derived from the granules of the next layer D
cut across and appearing as points.

D, granule-layer.

a, bodies of Purkinje's cells, the protoplasmic processes of which are still short and very irregular.

b, nerve-fibre process of one of the cells ; c, d, two collaterals from the same fibre ; e, e, their
terminal arborisations in the molecular layer.

The second kind of fibre from the medullary centre (fig. 67, a, e,f,g, fig. 70,.;', n, 0, s),
has been described by the same observer as passing towards the cells of Purkinje,
and enveloping their principal dendrites in a terminal ramification, or close plexus,
in the same manner that the bodies or bases of the cells and the commencement of
their axis-cylinder processes are enveloped in " baskets," formed, as we have seen
(p. 89), by the vertical branches of the nerve-processes of the inner cells of the

92 THE CEREBELLUM.

molecular layer. The cell-origin of the fibres which pass from the white centre
into the grey cortex is entirely unknown, but in many cases it is probably situated
in the spinal cord (see diagram, fig. 20, p. 23).

Neuroglia-cells. — Lying amongst the nerve-cells of the granule-layer which are
nearest the cells of Purkinje, are a number of relatively large cells (fig. 68) giving
off dendritic processes which are directed towards the periphery, and which course
through the molecular layer as the fibres of Bergmann before mentioned. From the
other side of these cells other processes pass off and become lost, partly amongst the
granules, partly amongst the fibres of the white centre. These centrally-directed
fibres somewhat resemble the axis-cylinder processes of nerve-cells, but the cells in
question are usually regarded as glia-cells, belonging, therefore, to the supporting

Fig. 70. — TRANSVERSE SECTION OF THE CEREBELLUM OF A 16-DAY OLD PUPPY, GOLGI'S METHOD.

(Ram6n y Cajal.)

A, epithelium-like layer of superficial zone ; B, layer of horizontal bipolar cells ; C, molecular
layer ; D, granule-layer.

a, epithelium-like cell ; b, bipolar horizontal cell ; c, cell sending a process downwards into the
molecular layer ; e, f, g, bipolar vertical cells ; h, cell of Purkinje ; i, its nerve-fibre process giving off
a collateral towards the molecular layer ; j, n, o, s, fibres from the white substance passing to form
plexuses (I, m) which envelop the upper part of the bodies and the proximal part of the dendrites of
cells of Purkinje ; r, "moss" fibre.

tissue of the nerve-centre. The peripherally-directed fibres expand at the surface of
the organ immediately underneath the pia mater into small conical enlargements,
with their bases directed superficially ; here they form a sort of limiting membrane
similar to the internal limiting membrane of the retina, which is formed by the
fibres of Miiller. Although many of the neuroglia- cells have this arrangement,
others, which are stellate in form, lie more deeply amongst the granules, or amongst
the nerve-fibres of the medullary centre.

In the embryonic cerebellum and in most animals for a few days after birth, there is a
layer of granule-like cells, several deep, superficial to the molecular layer. This has been
termed by B,am6n y Cajal, the zone of superficial granules, and he has shown that it is formed
at a certain stage of development of two distinct strata, one the more superficial composed
of epithelium-like elements set perpendicularly to the surface, and the other next to the
molecular layer composed of bipolar cells placed parallel to the surface, and to the direction

DEGENERATIONS FOLLOWING CEEEBELLAR LESIONS. 93

of the cerebellar lamellae (fig. 70, A, B). But the further development of these cells has not as
yet been ascertained, and it can only be conjectured that they become gradually transformed into
cells of the molecular layer, for no such superficial zone can be seen in the adult cerebellum.
At early stages of development there are also to be seen in the molecular layer, bipolar cells
placed with their axes vertical, and having protoplasmic processes extending down towards or
into the rust-coloured layer, and axis-cylinder processes extending towards the surface, and
becoming continued by T-shaped junctions into fibres running parallel with the processes of
the horizontal bipolar cells which have just been described. These vertical bipolar cells may
perhaps be derived from the horizontal ones, and represent a stage in the formation of the
smaller granules of the rust-coloured layer, but we have no clear evidence as to their further
course of development. Like the superficial granules they also are only found in young
animals. The cells of Purkinje in the cerebellum of embryonic and very young animals are
very irregular multipolar cells, with relatively short protoplasmic processes, but a well-
developed axis-cylinder process, which already has two or three collateral fibres extending
towards and ramifying in the deeper part of the molecular layer (fig. 69). It is not until two or
three weeks after birth (in the dog) that the dendrites begin to assume the characteristic form
and arrangement. The arborescence which in the adult cerebellum envelopes the principal
dendrites of the cells of Purkinje (see p. 91 and fig. 67), is at this early stage chiefly con-
fined to the upper part of the body of the cell (fig. 70).

DEGENERATIONS FOLLOWING CEEEBELLAR LESIONS.

The degenerations of nerve-fibres which follow lesions of the cerebellum have
been investigated by Marchi in animals (dogs and monkeys) operated upon by Luciani.

Hemiextirpation (see fig. 71). — After removal of one half of the organ
extensive degeneration is seen in all three peduncles of the same side ; very little, if
any, in the peduncles of the opposite side. It may therefore be inferred that none
of the peduncles contain commissural fibres connecting the two halves of the organ.

The degenerated fibres in the superior peduncle pass partly to the tegmental nucleus
of the opposite side, and partly to that of the same side ; in other words, the decus-
sation of these peduncles in the region of the inferior corpora quadrigemina is not
complete. Some fibres can be traced as far as the optic thalamus.

The middle peduncle, after removal of the corresponding half of the cerebellum,
is completely degenerated as far as the raphe. Degenerated fibres are seen inter-
mingled with the pyramidal fibres both of the same side and of the opposite side,
and with the fibres of the fillet and posterior longitudinal bundle, mainly of the
same side. Degeneration and atrophy are also produced in the grey matter of the
pons (nuclei pontis) of the same side. The degeneration in the fillet and posterior
longitudinal bundle is most marked on the side of the lesion ; it can be followed
upwards to the region of the corpora quadrigemina, and downwards to a tract at the
periphery of the antero-lateral column of the spinal cord. A bundle of degenerated
fibres is also seen passing to the pyramidal tract. These appear to pass upwards
towards the corpora quadrigemina, and probably to the corpus striatum, chiefly
of the same side ; a few are traceable downwards into the cord.

The inferior peduncle, after hemiextirpation of the cerebellum, is notably
degenerated in its inner and outer parts. A small degenerated bundle is traceable
with the inner arched fibres, across the raphe to the opposite lower olive which
undergoes complete atrophy ; other arched bundles pass from the restiform body to
the tract of the fillet, and of the posterior longitudinal bundle of the same side ;
and from these, as above stated, many degenerated fibres are traceable down the
periphery of the antero-lateral column of the cord, some down the pyramidal tract,
but most are situated ventral to the direct cerebellar tract of Flechsig in the
antero-lateral descending cerebellar tract.

It is also stated by Marchi that after hemiextirpation of the cerebellum, degene-
rated fibres are seen passing along with the roots of nearly all the cranial nerves,
especially the second, third, fifth (ascending root), sixth, seventh, and twelfth, and

94 THE CEREBELLUM.

the stride medullares, and along with the anterior roots of the spinal nerves. These
degenerated fibres are numerous on the same side as the lesion, but a few occur in
the opposite nerves. Those which pass to the cranial nerves run along the posterior

Fig. 71. — OUTLINE OF SECTIONS SHOWING THE DEGENERATIONS FOLLOWING EXTIRPATION OF THE LEFT

HALF OF THE CEREBELLUM IN THE DOG. (March!.)

A, lumbar cord ; B, cervical cord ; C, medulla oblongata ; D, pons Varolii ; E, mid-brain at nucleus
of third nerve.

In A and B, the degeneration is in the antero-lateral column of the same side as the lesion, except in
B, where there is a little degeneration on the opposite side.

In C, a indicates the restiform body ; 6, the ascending root of the fifth ; c, the posterior longitudinal
bundle ; d, the antero-lateral tract ; e, the pyramids ; /, the olivary nucleus ; g, the fillet ; h, the
hypoglossal nucleus.

In D, a is the superior cerebellar peduncle ; b, the middle peduncle ; c, the posterior longitudinal
bundle ; d, the fillet ; e, the antero-lateral tract ; /, the raphe.

In E, a is the nucleus tegmenti (most degeneration in the crossed superior cerebellar peduncle) ;
b. the issuing fibres of the third nerve ; d, the posterior longitudinal bundle ; e, the crusta ; /, part of
the fillet.

longitudinal bundle, those which pass to the spinal nerves down the descending
antero-lateral tract of the cord.

Extirpation of worm. — After hemi-extirpation of the middle lobe only
of the cerebellum the degeneration in the superior peduncle is comparatively
slight, and entirely crosses at the decussation to pass to the tegmental nucleus of
the opposite side. The degeneration of the middle peduncle is most marked
in the upper third of the pons ; but little occurring in the lower two-thirds.

RECENT LITERATURE OF THE CEREBELLUM. 95

That of the inferior peduncle is limited to the outer or lateral part of the restiform
body. A few fibres pass from this across the raphe to the lower olive of the
opposite side. Others pass as arched fibres to the tract of the fillet, to the posterior
longitudinal bundle, and through this to the cranial nerve-roots, especially the
third, fifth, eighth, and twelfth. Others are traceable down the antero-lateral
columns of the cord, but those to the pyramidal tract are lacking.

RECENT LITERATURE OF THE CEREBELLUMS

Bechterew, W., Zur Anatomic der Schenkel des Kleinhirns, insbesondere der Briickenarme.
Neurolog. Centralbl., 1885 ; Ueber die BestandtheUe des vorderen Kleinhirnstiels, Neurolog. Centralbl. ,
1887, and Arch. f. Anat. u. Phys., Anat. Abth., 1888.

Beevor, Ch. E., Die Kleinhimrinde, Arch. f. Anat. u. Physiol., 1883.

Bellonci, GK e Stefani, A., Contribuzione all' istogenesi della corteccia cerebellare, Memoria
letta all' Accademia de Feirara. 1886 : Archives italiennes de biologic, t. xi, 1889.

Borg-herini. Contribution a Vhistologie normale du cervelet, Archives ital. de biol., xii, 1889.

Brosset, J., Contribution a I'etude des connexions du cervelet, These, Lyon, 1890.

Cramer, A., Einseitige Kleinhirnatrophie, &c., nebst einem Beitrag z. Anatomic der Kleinhirn-
stiele, Beitrage zur pathol. Anatomic, Bd. xi., 1891.

Fusari, Sull' origine delle fibre nervose nello strata molecolare dette circonvoluzioni cerebellari dell'
uomo, Atti della R. accad. delle scienze di Torino, 1883.

v. Gehuchten, A., La structure des centres nerveux, La Cellule, t. vii, 1891.

Golgi, C., JRecherches sur Vhistologie des centres nerveux, Arch. ital. de biologic, t. iii. et iv. , 1882.

v. G-udden, P., Ueber d. Verbindungsbahnen des Kleinhirns, Berichte d. deutsch. Naturf.-Versamm-
lung, 1882 (Neurol. Centralbl.).

v. Kolliker, A., Das Kleinhirn, Zeitschr. f. wissensch. Zoologie, Bd. 49, 1890.

Luciani, L., II cervettetto, Firenze, 1891.

Marchi, V., Des degenerations consecutives d F extirpation totale et partielle du cervelet,
Archives italiennes de biologic, t. vii, 1886.

Mendel, E., Secundare Degeneration im Bindearm, Neurol. Centralbl., 1882.

Ming-azzini, G., Intorno al decorso d. fibre appart. al peduncvlus medius cerebclli ed al corpus
restiforme, Arch. p. 1. scienze mediche, 1890.
, Obersteiner, H., Der feinere Bau der Kleinhirnrinde, Biol/ Centralbl., Bd. iii., 1885.

Ramon y Cajal, S., Sobre las fibras nermosas de la capa molecular del cerebelo, Revista
trimestrial de histologia normal y patologica, 1888 and 1889 ; Sur Uorigine et la direction des pro-
longations nerveuses de la couche moleculaire du cervelet, Internationale Monatsschr. f. Aiiat. u.
Phys. , Bd. vi, ] 889 ; Sur les fibres nerveuses de la couche granuleuse du cervelet et sur I' evolution des
dements cerebelleux, Ibid., Bd. vii, 1890 ; Apropos de certains elements bipolaires du cervelet avec
quelques details nouveaux sur Involution des fibres cerebelleuses, Ibid., vol. vii, 1890.

Retzius, G., Die nervosen Memente der Kleinhirnrinde, Biol. Untersuch. Neue Folge, iii., 1892.

: See also Literature of Medulla Oblongata and Pons Varolii.

MESENCEPHALON.

MID-BRAIN, OR MESENCEPHALON, AND REGION OF THIRD
VENTRICLE, OR THALAMENCEPHALON (INTER-BRAIN).

The parts of the brain next to be described are entirely covered by the cerebral
hemispheres. They comprise the crura cerebri and corpora quadrigemina, the optic
thalami with the middle commissure, and the pineal body, in addition to the
following structures which are seen when the brain is removed from the skull and
its under-surface or base is examined, viz. : — the posterior perforated space, the
corpora albicantia, the tuber cinereum with the infundibulum and pituitary body,
the optic tracts and chiasma, and the lamina cinerea. Of these the corpora quadri-
gemina and crura cerebri are found in connection with the aqueduct of Sylvius, and
belong to the mid-brain, while the optic thalami and the other structures above
enumerated occur in connection with the third ventricle, and belong to the inter-
brain.

The aqueduct of Sylvius (iter a tertio ad quartum ventriculum) is a narrow
passage into which the upper end of the fourth ventricle gradually narrows, and
which in front expands abruptly into the third ventricle. It is rather more than

AV.

Fig. 72. — SECTIONS THROUGH THE ORIGIN OF THE FOURTH NERVE (Stilling). \

A, transverse section at the place of emergence of the nerve-fibres. B, oblique section carried along
the course of the bundles from the nucleus of origin to the place of emergence. Aq, Sylvian aqueduct,
with its surrounding grey matter ; IV, the nerve-bundles emerging ; IV, decussation of the nerves of
the two sides ; IV", a round bundle passing downwards by the side of the aqueduct to emerge a little
lower down; n.IV, nucleus of the fourth nerve. I, fillet; s. c. p., superior cerebellar peduncle;
d. V., descending root of the fifth nerve ; pi, posterior longitudinal bundle ; r, raphe.

half an inch long. In shape it varies in different parts, being T-shaped in section
below (near the fourth ventricle), triangular above (near the third), and in the
intermediate part of an elongated oval form, but somewhat shield-shaped in the
region of the superior corpora quadrigemina. It is lined by ciliated columnar
epithelium, outside which is a thick layer of grey matter, continuous with that of
the fourth ventricle. Outside this central grey matter of the aqueduct, the lateral
and ventral parts (basal part) of the mesencephalon are composed of the thick
masses of the cerebral peduncles (crura cerebri), whilst the dorsum is formed by the
lamina quadrigemina, so called from bearing the four marnillated tubercles known as
the corpora quadrigemina.

The epithelium which lines the Sylvian aqueduct is ciliated (as elsewhere in the
ventricles of the brain) and the attached ends of the cells extend as radiating
ependymal fibres through the thickness of the mid-brain to reach the surface — at
least, this can be seen to be so in the embryo and in small vertebrates, and is
probably also true for all. But some of the ependymal fibres are attached to
neuroglia cells which occur at various levels in the course of the fibres ; they have

THIRD VENTRICLE.

97

probably been formed by the detachment of some of the epithelium cells. The fibres
which extend from them often branch dichotomously besides possessing many small
lateral offsets.

The Sylvian aqueduct expands suddenly immediately after passing beneath
the posterior commissure into a comparatively large, laterally compressed cavity,
termed the third ventricle (fig. 73). This, which is deeper in front than behind,
passes at its anterior and lower extremity to a conical termination which lies over the

Fig. 73. VlEW FROM ABOVE OP THE

THIRD VENTRICLE AND A PART OP
THE LATERAL VENTRICLES (Ilenle).

The brain has been sliced horizontally
immediately below the corpus callosum,
and the fornix and velum interpositum
have been removed.

Tho, thalamus options ; Ts, its ante-
rior tubercle; Pe, pulvinar ; Com, middle
commissure stretching between the two
optic thalami across the middle of the
third ventricle ; Cf, columns of the fornix;
Cn, pineal gland projecting downwards
and backwards between the superior cor-
pora quadrigemina ; St, stria terminalis ;
Cs, nucleus caudatus of the corpus stria-
turn ; Vsl, ventricle of the septum luci-
durn ; Ccl2, section of the genu of the
corpus callosum ; Pen, commencement of
the pineal stria or peduncle, Tfo ; Cop,
posterior commissure.

optic commissure (optic recess).
Below and behind this is a conical
-depression, the mfundibulum,
leading towards \h& pituitary bod)/
(hypophysis cerebri). At the
posterior extremity, immediately
above the entrance of the aque-
duct, and separated from it by
the posterior commissure, is an-
other smaller depression (pineal
recess) (fig. 90, p. 126) extend-
ing into the stalk of the pineal
gland or conarium (fig. 73, Cn),
which here projects backwards
over the mid-brain. Another
depression extends backwards

over the pineal stalk ; this is termed the suprapineal recess (fig. 90). The
ventricle is bounded laterally by the optic thalami (fig. 73, Tho), which come
almost in contact with one another in the median plane ; and a little in advance
of the middle of the ventricle, are actually united by a connecting band of grey
matter of variable extent, termed the middle or soft commissure (fig. 73, Com. ;
fig. 83, m.c.). This is sometimes double and occasionally wanting : it is liable
to be torn across in removing the brain. The lateral walls of the cavity are
slightly convex, and each is marked towards the anterior end by a white curved
band, with its convexity forwards, which becomes more prominent as it passes
upwards towards the roof. These bands are named the anterior pillars or columns
of the fornix (fig. 73, Cf). Immediately behind the most prominent part of
each of these, between it and the anterior part of the thalamus, is an aperture
(foramen of Monro) leading into the ventricle of the hemisphere (lateral ventricle.)
VOL. in. n

98 MESENCEPHALON.

All along the upper curved margin of the lateral wall, from the pillar of the fornix
to the pineal gland, runs' a white stria, known as the stria pinealis, stria meduUaris,
or tmnia fornicis (fig. 73, Tfo). The floor of the ventricle is formed posteriorly by
the iegmenia of the crura cerebri, and where the crura diverge from one another by
the following parts, which have been already mentioned as seen at the base of the
cerebrum ; viz., commencing from behind, the grey matter of the posterior perforated
space, the corpora albicantia, sen mamillaria, the tuber cinereum and infundibnlum ;
the lamina cinerea serves to close the ventricle in front. The roof of the cavity is
limited before and behind by two commissures, named from their position, anterior
and posterior. Of these the anterior will be described with the cerebral hemispheres.

The third ventricle is lined, like the other cavities already described, by ciliated
epithelium, which is thin and flattened over the roof, i.e., lining the velum and
choroid plexuses, but longer and more columnar at the bottom and sides. The
floor, which is narrow, is formed, underneath the epithelium, of grey matter con-
tinuous with that of the Sylviau aqueduct, and this central grey matter extends a
short distance upwards on the wall of the thalamus. The central grey substance
rests behind upon the still conjoined part of the tegmenta ; but anteriorly, after
these have diverged, it comes to the surface at the base of the brain as the posterior
perforated lamina and the tuber cinereum. The lateral walls of the ventricle have
but a thin covering of neuroglia (ependyma) underneath the lining epithelium ; so
that the white covering (stratum zonale) of the thalami comes to view through it.

The epithelial covering of the roof of the ventricle is not free but covers the
under surface of the median portion of an expansion of pia mater named the velum
interposilum, which overlies the third ventricle as well as the larger part of the optic
thalami. The epithelium follows all the inequalities of two fringed vascular tracts
(choroid plwnises of the third ventricle) which project downward from the mem-
brane, and it becomes torn away when the pia mater is removed. At the pineal stria
(fig. 73, Tfo) on either side it is continuous with the epithelium covering the lateral
wall. This stria therefore represents the limit of the third ventricle so far as the
lateral boundaries of the roof are concerned : the upper surface of each optic thala-
mus is excluded from this cavity.

The central grey matter of the aqueduct (fig. 76, c. gr.) is a layer 2 to 3 milli-
meters thick which surrounds the aqueduct, and is prolonged from the grey matter
of the fourth ventricle. It contains, scattered through its substance, nerve-cells of
varying size, the largest being prolonged upwards from the locus cceruleus of the
fourth ventricle ; the cells are very numerous and small at the dorsal side of the
aqueduct. In addition to these scattered cells the grey matter of the aqueduct
contains certain more defined groups or columns of cells which are connected with
the roots of the third and fourth, and of the fifth cranial nerves. Amongst the
cells there is a network of fine medullated nerve fibres, whilst near the aqueduct
and immediately under the ependymal layer many fine longitudinal fibres are seen.

The nuclei of the third and fourth nerves (fig. 76, n.IIL, IV. extend on
either side along almost the whole length of the ventral part of the aqueduct,
close to the middle line, the nuclei of the two sides being only separated from one
another by the raphe ; at one part they even meet across this (fig. 78, n.III}.
The cells of these nuclei are large • and irregular in shape, and of a yellowish
colour. The nucleus from which the root-bundles of the fourth nerve spring
does not begin to show itself until the level of the upper part of the inferior
corpora quadrigemina, and it here lies just below and rather to the side of that
from which the bundles of the third originate. From here the bundles of the fourth
pass obliquely downwards towards the pons, and just before reaching this the nerve
turns sharply dorsal-wards, and passes into the superior medullary velum, in which
it crosses horizontally, decussating with that of the opposite side (fig. 72).

OCULOMOTOR NUCLEUS.

NUCl. EDINSER- NUCL.MED.

The nucleus from which the third nerve takes origin extends upwards underneath
the superior corpora quadrigemina, ventral to the Sylvian aqueduct, and even extends
into a corresponding situation in the posterior part of the third ventricle. The
anterior (superior) part is composed of smaller cells than the other portion : it
extends forwards into the wall of the third ventricle, and from the experiments of
Hensen and Voelckers and the observations of Starr, it appears to be subdivided
into two portions, of which that which is the more mesial, and lies just above the
corpora mamillaria, is connected Avith the fibres of the third nerve to the ciliary
muscle, whilst that which is the more lateral is connected with the fibres concerned
with the contraction of the sphincter pupillge. The main part of the oculomotor
nucleus is formed by large cells, which tend to be grouped (see diagram, fig. 74).
Thus, there are two distinct groups on each side which are dorso-lateral (dorsal
nuclei), and two which are ventro-mesial (ventral nuclei). These four nuclei are
grouped around a central nucleus which lies in the middle line. Besides these,
there is an elongated nucleus of small cells which inferiorly (caudalwards)
lies in close contact with the cen-
tral nucleus but superiorly curves
outwards. This is known as the
nucleus of Edinger and Westphal,
but it is uncertain whether it gives
origin to any fibres of the third
nerve. It has not been certainly
ascertained from which of the seve-
ral groups the fibres to particular
muscles moving the globe of the eye
proceed. From the several groups
of cells which constitute the oculo-
motor nucleus the fibres of the third
nerve pass with a curved course
through the tegmentum, to emerge
at the inner margin of the crusta of
the same side ; but the fibres from
the posterior of the dorsal groups
undergo decussation. These fibres
are believed to pass to the internal
rectus of the opposite side.

NUCi. LAT. ANT
fOARKSCMEWITiCH)

NUCL.OORS.I.(AM-~,

nUCL.VENT.I. («NT.)-__

NUCL.OORS.II.C'OST)
(V.G-UDDEN)

NUCL. CEMTRALIS-'

NUCU.VENT.II.(POST.)

Fig. 74. — DIAGRAM OP THE GROUPS OF CELLS FORMING

THE NUCLEI OF THE THIRD AND FOURTH NERVES.

(Perlia.)

In a case recorded by Kahler and
Pick, in which there was paralysis of
the levator palpebrae, the rectus superior
and the obliquus inferior, a lesion was

found involving the postero-lateral bundle of the nerve-roots. The observations of Starr point
to these three muscles being innervated from the dorsal (dorso-lateral) groups, and the rectus
internus and rectus inferior from the ventral (ventro-mesial) groups, in the order here given
(from above down).

It has been shown by Duval and Laborde that the third nerve receives fibres
from the mesial part of the posterior longitudinal bundle of the opposite side
(possibly some fibres also pass to it from the posterior longitudinal bundle of the same
side). These fibres are derived mainly from the nucleus of the sixth nerve, and pass
out along with the fibres of the third nerve to the internal rectus, so that the nucleus
of the sixth thus supplies both the external rectus of the same side entirely, and the
internal rectus of the opposite side partially (fibres derived from the nucleus of the
third also going to the internal rectus). These are, it may be noted, the muscles
which are brought together into action in con^ug-ate; dbyiatioii of' the cye&tq eidBe,r

' '

100

MESENCEPHALON.

side, and the cases which are sometimes met with of conjugate paralysis involving
the internal rectus of one side, and the external rectus of the other side, which
are accompanied by atrophy of the nucleus of the sixth, are thus accounted for.

The prolongation of the tipper nucleus of the fifth nerve consists of a small
number of large globose cells (figs. 75, 76, d.V), which lie at the extreme lateral
margin of the grey matter of the aqueduct close to the bundles of the descending
root of the fifth nerve, towards which their axis-cylinder processes are directed. This
nucleus and root gradually become smaller, and disappear before the superior end of
the mesencephalon is reached.

The crura cerebri (fig. 32, P) emerge from the upper border of the pons and
diverge from one another, leaving between them the posterior perforated space and
the corpora mamillaria and disappearing in the cerebral hemispheres under the
optic tract. The triangular interval seen at the base of the brain to be enclosed
between the diverging crura has been termed trigonum inter peduncular e by
Schwalbe. Near the point of the angle of divergence the roots of the third nerve
issue in several bundles from a groove along their inner side (fig. 32, ///.) ; and
this groove serves to indicate the separation between the more prominent ventral
part of the peduncle ( pes s. basis s. crusta pedunculi, fig. 75, cr.) and the dorsal
and larger part (tegmentum, /.) which is in great measure concealed from view by

Fig. 75. — OUTLINE OF TWO SECTIONS ACROSS
THE MESENCEPHALON. Natural size.
(E. A. S.)

A, through the inferior pair of the corpora
quadrigemina : B, through the superior pair.

cr, crusta ; s.n., substantia nigra ; t, teg-
mentum ; s, Sylvian aqueduct with the cen-
tral grey matter ; e.g., grey matter of quad-
rigeminal bodies ; l.g., lateral groove ; p.L,
posterior longitudinal bundle ; d. V, descend-
ing root of fifth nerve; s.c.p., superior cerebellar peduncle ; /. fillet. The dotted circle in B indicates
the tegmental nucleus.

the pes when viewed from below and in front. A section into the crus cerebri
shows the two parts of which it is composed to be separated from one another by a
tract of dark coloured grey substance known as the substantia nigra (fig. 75, sii),
which comes to the surface on the inner side at the groove above mentioned from
which the third nerve issues (sulcus oculomotor ii), and on the outer side also along
a grooved line — the sulcus lateralis (fig. 75, l.g.}.

Of the two main parts of each peduncle the crusta (cr) is formed almost entirely
of lamellated bundles of longitudinal fibres, some of which are continuous with the
pyramid-fibres of the medulla oblongata and pons, whilst others are superadded ; and
the tegmentum is a continuation of the formatio reticularis of those parts, with the
addition of much grey matter and white fibres, amongst the latter being those of
the superior peduncle of the cerebellum. The two ventral portions (crustse or pedes)
are entirely distinct from one another (as shown in the accompanying sections,
fig. 75), and each is marked off externally from the tegmentum of the same side by
the grooves just mentioned ; but the two tegmenta are united in the median plane
by a prolongation of the raphe, and extend dorsally at the sides of the aqueduct to
become continuous with the bases of the corpora quadrigemina.

Crusta. — The crusta is semilunar in section, the substantia nigra projecting
into it with an irregular convex border. It is made up of longitudinal white fibres
which become arranged in the higher parts of the mid-brain into flattened bundles,
with their edges dorsal and ventral, separated from one another by processes of pia
mater. The main part is a direct prolongation of the longitudinal bundles of the
pops and passes superiorly towards the internal capsule of the cerebral hemisphere.

THE CRURA CEREBRI. 301

Close to the substantia nigra, the bundles of white fibres are smaller and some-
what separated by projections of the grey matter extending between them. They
have received the name of stratum intermedium. These are usually stated to have a
different origin and destination from the other fibres of the crusta, passing, accord-
ing to Meynert, between the lenticular nucleus of the corpus striatum (see p. 131),
and the substantia nigra and reticular formation of the bulb and pons. It is
doubtful, however, if this is true for any of these fibres, and is certainly not the
case with the majority, for (in monkeys) after a lesion of the Eolandic region, most
if not all the fibres of the stratum intermedium undergo degeneration along with the
fibres of the pyramidal tract, to which, therefore, they must be regarded as belonging.
The pyramidal tract of the mesencephalon, or continuation of the pyramid-
bundles of the pons, occupies about the middle third of the crusta. Superiorly
its fibres pass through the middle part of the internal capsule to the fronto-parietal
or Rolandic region of the hemisphere. By far the majority arise from the cortical
cells, but a few have their cell-origin in the cord or bulb, and degenerate after
lesions of these parts.

It is remarkable that whereas in the lower part of its course (spinal cord and
bulb) the fibres of the pyramidal tract acquire a medullary sheath later than the
other fibres of the white columns, in the upper part (crus cerebri and cerebrum) it is
acquired earlier than in the other fibres.

The outer or lateral third of the crusta is formed of fibres which are traceable
downwards to the lateral longitudinal bundles of the pous, and upwards to the
posterior part of the internal capsule, but their origin and destination have not yet
been satisfactorily made out. They are probably connected superiorly with the
occipito-temporal regions of the cerebral cortex, and according to Flechsig they arise
below from the cells of the nuclei pontis.

The mesially situated bundles of the crusta are also distinct from the pyramidal
tract proper (Flechsig), being developed at a later period. They are perhaps
connected through the anterior part of the internal capsule with the prefrontal
region of the hemisphere. Finally, one well-marked bundle in the crusta is con-
nected with the fillet (mesial fillet, pp. 66, 67, and 103). This bundle is at the
lateral border of the pyramidal tract in the upper part of the crusta, but lower down
crosses obliquely over or between the fibres of that tract to attain the mesial border
of the crusta, whence it is traceable to the fillet. It contains, according to Spitzka,
the afferent cerebral tracts of the cranial nerves. Traced upwards it is lost in the
subthalamic region.

Lastly the crusta includes some fibres derived originally from the cerebellum and
joining the pyramidal tract in its passage through the pons, such fibres being
scattered amongst the fibres of the other tracts.

The substantia nigra is a mass of grey matter which is characterised by the
presence of a number of very darkly pigmented irregular nerve-cells, which give the
substance in which they are scattered the appearance from which it derives its name.
It forms a layer which separates the crusta from the tegmentum. It is thicker
near the mesial border of the peduncle than laterally, where the tract of the fillet
may be but incompletely separated by it from the longitudinal bundles of the crusta
It commences at the upper margin of the pons, and can be traced as far forwards as
the posterior border of the corpora albicantia. At the origin of the third nerve it is
traversed in its mesial part by some of the issuing fibres of the nerve-root. The
grey matter of the substantia nigra projects here and there between the adjacent
bundles of the crusta ; one considerable projection in particular in the lower part
of the mesencephalon serving to mark off the mesial portion of the crusta from the
rest. The cells in this projection are much smaller, and relatively more numerous
than in the rest of the substantia nigra.

102

MESENCEPHALON.

The tegmentum, like the formatio reticularis of the bulb and pons, of which
it is the prolongation upwards, is composed of small longitudinal bundles of white
fibres, separated by transversely coursing or arched fibres, together with a con-
siderable amount of grey matter containing scattered nerve-cells.

In addition to these diffused bundles of longitudinal fibres there are others
which are collected into more defined tracts. One such tract constitutes the
posterior or dorsal longitudinal bundle, which is seen in all sections of this
part of the brain as a pyriform area of transversely cut fibres which lies on each side
of the middle line between the grey matter underlying the aqueduct, and the
formatio reticularis (fig. 76, p.l.l.}. The fibres which constitute this bundle below

Fig. 76. — TRANSVERSE SECTION ACROSS THE MID-BRAIN, THROUGH THE INFERIOR CORPORA QUA^RIGEMIN A.
MAGNIFIED ABOUT 3J DIAMETERS. (E. A. S.) From a Photograph.

gr. , dorsal quadrigeminal groove (sulcus longitudinalis) ; c.q.p., corpus quadrigeminum postering;
str.L, stratum lemnisci ; c.gr. , central grey matter; «.///, IV, oculo-motor nucleus; d. V, descending
root of fifth nerve ; p.l.b., posterior longitudinal bundle ; f.r.t., forrnatio reticularis tegmenti ; d, d',
decussating fibres of tegmentum ; s.c.p., decussating fibres of superior cerebellar peduncles ; /, upper
fillet; /', lower or lateral fillet ; p.p., pes pedunculi ; s.n., substantia nigra ; g.i.p., interpeduncular
grey matter ; Sy, Sylvian aqueduct.

have already been noticed (see p. 65 and figs. 53, 54) ; traced upwards its fibres
become related to the nuclei of the third and fourth nerves, and mostly pass out with
the roots of these nerves. The posterior longitudinal bundle is composed exclusively
of large nerve-fibres, which acquire their myelin at an early stage, in fact, as soon
as the roots of the nerves themselves. Although its fibres are large, it gives off
principally fine nerve-fibres (Koppen). If this is the case they are probably
collaterals. It appears to be developed in nearly all vertebrates, and in some is
better marked than in mammals ; e.g., in the lizard it can be traced right down the
cord dorsal to the anterior or ventral commissure. Although mainly related to the

TRACT OF THE FILLET. 103

sixth, fourth and third nerve-roots, fibres also pass from it to the auditory nucleus,
and others to the cerebellum. After giving off fibres to the root of the third nerve the
posterior longitudinal bundle is continued into the posterior commissure (see p. 109),
and partly upwards into the subthalamic region (? to the substantia interansalis, see
p. 112). The posterior longitudinal bundles come close together at the raphe, and
fibres pass from one to the other. These are probably the fibres which effect a crossed
connection between the abducens nucleus of the one side and the fibres passing to
the internal rectus by the third nerve of the other side (see pp. 63 and 99). Perhaps,
also, a connection is established through the posterior longitudinal bundle between
the facial and the oculomotor nucleus (Mendel). The posterior longitudinal bundle
is very small in the mole (Forel), large in reptiles and amphibia (Spitzka).

Brachium conjunctivum ; superior cerebellar peduncle. — Another tract
of longitudinal and decussating fibres is derived from the superior peduncle of
the cerebellum, which we have already traced as it passes forwards over the
superior end of the fourth ventricle. Reaching the sides of the aqueduct as a
well-marked bundle, of semilunar shape in section (fig. 72, s.c.p), it gradually takes
a more ventral position as it is traced upwards in the mesencephalon, and its
fibres soon begin to pass across the raphe, decussating with those of the other side
(fig. 75 A, and fig. 76, s.c.p.}, the decussation extending as far upwards as the superior
pair of corpora quadrigemina. Having thus crossed to the opposite side the tract
in question pursues its course longitudinally upwards, appearing at first as a white
bundle, but higher up enclosing in its passage a tract of grey matter with numerous
large piginented cells, known as the nucleus of the tegmentum or red nucleus (fig.
75, B, and fig. 78, r.n.), and probably receiving an accession of fibres from these cells.
Above, the tract passes into the ventral part of the optic thalamus. Some fibres
do not cross, but enter the red nucleus of the same side.

Between the two red nuclei a small white bundle (Meynerfs bundle) passes
backwards on either side of the raphe from the ganglion of the habenula near the
roof of the third ventricle to a small mass of grey matter which lies between the
crura (ganglion interpedunculare, fig. 76, g.i-p.).

Tract of the fillet. — The fillet, which, in sections across the upper part of the
pons, forms a considerable flattened bundle of longitudinal fibres at the ventral
border of the formatio reticularis, is traceable upwards into the ventral part of the
tegmentum. Soon, however, the large laterally situated part of this tract is seen to
pass obliquely outwards and emerge at the side of the crus cerebri, curving obliquely
over the outer side of the prolongation of the cerebellar peduncle (fig. 75, A, /),
and tending for the most part towards the inferior corpora quadrigemina. It is seen
on the surface as a band of obliquely curved fibres, occupying a triangular area at
the side of the tegmentum (fig. 76,/'), and it was to this band that the name of
fillet was originally applied by Reil. It is now known as the lower or lateral fillet.
It is reinforced by fibres from the superior medullary velum which also curve round
the superior cerebellar peduncle, and which are probably derived from the antero-
lateral ascending tract of the cord, for they undergo degeneration after section of
the cord (see below). The fillet is covered externally by a thin layer of grey matter
containing nerve-cells.

But all the fibres of the tract of the fillet do not take the course above indicated.
Those nearest the middle line (mesial fillet) separate themselves from the rest, and
pass at the lower part of the mesencephalon into the crusta (see p. 101), where they
form a mesial bundle (Wernicke), which is traceable up into the subthalamic region,
where it joins the ansa lenticularis. Those next in order (middle portion) are for
the most part, according to Forel, continued upwards in the formatio reticularis
of the tegmentum, but many of the fibres become lost amongst its cells, and
are not traceable further as a distinct tract. According to Edinger, they have a cell-

104 MESENCEPHALON.

station in a special group of nerve-cells (upper nucleus ofthefilleC) at the level of the
inferior corpora quadrigemina. Some of the lateral fibres of this middle portion,
however, pass to the upper corpora quadrigemina (upper fillet), and even extend
beyond the superior quadrigeminal region to the subthalamic region (Flechsig),
eventually reaching the parieto-occipital part of the cerebral hemispheres by the
posterior part of the internal capsule (v. Gudden). Both the upper and lower fillet
receive fibres from the antero-lateral columns of the spinal cord, for after hemisection
of the cord degenerated fibres are seen on the same side, both in the lateral fillet of the
inesencephalon, where they are mingled with the mass of undegenerated fibres which
have been derived from the nucleus gracilis and nucleus cuneatus (see p. 53 and
below), and in the bundle of the upper fillet, which enters the superior corpora quadri-
gemina ; a few degenerated fibres are also seen in corresponding positions on the oppo-
site side. Traced downwards the fibres of the lower fillet pass, as we have seen, a few
by means of the trapezium towards the auditory nucleus of the opposite side, a few
to the antero-lateral column of the medulla oblongata and cord (antero-lateral
ascending tract), but most are traceable to the anterior column of the medulla
oblongata dorsal to the pyramids, and passing across the raphe, proceed as internal
arched fibres to the nuclei of the posterior columns, from the cells of which they in
all probability arise.

To sum up : — The fillet as a whole is composed of ascending fibres, most of which
are derived from the nuclei of the opposite posterior columns of the medulla
oblongata, but a few from other sources. The fibres of the antero-lateral ascending
tract which enter the fillet may, according to Edinger, be derived from cells of the
opposite posterior horn of the spinal cord ; if so, all the fillet-fibres may be regarded
as having crossed over from the opposite side, some in the cord, others at the
superior or sensory decussation in the medulla oblongata. The fact that they are
thus derived is however by no means certain. Superiorly the fillet may be described
as being prolonged upwards above the pons in three parts, of which one — the lower
fillet — goes to the inferior of the corpora quadrigemina of the same side, a second —
upper fillet — to the superior corpora quadrigemina and occipital region of the
cerebral hemisphere, and a third, mesial fillet, to the base of the cerebrum through
the crusta.

DORSAL PAET OF THE MID-BRAIN: CORPORA QUADRIGEMINA.

As before stated the Sylvian aqueduct is covered on its dorsal aspect by the
quadrigeminal lamina, bearing the bodies of the same name. The median part of
the lamina is marked by a comparatively wide groove (sulcus longitudinalis, s.
saffittalis), shallower inferiorly, which serves to separate the corpora quadrigemina
of opposite sides (fig. 77). This grooved surface, which is raised above the level of
the upper medullary velum, is connected with the velum by a small median strand
of longitudinal fibres termed the frcenulum veli (fig. 77, fr). In front of the upper
(anterior) pair of corpora quadrigemina the groove is interrupted by a transverse
white prominence — the posterior commissure ; but both this and the upper end of
the median groove are in the natural condition concealed by the pineal body (p),
which projects backwards and downwards from the posterior wall of the third
ventricle and rests between the upper pair of quadrigeminal bodies. A well-marked
narrow transverse groove (sulcus transversus) which commences a short distance
from the middle line, and is curved round the lower border of the upper tubercle,
separates this from the lower tubercle of the same side.

The corpora quadrigemina are two pairs of rounded eminences which are
mainly composed of grey matter, although covered externally by and containing in
their interior many white fibres. The upper or anterior tubercles (_fig. 77, c.q.s.}

THE CORPORA QUADRIGEMINA.

105

c.

S.TtVV

cbl

are broader and longer and also darker in colour, but slightly less prominent than
the lower or posterior (c.q.i)1. Laterally the corpora quadrigemina are not bounded
by a distinct groove, but each appears to be prolonged obliquely upwards and forwards
into a prominent white tract, known as the brachium of the corresponding tubercle.
The lower (posterior) brachium (fig. 77, br.i.) loses itself underneath an oval
prominence which is seen at the side of the upper end of the crus cerebri, and is
termed the inner geniculate bod?/ (fig. 77, c.g.i. ; fig. 78, c.g.m.}. The upper (anterior)
brachium passes between the same geniculate body, and the prominent posterior
extremity of the optic thalamus into the external geniculate body (fig. 78, c.g.i.} and
the optic tract, of which it maybe regarded as the main prolongation (see also fig. 86,
p. 117). The continuity is much better seen externally in some animals than in man.
The connection of the superior quadrigeminal bodies with the optic tract and the
sense of sight is far more intimate than that of the inferior. For if in a young
animal the eye on the one side be extirpated, the operation is found to be followed

Fig. 77. VlEW OF THE MEDULLA, PONS, AND

MESENCEPHALON FROM THE BIGHT SIDE AND
BEHIND. (E. A. S. )

The cerebellum, the inferior medullary velum,
and the right half of the superior medullary
velum, have been cut away, so as to display the
fourth ventricle.

c.q.s, c.q.i, superior and inferior quadri-
geminal bodies of the left side ; the pineal
gland, p, is seen projecting backwards between
the superior bodies, and the frsenulum. fr,
passes up from the superior medullary velum,
s.m.v, to the interval between the posterior
quadrigeminal bodies ; th, right thalamus opti-
cus ; br.i, brachium of the inferior quadrigeminal
"body passing underneath the inner geniculate
body, c.g.i. ; /, superficial stratum of fibres of
the fillet, covering the tegmentum of the crus
cerebri ; c, crusta of the crus cerebri, separated
from the tegmentum by the lateral groove, l.g. ;
P, upper part of the pons ; III, IV, &c., the
corresponding cranial nerves. The rest of this
figure will be found described at p. 43.

after some time by atrophy of the
superior quadrigeminal body and of its
brachium, whereas the inferior quadri-
geminal body and brachium is un-
altered (Gudden). Moreover, in the
mole the inferior quadrigeminal body
is well developed, whereas the superior
is atrophied.

The lower or posterior quadri-
geminal bodies are composed almost

entirely of grey substance (the so-called nucleus of these bodies (fig. 76, c.q.p.) which
is separated by a thin layer of the fillet from the central grey matter of the aqueduct
and contains numerous small and some larger nerve-cells. The connections of these
have not yet been satisfactorily worked out, but they are believed to be closely
related to the termination of the fibres of the lower fillet. The nuclei are united
across the middle line by a commissural portion of grey matter which is bounded
superficially and deeply by transverse white fibres derived from the fillet.

1 The term nates is often applied to the superior or anterior corpora quadrigemina, and testes to the
inferior or posterior. These names were used by Vesalius, but are somewhat misleading, and have fallen
into disuse.

106

MESENCEPHALON.

The superficial fibres are continuous laterally and above with the fibres of the
brachium of ths inferior quadrigeminal body, and laterally and below with those of
the lower fillet. On the other hand, if the fibres of the lower fillet are traced down-
wards, they are partly found as we have already seen (p. 104) to be continuous with
fibres of the trapezium ; which again is connected with the principal nucleus of the
auditory nerve (cochlear division) of the opposite side (Flechsig). This would
appear to indicate a close connection between these posterior or inferior quadrigemi-
nal bodies and the auditory nerve, and in conformity with this view it is noticeable
that it is only those animals (mammals) which have a well-developed spirally wound
cochlea that show the inferior corpora quadrigemina as distinct prominences. In
nearly all vertebrates below mammals there are merely corpora bigemina, and these
seem mainly to represent the anterior pair of the quadrigemina of mammals. As

Fig. 78. — SECTION ACROSS THE MID-BUAIN, THROUGH THE SUPERIOR CORPORA QUADRIGEMINA.
Magnified about 3£ diameters. (E. A. S. ) From a Photograph.

Sy., aqueductus Sylvii ; c.p. , commissura posterior ; gl.pi., glandula pinealis ; c.q.a., grey matter of
one of the superior corpora quadrigemina ; c.g.m., corpus geniculatum mesiale ; c.g.L, corpus genicu-
latum laterale ; tr. opt., tractus options ; p.p., pes pedunculi ; p.l.b., posterior longitudinal bundle ;
fi., upper fillet ; r.n., red nucleus ; n.III, nucleus of third nerve ; ///, issuing fibres of third nerve ;
I. p.p., locus perforatus posticus.

already mentioned, this anterior pair is chiefly connected with the optic nerves and
therefore with the visual sense.

The tipper or anterior quadrigeminal bodies of man have been carefully
investigated by Tarfcuferi. Most externally or uppermost is a thin layer of superficial
neuroglia, containing no nerve-cells or fibres, but only fine stellate glia-cells and
the ends of glia-fibres which radiate from the central canal (aqueduct) towards the
periphery. Excluding this neuroglia-layer, and also the central grey matter around
the Sylvian aqueduct, Tartuferi distinguishes four strata in vertical sections.

QUADUIGEMINAL BODIES. 107

1. Stratum zonale ; superficial white layer. — This is a relatively thin stratum of
transversely coursing fine nerve-fibres, which are derived through the superior
brachiura from the optic tract and retina.1 Many of them dip down and lose
themselves in the next layer, but some appear to be continued towards the middle
line and to decussate with others from the same stratum of the opposite side.

2. Stratum cinereum ; grey cap. — A layer of grey matter, sernilunar in section,
being of considerable thickness opposite the most prominent part of the tubercle,
but thinning off at its margins. Its nerve-cells are numerous but vary in size, the
smaller ones being near the stratum zonale, the larger in the deeper part of the
layer. They mostly send their dendrites or protoplasmic processes outwards,
i.e., towards the stratum zonale, while their nerve-processes (axis-cylinder processes)
are directed inwards towards the deeper layers.

3. Stratum albo-cinereum superius ; upper grey-white layer ; stratum opticum. —
The grey matter of this layer is largely interrupted by nerve-fibres, which are
continued like those of the stratum zonale from the optic tract, which enters by the
superior brachium at the antero-lateral aspect. The fibres differ in calibre in the
different parts of the layer, and it may be subdivided accordingly into (a) a medio-
dorsal zone of coarse medullated fibres, (/3) an intermediate zone of fine medullated
fibres, and (y) a central zone containing much grey matter interspersed with bundle?
of white fibres.

These are described by Ganser as three distinct layers, and termed the third, or superficial
medullated layer, the fourth, or middle medullated, and the fifth, or middle grey layer ; while
the fourth layer of Tartuferi, immediately to be mentioned, becomes the sixth and seventh of
Ganser.

The whole stratum is richly beset with large nerve-cells, which send their axis-
cylinder processes mostly into the next or fourth stratum. Of the nerve-fibres, those
of the intermediate zone (/3) are retinal fibres according to Tartuferi ; those of the
central zone (y) are probably derived from the corona radiata of the occipital region
of the brain, whilst the coarse fibres of the medio-dorsal zone are perhaps derived
from the opposite side.

4. Stratum albo-cmereum inferius: deep grey-white layer: stratum lemnisci. —
This, although composed of grey matter, is also traversed by many nerve-fibres which
appear to be connected with the upper fillet, and probably end in the layer. Some
of the fibres, however, are derived from the large cells of the fourth layer, and others
from the nerve-cells of this stratum itself (which contains many cells of large size).
It is possible that some fibres are derived (over the aqueduct) from the fillet of
the opposite side.

Ganser subdivides this layer into two, which he terms respectively the deep white (sixth),
and the deep grey (seventh) layers.

Structure of the optic lobes of birds. — The relations of the cells and fibres have not
been very satisfactorily made out in the corpora quadrigemina of mammals, but in the optic
lobes of the bird, which correspond, as we have seen, to the anterior or superior quadrigeminal
bodies of the mammal, these relations have recently been considerably elucidated by the
investigations of Ramon y Cajal.

All who have specially worked at this subject distinguish more strata in the optic lobes of
birds than in the corresponding bodies of mammals. Thus Bellonci makes the number of
layers (exclusive of the central grey matter of the aqueduct) nine, Stieda, twelve, whilst
Cajal distinguishes as many as fourteen strata. Of these the most superficial (1.) is a layer
of thick medullated fibres coming directly through the optic tract and chiasma from the
retina of the opposite side. (In birds all the optic nerve-fibres cross at the chiasma.) They
pass in from the side (so that they are cut across in a sagittal section, fig. 79), and after a
variable course turn downwards into the deeper layers, where they end at four different levels
(as far as the seventh layer) in non-medullated terminal arborisations. Of these terminal

1 Monakow states that in the dog the anterior brachiura contains some fibres from the occipital cortex.

108

MESENCEPHALON.

ramifications, that in the seventh layer is flattened horizontally, the others are more extended
vertically (fig. 80). Some of these terminal arborisations end in a special circumscribed part
of the lobe, which is known as the ganglion of the. roof. This contains a large number of nerve-
cells, the protoplasmic processes of which interlace with the optic arborisations, whilst their
nerve-fibre processes are directed towards the deeper layers of the lobe. All the layers below
the first contain nerve-cells, as well as nerve-fibres, but the seventh is mainly composed of the

expanded ramifications of the optic fibres just men-
tioned, and of similar expansions of the superficially
directed nerve-fibre processes of cells from the tenth
layer (fig. 79, ./,./). The cells vary in size and shape
in the different layers, but on the whole they are
smallest nearer the surface and largest in the deeper
layers (tenth to thirteenth). With the exception
of the cells of the tenth layer just mentioned, the
cells send their axis-cylinder processes downwards to
pass away as nerve-fibres of the fourteenth layer,
which is chiefly formed of large medullated nerve-
fibres, although some nerve-cells are even here inter-
spersed. But some of the smaller cells of the more
superficial layers (fig. 79, d) belong to Golgi's
second type of nerve-cell, i.e., their axis-cylinder
processes do not pass into nerve-fibres, but break up
into a terminal arborisation a short distance from the
cell, and interlace amongst the cells of some of
the other layers. The third, fifth, seventh, and ninth
layers all have relatively few cells and a molecular
aspect, due apparently to the fine arborisations of the
nerve-fibre or axis- cylinder processes which they con-
tain. The protoplasmic processes of the cells are, some

Fig. 79. — ANTEKO-POSTERIOR SECTION OF THE OPTIC LOBE OF A BIRD PREPARED BY GOLGI'S METHOD

(R. y Cajal).

a, optic fibres cut across ; b, stellate cell of second layer ; c, fusiform cell of third layer ; d, cell
with axis-cylinder ending in a varicose arborisation in the eighth layer ; e. large horizontal cell of fourth
layer ; f,ff,k, globular cells of eighth layer ; t, cell with descending axis-cylinder of this layer ; j, cell
with axis-cylinder ascending to optic layer ; k, collateral arborisation of this axis-cylinder in the seventh
layer : m, large fusiform cells with recurrent axis-cylinders ; n, pyramidal cell with descending axis-
cylinder ; o, large cell of tenth layer; p,q,r, cells of the lowest layers, all with axis-cylinders directed
towards the deep layer of nerve-fibres, s.

Fig. 80. — TRANSVERSE SECTION OF OPTIC LOBE OF A BIRD, GOLGI'S METHOD (R. y Cajal).

The superficial part only is represented, as far as the seventh layer.

a, optic fibres ; b, their arborisation in the second layer ; c, that in the fourth layer ; d, that in the
fifth layer ; c, that in the seventh layer.

of them, very long, and when coursing vertically often extend as far as the layer of optic
fibres, on the one hand, and the deep medullary layer on the other. The axis-cylinder
processes sometimes come off from the dendrites. sometimes from the body of the cell. Of
the fibres which form the deepest layer, although many, as just stated, are derived from the

THE POSTERIOR COMMISSURE.

109

cells of the optic lobe, and are therefore passing away by that layer (probably to the higher
parts of the brain, on the one hand, and to the bulb and spinal cord, on the other), some have
a contrary direction and are passing -into the grey matter, where they end in extensive
ramifications extending as far towards the surface as the sixth layer.

The fibres of the deep medullary layer, on leaving- the optic lobe, partly encircle, partly
traverse, four groups of nerve-cells, which are known as the optic f/anglia. It is probable
that these may in part represent the external or lateral geniculate body of mammals. The
fibres give off collaterals, which end in ramifications amongst the cells of these ganglia ; some
of tbe fibres appear altogether to terminate in this way. On the other hand, some of the
ganglion-cells send their axis-cylinder processes to join the stream of traversing nerve-
fibres. It is not known what ultimately becomes of these processes, but from analogy
with what obtains in mammals (see diagram, p. 119), it is not improbable that they may pass
to the cortex cerebri.

The posterior commissure (fig. 73, Cop., fig. 78, c.p.\ which overlies the
upper end of the aqueduct and appears in the posterior wall of the third ventricle,
is generally described with that cavity. It appears, however, to be in part a con-

c.qr.s

Fig. 81. — SECTION THROUGH THE SUPERIOR PART OF ONE OF THE SUPERIOR CORPORA QUADRIGEMINA

AND THE ADJACENT PART OF THE OPHC THALAMUS (after Meynert).

«, aqueduct of Sylvius ; gr, grey matter of the aqueduct ; c.q.s, quadrigeminal eminence, consisting
of: I, stratum lemnisci ; o, stratum opticum ; c, stratum cinereum ; Tk, thalamus (pulvinar) ; c.g.i,
C.g.e, internal and external geniculate bodies ; br.s, br.i, superior and inferior brachia; /, upper fillet ;
p.l, posterior longitudinal bundle; r, raphe ; III, third nerve; n.III, its nucleus; l-p.p, posterior
perforated space ; s.n, substantia nigra ; above this is the tegmentum with its nucleus, the latter being
indicated by the circular area ; cr, crusta ; II, optic tract ; M, medullary centre of the hemisphere ;
n.c, nucleus caudatus ; st, stria terminalis.

tinuation of the commissural fibres of the fillet above mentioned. Its fibres,
according to Meynert, coming from the tegmental part of the mesencephalon, cross
to the other side, and after passing through the thalamus diverge into the white
substance of the cerebral hemispheres. They may in part comprise commissural
fibres between the two thalami, and some are connected with the pineal roots.
According to Darkschewitsch they are divisible into two categories. Some form a
ventral portion of the commissure, being derived from the posterior longitudinal
bundle and the nucleus of the third nerve, and pass across to the root of the pineal
body of the opposite side, while the rest, which form a dorsal portion of the com-
missure, connect the deep white layers of the superior corpora quadrigemina with
the corona radiata of the opposite side.

The geniculate bodies are intimately related to this region of the brain, the

110 THALAMENCEPHALON.

mesial (internal) with the inferior quadrigeminal bodies, the lateral (external)
with the superior quadrigeminal bodies and optic tract. The two are separated by
a part of the optic tract which sweeps round the internal geniculate body in passing
as the superior brachium, to the grey matter of the corp. quadrig. sup. (fig. 86, p. 117).
Both the geniculate bodies are continuous with the posterior part of the thalamus,
lying between this and the lateral margin of the crusta. The internal geniculate
body receives ventrally and mesially the inferior brachium, which passes forwards
to it by the side of the tegmentum from the corp. quadrig. inf., and appears to dip
under it. Some of the fibres of the optic tract appear to pass out of it on its latero-
ventral aspect, but as the internal geniculate body remains unaffected when the eye
is extirpated, and is, moreover, as well as the corp. quadrig. inf., well developed
in the mole, it is probable that this connection with the optic fibres is more apparent
than real.

The lateral or external geniculate body is, on the other hand, intimately related
to the optic tract and corp. quadrig. sup. as well as to the visual area of the
cortex cerebri (occipital region). It is of a somewhat darker colour than the
adjacent part of the thalamus with which it is intimately connected, and is formed
of several curved layers of grey matter with white lamellas of optic nerve-fibres
separating them (fig. 81, c.g.e.}

Its cells are large and pigmented, and appear chiefly to send their nerve-fibre
processes to the cortex of the occipital region, for if this region is removed on one
side in young animals the cells of the external geniculate body of the same side
undergo atrophy (Monakow.) On the other hand, if the eyes are extirpated, the
atrophy which extends along the optic tracts involves the grey matter between the
cells, but not the cells themselves. From this it is inferred that the intercellular
grey matter of these bodies is largely composed of ramifications (? of collaterals)
of the retinal fibres. The same statements apply to the adjacent part of the
optic thalamus (pulvinar) which appears intimately associated both in structure
and function with the lateral geniculate bodies.

The optic thalami (fig. 82, Tho), as seen from above after the removal of the
corpus callosum, fornix, and velum interpositum, are large oval-shaped masses of grey
substance covered dorsally by a thin stratum of white fibres. The dorsal surface is
marked by a shallow longitudinal groove, which inclines inwards as it passes forwards,
and terminates a short distance from the anterior extremity of the surface. This
anterior extremity is raised into a prominence termed the anterior tubercle (fig.
82, Ts), and together with the part of the upper surface which is placed outside
the groove, projects into the ventricle of the corresponding cerebral hemisphere
(fig. 88), and is covered by the lining epithelium of that cavity. This part of the
upper surface is limited externally by a white band, the stria terminalis ($/"), which
separates it from the part of the corpus striatum which is seen in the lateral
ventricle. The longitudinal groove above mentioned corresponds with the thickened
margin of the fornix, the edge of which extends over the surface of the thalamus
along the line of the groove. The part of the upper surface behind the groove does
not appear in either the third or the lateral ventricle, and is therefore not covered with
epithelium like the rest. It is limited internally by a sharp edge which separates
it from the mesial surface and which is marked by a white stria (taenia fornicis, fig.
82, Tfo.} leading to the pineal body. It is along this stria, which is surmounted by
a ridge-like extension of ependymal tissue that the thin epithelium which roofs in
the ventricle is attached laterally : this epithelium always comes away when the
covering of the velum interpositum is removed. At the posterior and inner
extremity of the thalamus, there is seen, as in front, a well-marked prominence
(posterior tubercle or pulvinar (/V) ) which projects over and partially conceals the
brachia of the corpora quadrigemina. Between the pulvinar and the peduncle of the

OPTIC THALAMUS.

Ill

pineal body (habenula) (Pen} lies a triangular depressed surface, separated posteriorly
from the mesencephalon by a transverse groove and passing mesially into the stalk
of the pineal body. This triangular surface is termed the trigonum habenulm. It is
bounded laterally by the sukus habenulce. The mesial surface of the thalamus lies
in the third ventricle. It is covered with epithelium and is joined with that of
the opposite side by the middle commissure. The posterior rounded surface is
occupied almost entirely by the pulvinar. Below and external to this is the outer
geniculate body, which is placed just above the inner geniculate body before mentioned
(p. 105), the two being separated from one another by one of the roots of the optic

Fig. 82. — VIEW FROM ABOVE OF THE

THIRD VENTRICLE AND A VART OP
THE LATERAL VENTRICLES (Henle).

The brain has been sliced horizontally
immediately below the corpus callosum,
and the fornix and velum interpositum
have been removed.

Tho, thalamus options ; Ts, its ante-
rior tubercle ; Pv, pulvinar ; Com, middle
commissure stretching between the two
optic thalami across the middle of the
third ventricle ; Cf, columns of the for-
nix ; Cn, pineal gland projecting down-
wards and backwards between the superior
corpora quadrigemina ; &t, stria termi-
nalis ; Cs, nucleus caudatus of the corpus
striatum ; Vsl, ventricle of the septum
lucidum ; Ccl2, section of the genu of the
corpus callosum ; Pen, pineal peduncle ;
Tfo, pineal stria ; Cop, posterior com-
missure.

tract (upper brachium) (fig. 86).
From this brachium and from
the two geniculate bodies the
optic tract curves downwards
and forwards around the crus
cerebri.

The lateral and ventral sur-
faces of the thalamus are not
free, but are united with other
parts of the brain. The ventral
surface is united with a prolonga-
tion of the tegmental part of the
crus cerebri, and more anteriorly
the corpus albicans and the side
of the tuber cinereum lie below

it. The lateral surface is covered by white substance which is formed of the fibres
of the crusta, which here diverge into the substance of the hemisphere, and pass
between the thalamus and the lenticular nucleus as the internal capsule.

The thalami optici are covered on their free surfaces (mesial and dorsal)
(fig. 83), by a layer of white fibres, most marked upon the dorsal surface (stratum
zonale), and mainly running antero-posteriorly. On their outer surface, as just
mentioned, is the white matter of the inner capsule (i. c.} formed by fibres diverging
from the crusta into the hemispheres. Next to the thalamus on this side is a denser
layer of white fibres, termed the outer medullary lamina. All along this surface
radiating fibres pass out of the thalamus to mingle with the fibres of the inner
capsule and to pass with these to the surface of the cerebral hemispheres. Those in

\

Pv

1 1 •£ THALAM ENCEPHALON.

front pass to the frontal lobe of the hemisphere ; those in the middle region
to the posterior part of the frontal and to the parietal lobe, besides some to the
temporal lobe; those behind partly to the temporal lobe, but chiefly to the
occipital lobe. The fibres to the occipital lobe pass out from the lateral margin of
the pulvinar, and have at first a curved course round the posterior horn of the
lateral ventricle, afterwards radiating, with a generally sagittal direction, towards
the cortex of the occipital lobe. They are often spoken of as the optic radiations.
These radiating fibres are continuous with others passing from the optic tract to
the pulvinar. The lower surface of the thalamus is continuous posteriorly with the
prolongation of the tegmentum (subthalamic tegmental region), but in front this

Fig. 83. — SECTION ACROSS THE OPTIC

THALAMUS AND CORPUS STRIATUM
IN THE REGION OF THE MIDDLE COM-
MISSURE (E. A. S., after a prepara-
tion by Mr. S. G. Shattock). Natu-
ral size.

tli, thalamus ; a^e,i, its anterior, ex-
ternal and internal nuclei respectively ;
iv, its latticed layer ; m.c. , middle com-
missure ; above and below it is the cavity
of the third ventricle ; c.c. , corpus callo-
suiu ; /, fornix, separated from the third
ventricle and thalamus by the velum
interpositum. In the middle of this are
seen the two veins of Galen and the
choroid plexuses of the third ventricle ;
and at its edges the choroid plexuses of
the lateral ventricles ; t. s., taenia semi-

circularis : cr, forward prolongation of the crusta passing laterally into the internal capsule, i. c. ;
s. t. r., subthalamic prolongation of the tegmentum, consisting of (1) the dorsal layer, (2) the zona
inccrta, and (3) the nucleus of Luys ; s. n., substantia nigra ; n. c., nucleus caudatus of the corpus
htriatum ; n. I., nucleus lenticularis ; e. c., external capsule ; cl, claustrum ; /, island of Reil.

prolongation inclines to the outer side and becomes lost in a layer of grey matter
which is continuous internally with the grey matter of the floor of the ventricle,
and is seen at the base of the brain as the anterior perforated lamina. At its anterior
end the thalamus merges into a tract of fibres which stream from it through the
internal capsule into the frontal lobe of the hemisphere (anterior stalk of thalamus').
Other fibres curve downwards and outwards towards the white substance of the
hemisphere forming the so-called lower stalk of the thalamus (ansa peduncular is}.
Above this is another tract (ansa lenticularis), sweeping from under the thalamus
round the mesial part of the crusta to the lenticular nucleus of the corpus striatum.
The layer of grey substance which is interpolated between the two tracts may be
termed substantia interansalis ; including the two ansse it has been designated svb-
stantia innominata.1

The body of the thalamus is chiefly formed of grey matter with large and small
nerve-cells scattered in it, but their arrangement and connections with nerve-tracts
have not been satisfactorily ascertained. Its grey matter is partially subdivided into
two parts, the so-called inner and outer (mesial and lateral) nuclei of the thalamus
(Burdach), by a vertical white lamina, S-shaped in section (internal medullary
lamina). The lateral nucleus (e), is the larger and extends into the pulvinar ; it is
marked externally by the radiating white lines before mentioned as passing from
the thalamus into the inner capsule, and these confer upon its external layer some-
what of a reticulated aspect (latticed layer, w*). The mesial nucleus (i) does not
extend into the anterior tubercle, but this part of the grey substance of the

1 The term "anse pedonculaire " was originally used (by Qratiolet) to include the whole substantia
innominata.

SUBTHALAMIC TEGMENTAL REGION.

113

thalamus is cut off from it by another septum of white matter. The anterior
separated part is the anterior nucleus of the thalamus or nucleus of the anterior
tubercle (a). It contains comparatively large nerve-cells and from its depth a
number of fibres pass downwards and converge to form a well-marked bundle
(bundle of Vicq-d1 Azyr\ which, entering the corpus albicans, forms within that
tubercle a sharp bend, and appears to pass upwards again in the wall of the
ventricle as the anterior pillar of the fornix. There would seem, however, to be no
actual continuity between the two (see pp. 129, 130). The middle commissure
unites the mesial nuclei across the third ventricle, and is also continuous below
on each side with the grey matter of the cavity. It contains nerve-cells and
transversely coursing fibres, but many of the fibres are said to loop backwards
near the median plane in place of passing across to the opposite side.

In the trigonum habenulse is a collection of nerve-cells termed by Meynert
the ganglion of the habenula. To it, fibres pass from the peduncle of the pineal
body, and from it a bundle of fibres (fasciculus retroflexus, Meynerfs bundle (fig.

Fig. 84. — SECTION OF THE INTER-BRAIN NEAR THE JUNCTION WITH THE MID-BRAIN, SHOWING THE
SUBTHALAMIC TEGMENTAL REGION. Magnified about 2£ diameters. From a photograph (E. A. S. ).

The section passes nearly horizontally, so as to cut the fibres of the internal capsule across transversely.
It is just above and in front of the corpora mamillaria.

(., tasnia (attachment of epithelial roof of ventricle) ; r. ///. , ventriculus tertius ; sir., stria pinealis ;
Th., thalamus; n.t., mesial nucleus of thalamus; opt., optic fibres passing to pulvinar ; z.i., zona
incerta ; c.s., corpus subthalamicum ; c.i., capsula interna ; a. I., ansa lenticularis ; /., anterior pillar
of fornix passing backwards towards corpus albicans; V.A., bundle of Vicq d'Azyr, passing upwards
and forwards from corpus albicans into thalamus ; x. , white bundle containing a central nucleus of
grey matter ( ? the fasciculus retroflexus of Meynert) ; g, g', special groups of nerve-cells, of which ij
is the hinder end of the ganglion habenulse.

84, x) ) passes with a curved course through the tegmentum on the mesial side of
the red nucleus towards the place where the cerebral peduncles diverge ; where,

114 MESENOEPHALON.

according to Forel, it passes to another collection of nerve-cells, better marked in
most animals than in man, termed the interpeduncular ganglion (see p. 103).

Snbthalamic tegmental region ; transitional region. — The prolongation
of the tegmentum under the posterior part of the thalamus is divided by Forel into
three layers, which are named respectively from above down, the stratum dorsak,
the zona incerta, and the corpus subthalamicum or nucleus of Luys (fig. 83, 1, 2, 3).
The latter has here taken the place of the substantia nigra, lying next to the
prolongation of the crusta, the fibres of which are seen at the side of the subtha-
lamic tegmental region forming the internal capsule. The stratum dorsale consist
chiefly of fine longitudinal fibres — prolonged from the posterior longitudinal bundle
according to Meynert, or from the fibres enclosing the tegmental nucleus according
to Forel, possibly from both sources. The red nucleus of the tegmentum is pro-
longed into its posterior part, and from this a considerable number of fibres stream
into the internal medullary lamina of the thalamus, and a well-marked bundle
passes across the internal capsule to the lenticular nucleus. Some fibres of this
layer, which are traceable downwards into the upper fillet (Wernicke), turn into the
external medullary lamina of the thalamus, which lies along the mesial side of the
internal capsule, and from here they probably diverge into the white matter of the
hemisphere ; whilst others, coursing through the zona incerta, and crossing the
inner capsule, join a tract (ansa lenticularis, fig. 84, a.L and p. 112) which leads to
the lenticular nucleus of the corpus stratum. Finally another bundle of fibres is
said to be traceable from the mesial nucleus of the thalamus backwards through the
subthalamic region into the dorsal part of the posterior commissure, and thus over
the Sylvian aqueduct into the tegmentum of the opposite side.

The zona incerta is a reticular formation prolonged from that of the tegmentum ;
it passes anteriorly into the substantia interansalis.

The corpus subthalamicum, or nucleus of Luys (figs. 83, 84, e.s.), is a well-marked
brown stratum of grey matter containing numerous nerve-cells, and a close plexus
of very fine medullated fibres. It is lens-shaped in section, and has an enclosing
envelope of white substance, through which strands of fine fibres pass from the
interior of the body mesially towards the zona incerta, and outwards and downwards
through the internal capsule. This stratum is distinct only in the Primates.

The pineal body or gland (conarium, epiphysis cerebri) (fig. 82, Cn, fig. 91),
is a reddish body about the size of a small cherry-stone, and is named from its
supposed resemblance in shape to a fir-cone. It is connected with the posterior
part of the third ventricle, projecting backwards and downwards between the
superior pair of corpora quadrigemina. It is attached on each side by a broad
but flattened stalk of white fibres (pedunculus conarii) which is separated by the
pineal recess of the ventricle (p. 97) into a dorsal and ventral portion. The ventral
portion curves downwards ; it belongs to the ventral portion of the posterior
commissure. These fibres are said to - be derived from the optic tract near the
lateral geniculate body, and to go to the oculomotor nucleus of the opposite
side (compare p. 109). The upper portion extends on either side along the ridge-
like junction of the upper and mesial surfaces of the thalamus as the pineal
stria or tsenia fornicis (fig. 82, Tfo.}. At the sides the stalk merges into the
trigonum habenulse. The pia mater which invests the mesencephulon, covers the
pineal gland with a special investment before being prolonged as the velum inter-
positiim over the third ventricle and thalamus ; and the gland is liable to be torn
away in removing the pia mater.

The pineal gland is composed of a number of hollow follicles generally spherical,
but in some cases tubular, separated from one another by ingrowths of connective
tissue. The follicles are almost filled with epithelial cells and often contain much
gritty calcareous matter (acervulus cerebri, brain-sand), composed of microscopic

OPTIC THALAMI. 115

particles, aggregated into masses and formed of earthy salts (phosphate and
carbonate of lime, with a little phosphate of magnesia and ammonia) combined
with animal matter.

The same sandy matter is frequently found on the outside of the pineal body, or
deposited upon its peduncles. It is found also in the choroid plexuses ; and in a
scattered form occurs in other parts of the membranes of the brain. It occurs at
all ages, frequently in young children, and sometimes even in the foetus. It cannot,
therefore be regarded as the product of disease. The pineal body is larger in the
child and the female than in the adult male (Huschke). In the brains of other
mammals it is proportionally larger than in the human subject, and less loaded with
brain-sand.

The pineal body is developed originally as a hollow outgrowth from that part of
the embryonic brain which afterwards forms the third ventricle ; the diverticulum
becomes subsequently cut off from the ventricle, and undergoes ramification to form
tubes which are afterwards separated for the most part into isolated vesicles.

The pineal body is present in all vertebrates, Amphioxus only excepted. In
elasraobranch fishes and in most reptiles, as the researches of de Graaf, Baldwin
Spencer, and others, have shown, it is continued into a long tubular prolongation
from the third ventricle, which passes through an aperture in the skull (parietal
foramen) and ends under the skin in a small vesicle lined with ciliated epithelium.
But in some reptiles (e.g., Hatteria, blind-worm, lizard) this vesicle becomes
developed into a structure which bears a close resemblance to an invertebrate eye
(pineal eye), the part nearest the surface becoming thickened to form a kind of lens,
and the part connected with the stalk becoming pigmented and stratified like a
retina, whilst the stalk itself becomes solid and has nerve-fibres developed in it. It
is doubtful how far this structure serves as an eye in any living reptile, but in
certain extinct forms it was probably more completely developed. In birds and
mammals the pineal eye is not developed, but the organ is similar in structure to
that of man.

The posterior perforated space (locus perforatus posticus) (fig. 82, x ).
lies in a deep fossa (fossa Tarini, His) at the base of the brain, at the bottom of
which is greyish matter, connecting the diverging crura. It is perforated by
numerous small openings for the passage of blood-vessels ; and some horizontal
white striae usually pass out of the grey matter and turn round the peduncles close
to the upper border of the pons, entering which they reach eventually the medullary
centre of the cerebellum (tcenia pontis). It corresponds posteriorly, as far as a line
joining the anterior borders of the third nerves, to the floor of the aqueduct of
Sylvius, but in front of those nerves to the posterior part of the floor of the third
ventricle. In the grey matter over the space are a few scattered nerve-cells.

The corpora albicantia or mamillaria (fig. 32, a ; fig. 86) are two round
white eminences in front of this space, each about the size of a small pea, connected
together across the middle line. Each corpus albicans contains grey matter
concealed within its superficial white fibres, the nerve-cells being arranged in two
groups, the lateral and mesial (nuclei of the corpus albicans) ; of these the lateral
contains larger nerve-cells than the mesial.

The white matter of the corpora albicantia is formed by the anterior pillars of
the fornix : hence they have also been named bulbs ofthefornix; and by the bundle
of Vicq d'Azyr, which enters the anterior part of each tubercle at the dorso-mesial
aspect. Posteriorly each corpus albicans receives a bundle of nerve-fibres, which
is termed its peduncle. This, which in man is concealed within the grey matter of
the floor of the third ventricle, but which is seen at the base of the brain in many
animals, and is connected with the lateral nucleus of the body, is traceable to the
tegmentum and ultimately to the mesial part of the crusta (v. Gudden). In most
vertebrates there is but one (median) corpus albicans in place of two.

I 2

116 MESENCEPHALON.

An isolated bundle of one of the anterior pillars of the fornix is sometimes visible at the
base of the brain passing to the corpus albicans (stria alba tubcris. Lenhossek).

The tuber cinereum (fig. 86 ; fig. 82, i.e.} is a lamina of grey matter extending
forwards from the corpora albicantia to the optic commissure, to which it is attached.
It forms part of the floor of the third ventricle. In the middle it is prolonged
forwards and downwards into a hollow conical process, the infundibulum
(fig. 85, *'), to the extremity of which is fixed the pituitary body. On its outer
side close to the optic tract is a tract of grey matter with nerve-cells, termed by
Meynert the basal optic ganglion (see p. 119). According to Lenhossek this is
distinctly subdivided into three successive groups of nerve-cells, the most anterior
being just above the chiasma, the most posterior near the corpus albicans.

The pituitary body or hypophysis cerebri (figs. 32, 39, h, and fig. 85), formerly
called pituitary gland, from its being erroneously supposed to discharge pituita into
the nostrils, is a small reddish grey mass, of a somewhat flattened oval shape, widest
in the transverse direction, and occupying the sella turcica of the sphenoid bone.
The pituitary body has a special prolongation of the dura mater completely
enclosing it, except above where there is a small aperture for the passage of the
infundibulum (see p. 182). The body consists of two lobes, of which the anterior
is the larger, and is concave behind, where it embraces the smaller posterior lobe.
The two lobes are entirely different, both in their structure and development ; and
it is only in mammals that they come into close connexion with one another.

The posterior lobe is developed as a hollow downgrowth of the part of that cavity
of the embryonic brain, which afterwards becomes the third ventricle. In the
lower vertebrates, and especially in fishes, the cells which compose its walls become
converted into nerve-cells and -fibres, and as the lobus infundibuli it becomes an
integral part of the brain. But in the higher vertebrates it remains small and
almost undeveloped ; its cavity is obliterated, and all nervous structure becomes
obscured by the ingrowth of vessels and of connective tissue into the now solid
organ. The connective tissue forms reticulating bundles, between which occur

Fig. 85. — SAGITTAL SECTION OF THE PITUITARY BODY AND INFUNDI-
BULUM WITH THE ADJOINING PART OF THE THIRD VENTRICLE

(Schwalbe).

a, anterior lobe ; «', a projection from it towards the front of the
infundibulum, i ; It, posterior lobe connected by a solid stalk with the
infundibulum ; I.e. , lamina cinerea ; o, right optic nerve ; ch, section
of chiasma; r.o., recess of the ventricle above the chiasma; c.rn.,
corpus mamillare.

numerous spindle-shaped and branched cells, as well as a few larger corpuscles
containing pigment-granules in their protoplasm. Sometimes remains of the
original hollow are seen in the form of a cavity lined by columnar ciliated
cells.

The anterior lobe, darker in colour than the posterior, is developed as a tubular
prolongation from the epiblast of the buccal cavity, with which it is therefore
originally in connection, although it soon becomes separated by the growth of
intervening tissue. In the adult it is constituted by a large number of slightly
convoluted tubules or alveoli, similar to those of a secreting gland, and in like
manner lined by epithelium, which in some cases fills up the tubule. The tubules
are united by connective tissue, which is especially abundant in the neighbourhood
of the larger blood-vessels, and also forms a sort of capsule to the organ. Moreover,
portions of the tubules are frequently cut off by the connective tissue so as to form
isolated vesicles. The outer layer of epithelium is columnar ; and in some of the
larger tubes, especially those next to the posterior lobe, cilia may be detected on the
cells. The blood-vessels are numerous, and the capillaries form a close network

OPTIC TRACTS.

117

around the walls of the tubules. The lymphatics of the organ originate in cleft-
like spaces between the tubules and pass to a network in the capsule. In its
microscopic structure the anterior lobe of the pituitary body bears a resemblance
to the thyroid body, the vesicles of which are also originally a network of anasto-
mosing tubules, and in some animals remain throughout life in this condition.
Moreover, a colloid substance like that in the thyroid vesicles, is found sometimes
in the alveoli of the anterior lobe of the hypophysis.

In the middle line of the base of the brain, in front of the optic commissure, is
the anterior portion of the great longitudinal fissure, which separates the two
hemispheres. At .a short distance in front of the chiasma, this fissure is crossed
transversely by the anterior recurved extremity of the corpus callosum. On gently

int.qen-. b. sup. fcrach/.

oulvinar

\.rtf. larach.

rfc.gen-.b.

opt,, traiet »4-

anb.perf so

opt. nerve

Fig. 86. — ORIGIN AND RELATIONS OF
THE OPTIC TKACT (G. D. Thane).

The parts are viewed from below,
the mid-brain having been divided
transversely immediately above the
pons, and the pons, cerebellum and
medulla oblongata removed. The
lower part of the figure is the more
anterior.

turning back the optic com-
missure, a thin connecting
layer of grey substance, the
lamina cinerea. is seen oc-
cupying the space between
the corpus callosum and the
chiasma, and continuous above
the chiasma with the tuber

cinereum. It is connected at the sides with the grey substance of the anterior
perforated space, and forms part of the anterior boundary of the third ventricle
(fig. 57, p. 70) : it is somewhat liable to be torn in removing the brain from the
skull ; and, in that case, an aperture is made into the fore part of the third ventricle.

The optic tracts and optic commissure or chiasma. The optic tracts curve
round the crusta on each side to unite with one another immediately in front of the
tuber cinereum, where they form the X-shaped commissure which is known as the
chiasma. The optic tracts form the posterior limbs of the X ; the optic nerves,
passing into the optic foramina, the anterior limbs (fig. 86).

Each tract arises posteriorly by a broad root, which is divided by a longitudinal
groove into two distinct parts, a lateral and a mesial. The lateral root is the larger.
It is connected with and emerges from the posterior and ventral part of the thalamus
(lateral geniculate body and pulvinar), and is partly continuous with the brachium
of the superior quadrigeminal body. The mesial root, when traced backwards, is
seen to curve round the crusta and then to lose itself beneath the mesial geniculate
body, in which it appears to end, although it may perhaps ultimately pass into the
inferior quadrigeminal body as its brachium. Although this root appears connected
with the internal geniculate body, it is doubtful if there is any functional connexion
between this body and the optic nerve, the part of the tract which enters the mesial
geniculate body being Gudden's commissure, which joins the mesial geniculate bodies
of the two sides (see below). Before reaching the chiasma the optic tract lies
postero-mesially to the anterior perforated space.

Darkschewitsch describes the passage of some of the fibres of the optic tracb to the
ganglion habenulae and pineal peduncle, and ultimately by the posterior commissure to the
oculomotor nucleus (compare pp. 109 and 114). He regards these as fibres subserving the reflex
changes of the pupil.

As for the course of the optic fibres in the tract and chiasma it may be stated

118 MESENCEPHALON.

that although in many mammals (mouse, guinea-pig), and in all vertebrates below
mammals, the decussation is complete, so that all the fibres pass from one tract
into the opposite optic nerve, in other mammals (rabbit, dog, cat, monkey) and
in man, it is incomplete, so that some of the fibres from the left optic nerve pass
into the left tract and others into the right tract, and the same mutatis mutandis
for those of the right nerve. This fact has been conclusively proved both by
experiment and clinical observation. At the same time it must be stated that cases
have occasionally been recorded which, if correct, are only to be explained on the
supposition that the crossing is complete : in these we must suppose that there has
been a reversion to the lower and more primitive type of chiasma..

The two sets of nerve-fibres are usually spoken of as the crossed and uncrossed
bundles, although they are not to be regarded as formed into entirely separate
funiculi, nor are their limits sharply defined either in the nerve, chiasma, or tract.
The uncrossed bundle is distributed exactly to the lateral half of the retina, the
crossed bundle to the mesial half ; and on the whole the fibres of the uncrossed
bundle keep to the lateral side of the optic nerve, whilst the crossed bundle is on
the mesial side of the nerve. In the chiasma and tract they are usually more
commingled, and their relative position is very variously described. In a case of
atrophy of one nerve which has been clearly described by Williamson, the uncrossed
fibres chiefly occupied the middle of the tract, the crossed being chiefly at the
periphery and lower part. Similar results were obtained by Henschen.

According to Salzer's enumeration, there are nearly half a million fibres in each optic nerve.
The fibres vary in size. According to v. Gudden they are divisible, according to their calibre,
into two classes, finer and coarser. The former of these he regarded as being concerned in
the production, as afferent fibres, of the pupil-reflexes, the latter as conveying visual impressions.
The finer fibres degenerate after destruction of the anterior corpora quadrigemina (in the cat
and rabbit). It must be remembered that not only afferent, but also efferent impressions are
carried by the optic tracts ; governing the chemical changes which occur in the retina, and
also the movements of some of its elements (pigment-cells, cones).

Besides the optic nerve-fibres, there is a bundle at the posterior part of the
chiasma, and running along the mesial side of the optic tracts to join the internal
geniculate bodies of the two sides.1 This is known as the inferior commissure or
commissure of Gudden. It appears to have no relation to the visual function, for it
undergoes no change when the rest of the optic tracts become atrophied after extir-
pation of both eyes in young animals. Its fibres are of extremely small diameter.

In structure the optic tract resembles an extension of the white matter of the
brain, being very soft and not divided up into bundles by connective tissue, nor are
its fibres provided with membranous sheaths. These structures are found, however,
in the chiasma, and in the optic nerve, which are strong and tough and invested
with sheaths continuous with the pia mater and arachnoid. At its entrance into
the orbit the optic nerve receives a strong investment from the dura mater, which
is continued around it into the sclerotic coat of the eye. The nerve is subdivided
by intercommunicating connective-tissue septa into a large number of compartments,
which contain the nerve-fibres, but the latter are not gathered up into round funiculi
invested by perineurium, as in .the case of the ordinary peripheral nerves.

Stilling has described the optic tract as sending a prolongation directly into the outer part
of the crus cerebri. This prolongation is said to contain fibres which pass (1) to the oculo-
motor nuclei ; (2) to the cerebellum by the inferior peduncle : (3) to the pons Varolii, even
extending to the inferior olive.

The name traetus transrersus pcdvnculi was given by Gudden to a band of fibres, first
noticed by Inzani and Lemoigne, which is sometimes seen emerging from the base of the
anterior quadrigeminal body, and coursing obliquely over the brachia of the quadrigeminal
bodies to enter the crus cerebri. It is much better marked in some animals than in man.
It becomes atrophied after extirpation of the eye, and may be a part of the prolongation
of the optic tract described by Stilling.

1 It is stated by Darkschewitsch, that this commissure unites each mesial geniculate body with
the lenticular nucleus of the opposite side.

OPTIC TRACTS.

119

.tc.. lol.

As regards the course of the optic fibres, the results of experiment show that
whilst some have their cell-origin in the periphery — presumably in the nerve-cells
of the retina — others take origin in nerve-cells of parts of the brain (superior
corpora quadrigemina, external geniculate body, and pulvinar). Of those nerve-
fibres which have their cell-origin in the retina, and which, therefore, undergo
degeneration backwards after section of the optic nerve or tract, some end by
arborisations between the nerve cells of the external geniculate body and pulvinar,
others by arborisations in the more superficial layers of the superior corpora quadri-
gemina (see figs. 79, 80, and
87). It has been found
that after enucleation of
the eye the grey matter
between the cells in these
several parts undergoes
atrophy. Those fibres which
have their cell-origin in the
nerve-centres end by ter-
minal arborisations within
the retina. Their course
will there be followed in
the part of this work which
deals with the structure of
the eye.

Finally, whilst dealing
with the course of the
optic nerve-fibres, it may
-be as well to mention the
probable intercentral con-
nections of the nervous
visual apparatus. (1.) There
is in all probability a double
connection between the cor-
tex of the occipital lobe
(which represents the higher
visual centre) and the lower
visual centres of the thala-
mencephalon and mesen-
cephalon by two sets of
fibres, one set arising from
the cortex and passing
through the corona radiata
and caudal end of the in-
ternal capsule, finding their

terminal arborisation in the grey matter of the lower optic centres, and another set
arising in cells of those centres and finding their terminal arborisation in the
occipital cortex. These connections are confined to the parts of the same side of the
brain ; there is no evidence of any crossing of the fibres. (2.) There appears to
be an intimate connection between the lower optic centres and the grey matter of
the bulb and cord. This connection is probably mainly effected through the upper
fillet. (3.) The nuclei of the nerves to the muscles of the globe of the eye, both
external and internal, are certainly connected with the optic centres. It is possible
that this connection may be partly effected through the posterior commissure and
posterior longitudinal bundle ; it is probably both crossed and uncrossed : but the

otorias

cereliri

Fig. 87. — DIAGRAM OF THE PROBABLE COURSE AND RELATIONS

OF SOME OF THE OPTIC FIBRES.

120 RECENT LITERATURE OF THE MID-BRAIN AND INTER-BRAIN.

actual tracts of connection have not yet been elucidated. (4.) There appears to
be a direct connection between some of the fibres of the optic tract and the cere-
bellum, since after removal of one half of the latter organ, many of the fibres of
the corresponding optic tract undergo the Wallerian degeneration (Marchi). This
connection may also take place along the tract of the upper fillet.

In the grey matter which lies between the third ventricle and the optic chiasma,
a small collection of nerve cells (basal optic ganglion) is seen on each side, as already
noticed (p. 116). These ganglia do not appear to have any direct connection with
the optic nerve, as was supposed by Meynert to be the case, but from each a tract
issues, which, after decussating with that of the opposite side (Meymrfs commissure),
applies itself to the mesial side of the optic tract, close to Gudden's commissure, and
passes backwards to the subthalamic region to enter the nucleus of Luys, and
perhaps to be connected with the continuation of the upper fillet. Antero-laterally
this tract may be connected, beyond the basal optic ganglion, with the lenticular
nucleus.

RECENT LITERATURE.

Ahlborn, F., Ueber die Bedeutung der Zirbeldriise, Zeitschr. f. wiss. Zool., Bd. xl., 1884.
Amalcli, P., Contribute aWanatomia fina della-regione peduncolare, &c., Rivista sperimentale di
freniatria, Vol. xviii., 1892.

Bechterew, W., Experim. Untersuchungen u. d. Kreuzung d. Sehnervenfasern im Chiasma, Neurol.
Centralbl., 1883 ; Ueber den Verlauf der Sehnervcnfasern, <L-c., ibid. ; Ueber die nach Durchschneidung
der Sehnervenfas'ern im Innern der Grosshirnhemispharen (in der Nachbarschaft deshinterenAbschnittes
der inneren Kapsel) auftretenden Erscheinunyen, Neurol. Centralb]., .1884 ; Degeneratianen des
Hirnschenkcls, Arch. f. Psych., xix., and Neurol. Centralbl., 1885, 1886, and 1887.

Bellcmci. G. , La terminaison centrale du nerf optique chcz les mammiferes, Arch. ital. de biologie,
t. vi., 1885 ; also in Zeitschr. f. wissensch. Zoo!., Bd. xlvii., 1888.

Beraneck, E., Ueber das Parietalauae der Reptttien, Jenaische Zeitschr. f. Naturw., Bd. xxi.,
1887.

Bernheimer, S., Ueber die Entwickelung u. d. Verlauf der Markfasern im Chiasma, &c.,
Wiesbaden, 1889 ; Ue. d. Sehnervenwurzeln des Menschen, 'Wiesbaden, 1891 ; and Verhandl. d.
lOten internat. Congress, Berlin, 1890.

Burdach, F. , Zur Faserkreuzung im Chiasma und in den Tractus nervorum opticorum, Archiv
f. Ophthalmologie, Bd. xxix., 1883.

Cattle, J. Th., Recherches sur la glandc pineale des plagiostomes, <L-c., Arch, de biologie, t. iii.,
1882.

Cionini, A., Sulla struttura d. ghiandola pineali, Riv. sperim. di freniatri, 1885 and 1888.
Darkschewitsch, L., Zur Anatomic d. Corpus quadrigeminum, Neurol. Centralbl,, 1885 :
Ueber die hintere Commissur des Gehirns, ibid., 1885 ; Einige Bemerkungen u. d. Faserverlauf in d.
hinteren Commissur, ibid., 1886; Zur Anatomic der Glandula pinealis, Neurol. Centralbl., 1886;
Ueber die PupiUar-fasern d. Tractus options, Abstract from the Russian in Neurol. Centralbl., 1887 ;
Ueber die sogennanten primaren Opticus-ce-ntren u. Hire Beziehung zur Grosshirnrinde, Arch. f. Anat.
u. Physiol., Anat. Abth., 1886 ; Ueber d. Kreuzung der Sehnervenfasern, Arch. f. Ophth., Bd. xxxvii. ;
Ueber den oberen Kern des N. oculomotorius, Archiv f. Anat. u. Physiol., Anat. Abth., 1889.

Darkschewitsch, L., und Pribytkow, G., Ueber die Fasersysteme am JBoden des dritten
Hirnventrikels, Neurol. Centralbl., 1891.

Dostoiewsky, A., Ueber den Bau der Vorderlappen des Hirnanhanges, Archiv f. mikr. Anatomic,
Bd. xxvi., 1886.

Duval, M., Le troisieme ceil des vertebre's, Journal de Micrographie, 1888.
Edinger, Ueber einige Fasersysteme des Mittelhirns, Neurol. Centralbl., 1890.
Flechsig-, P., Weitere Mittheilungen il. d. Beziehungen d. unt. Vierhugels z/um HiJrnerven,
Neurol. Centralbl., 1890.

Flesch, Ueber den Bau der Hypophyse, Tageblatt der 57 Versamml. deutsch. Naturf. u. Aerzte in
Magdeburg, No. 4, 1884 ; Ueber die Hypophyae einiger Saugethicre, Tagebl. d. Naturforscherver-
sammlung in Strassburg, 1885.

Forel, A., Einige hirnanatomische Betrachtungen u. Ergebnisse, Arch. f. Psych., Bd. xviii., 1887.
Furstner, Weitere Mittheilung iiler den Einfluss einseitiger Bulbuszerstorung auf die Entwick-
lung der Hirnhernispharen, Archiv f. Psychiatrie, Bd. xii. , 1882.

G-anser, Ue. d. periphere u. centrale Anordnung d. Sehnervenfasern u. ueber d. Corpus bigem.
anterius, Archiv f. Psychiatrie, xvi., 1882 ; Vergleichend-anatom.Studien ii. d. Gehirn des Maulwurfs,
Morph. Jahrb., Bd. vii., 1882.

de Graaf, H. "W. , Zur Anatomic und Entwicklung der Epiphyse bei Amphibien und Reptilien,
Zoolog. Anzeiger, 1886 ; Bijdrage tot de kennir van den bouw en de ontwikkeling der epiphysc bij
Amphibien en Reptilien, Leiden, 1886.

von Gudden, Ueber die Kerne der Augenbewegungsnerven ; Ueber den Nervenfasereerlauf im
Opticus und in der Retina, Deutsche Naturforscherversammlung zu Salzburg, 1882 ; Ueber das Corpus
mamillare und den soy. Schenkel der Fornix, Allg. Zeitschr. f. Psychiatrie, Bd. xli., 1885 ; Ueber

RECENT LITERATURE OF THE MID-BRAIN AND INTER-BRAIN. 121 •

die Sehnerven, die Sehtractus, <L-c., Tagebl. d. deutsch. Naturforscherversamralung, 1885 (Neurol.
Centralbl. ) ; also in Gesammelte A bhandlungen.

Hamilton, D. J., On the cortical connexions of the optic nerves, Proceedings of the Royal Soc. of
London, Vol. xxxvii., 1884.

Hebold, O. , Der Fascrverlauf im Sehnerven, Neurol. Centralbl., 1891.

Held, H., J)er Ursprung destiefen Markes der Vierhiigelregion, Neurol. Centralbl., 1S90.

Henschen, Experimentelle u. patholog. Untersuchungen u. d. Gehirn, 2 vols., Upsala, 1890 and
1892.

Hensen und Voelckers, Ueber den Ursprung der Accommodationsnerven, n. Bemerkungen
iiber d. Function d. Wurzelnd. Nermis oculomotor ius, Arch. f. Ophthaltu., Bel. xxiv., 1878.

Honeg-ger, J., Vergleich.-anatom. Untersuchungen iiber den Fcrnix, iL-c., Recueil zool. suisse,
t. v., 1890.

Jatzow, R. , Beitrag zur Kenntniss der retrobulbdren Propagation des Chorioidealsarkoms und
zur Fnif/e des Faserverlaufs im Sehnervengebiete, Archiv f. Ophthalmologie, Bd. xxxi., 1885.

Julin. Ch., De la signification morphologique de I'epiphyse (glande pineale) des vertebres, Bullet,
scientifique du Nord de la France et de la Belgique, 1887.

Koppen, Ue. d. hintere Ldngsbiindel, Tagebl. d. deutsch. Naturforscherversamml. in Heidelberg,
1890.

Leydig, F., Das Parietalorgan der Wirbelthiere, Zoolog. Anzeiger. , 1887.

Lothring-er, S. , Unterschungen an der Hypophyse einiger Sdugethiere und des Menschen,
Archiv f. mikr. Anat. , Bd. xxviii. , 1886.

Marchand, Beitrag z. Kenntniss der homonymen bilateralen Hemianopsie u. d. Faserki'euzung
imChiasma, Archiv f. Ophthalnu., Bd. xxviii., 1882.

Marchi, V., Sulla struttura del talami ottici, Rivista sperim. di freniatria, 1884 and 1887.

Minguzzini, Q. , Sur la fine structure de la substantia nigra Soemmeringii, Archives ital. de
biologic, xii., 1889.

v. Monakow, Experimentelle und patholoyisch-anatomische Untersuchungen iiber die Beziehunqen
der sogenannten Sehsphdre zu, den infra-corticalen Opticuscentren und zum N. opticus, Archiv f.
Psychiatric, Bde. xiv., xvi., xx., xxii., xxiii., xxiv. ; and Arch. f. Anat. u. Physiol.. Physiol. Abth.,
1885.

Nussbaum, J. , Ueber die wechselseitigen Beziehungen zwischen den centralen Ursprungsgebieten
der Augenmuskelnerven, Wiener med. Jahrb., 1887.

Onodi, A. D., Ueber die Verbinduny des Nervus opticus mit dem Tuber cinereum, Internal.
Monatsschr. f. Anat. u. Histol., iii., 1886.

Parinaud, H., Des rapports croises et directs des nerfs optiques avec les hemispheres ctrebraux,
Comptes rendus de la Soc. de la biol., 1882.

Pemberton, H. R., Recent investigations on the structure and relations of the optic thalami,
Journal of Comp. Neurology, i., 1891.

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1889.

Richter, Zur Frage der optischen Leitungsbahnen des inenschlichen Gehirns, Arch. f. Psychiatric,
Bd. xvi., 1885.

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Harvard College, xx., 1891.

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Abth. Hi., Bd. lv., 1888.

Spencer, W. Baldwin, Preliminary Communication on the Structure and Presence in Sphenodon
and other Lizards of the Median Eye described by von Graafin Anguis fragUis, Proceedings of the Roy.
Soc., vol. xl., 1886 ; On the Presence and Structure of the Pineal Eye in Lacertilia, Quart. Journ. of
Micr. Science, Oct., 1886.

Spitzka, E. C., Contrib. to the Anatomy of the Lemniscus, The Medical Record, 1884 ; Vorldunc/e
Mittheiiung ii. einige Resultate, hauptschl. d. Cummissura posterior betreffend, Neurol. Centralbl.,
1885.

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di sci. e lettere, xvi., 1891.

Stilling1, J., Untersuchungen uber den Bau der optischen Centralorgane, I. Theil; Chiasma und
Tractus opticus, 1882.

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R. Institute Lombardo di Milano, 1885 ; Sail' anatomia minuta dette eminenze bigemine anteriori delV
uomo, Archivio italiano per le malattie nervose, 1885.

Tartuffi., Tratto ottico en corpi gcnicolati, Rivista sperimentali di freniatria, 1882.
Westphal, C., Ueber einen Fall von chronischer progressiver Ldhmung der Augenmurkeln nebst
Beschreibung von Ganglienzellenyruppen im Bereiche des Oculomotwius- Kernes, Archiv f. Psychiatric,
Bd. xviii.,1887 ; Ueber GangUenzellengruppen im Niveau des Oculomotorius-Kernes, Neurol. Centralbl.,
1887.

"Williamson, R. T. , The changes in the optic tracts and chiasma in a case of unilateral optic atrophy
Brain, 1892.

Zacher, Th., Beitr. zur Kenntniss d. Faserverlaufs im Pes Pedunculi, &c., Arch. f. Psych.,
Bd. xxii., 1891.

122 THE LATERAL VENTRICLES.

THE LATERAL VENTRICLES AND THE PARTS OP THE BRAIN

DEVELOPED IN CONNEXION WITH THEM: CORPORA STRIATA:

CEREBRAL HEMISPHERES (PROSENCEPHALON).

The lateral ventricles ; ventricles of the cerebral hemispheres. — An

aperture (foramen of Monro) which has been already mentioned as opening out of
the anterior part of the third ventricle (see p. 97) leads on each side into the
corresponding ventricle of the cerebral hemisphere or lateral ventricle (figs. 88, 89).
Each lateral ventricle is an irregularly curved cavity, extending in the substance of
the corresponding hemisphere for about two-thirds of its entire length, and lined
by a prolongation of the ciliated epithelium which characterises the inner surface
of the true brain-ventricles. It may be described as consisting of a body, an anterior
horn, a posterior horn, and a middle, lateral, or descending horn. The anterior horn
curves from the foramen of Monro somewhat outwards, with a slight inclination
downwards into the frontal lobe ; the body comprises that part of the cavity which
extends from the foramen of Monro to its bifurcation into posterior and descending
horns opposite the splenium of the corpus callosum, and is separated anteriorly from
its fellow of the opposite hemisphere by a thin septum, the septum lucidum ; the
posterior horn passes backwards, with a bold curve convex outwards, into the
occipital lobe ; and the descending horn passes forwards and slightly downwards also
in a bold curve with its convexity outwards, into the temporal lobe, and extends to
about an inch from the apex of that lobe. The anterior horn is directly continued
from the body of the ventricle, and may therefore be described along with it.

The body and anterior horn of the ventricle are roofed over by the corpus
callosum, with its lateral extension into the substance of the hemisphere. In
examining the ventricles from above it is usual to slice the brain horizontally down
to the level of the callosum, and then to cut through this commissure a short
distance on each side of the middle line, and remove it sufficiently to expose the interior
of the ventricle. The following parts are thereby brought to view, from within, out-
wards, or laterally : (a) Theedgeof the fornix (figs. 88, 89,/), a flattened tract of white
matter with longitudinal fibres, which lies immediately under the callosum, broaden-
ing behind as it passes under the splenium, and bifurcating in front into two
cylindrical bundles, each of which passes over the foramen of Monro, and in front
of that foramen into the mesial part of the subthalamic tegmentum. (£) If the
callosum and fornix are removed, a layer of pia mater is seen underneath. This is
the velum interposition (fig. 94), and its edge projects as the choroid plexus of
the lateral ventricle from beneath the margin of the fornix in the form of a
vascular fringe (figs. 88, 89, pi. ch.), which extends from the foramen of Monro (at the
back of which it is continuous with the corresponding plexus of the opposite side as
well as with those of the third ventricle) over the surface of the thalamus, as far as
the descending cornu, into which it projects along the whole length of the horn
(mesial border), (c) Lateral and anterior to the choroid plexus two masses of grey
matter, separated by an obliquely-placed white stria, form the floor of the ventricle.
The mesial and narrower of these is a part of the dorsal surface of the thalamus (fig. 88,
th. opt.) ; it extends from the foramen of Monro to the posterior limit of the body of the
ventricle and is covered with a thin layer of white matter. The white stria is the
twnia semicircularis or stria terminalis (fig. 8'2,St.). A vein (vein of the corpus striatum)
runs superficial to the tasnia, and passes in front, at the foramen of Monro, into the
vein of Galen of the velum interpositum. Close to the ependyma and lying over
this vein of the corpus striatum is a small greyish band, containing longitudinally
running nerve-fibres : this has been named the lamina cornea. The lateral mass of

THE LATERAL VENTRICLES.

5.0

Fig. 88. — VIEW OF THE LATERAL VENTRICLE FROM ABOVE. Natural size. (E. A. S. and Q-. D. T.)

The preparation was made with the brain in situ (hardened). The skull cap and membranes having
been removed, the brain was sliced down to the level of the corpus callosum. The left lateral ventricle
was then opened by cutting away its roof, and the island exposed by slicing away the opercula. The
drawing is made from a photograph.

I.R. , insula Reilii (the line points to the middle of the three gyri breves) ; s.c. , sulcus centralis
insulse ; g.L, gyrus longus insulse ; c.c., corpus callosum ; n.L., nerves of Lancisi ; str.t., stria tecta ;
/.mi., forceps minor; /.»;«., forceps major; c.a., cornu anterius of ventricle; c.p., cornu posterius ;
c.i., entrance to cornu inferius ; f.M., foramen Monroi ; s.M., sulcus leading backwards to the foramen
Monroi ; c.str., corpus striatum ; th.opt., thalamus opticus, anterior tubercle ; pl.ch., plexus choroides ;
/, fornix ; /', its anterior pillar; h, posterior end of hippocampus major; tri., trigonum ventriculi ;
calcar, calcar avis.

124 THE LATERAL VENTRICLES.

grey matter is the nucleus caudatus of the corpus striatum (c. sir.} It is pear-shaped, with
the larger end projecting into the floor of the anterior horn, and the smaller tapering
posterior end (tail) extending to the origin of the descending horn, and then curving
downwards and forwards along the dorsal part of this horn, in which it forms a
long, narrow, rounded eminence. The posterior horn (figs. 88, 89, c.p.), which
is curved around the parie to- occipital fissure, its concavity therefore being
directed inwards, passes, as before said, into the occipital lobe. It is roofed by the
fibres of the corpus callosum which are passing to the temporal and occipital lobes ;
part of these fibres also form its lateral wall. At the upper part of its mesial wall
there is a bundle of fibres (forceps major) sweeping round from the splenium of the
callosum to enter the occipital lobe. This produces a projection into the cavity of
the horn, which is known as the lulb of the posterior horn. Below it is another
curved eminence, which extends from the base of the horn backwards for a variable
distance, to end in a pointed extremity : this is termed, from its resemblance to a
cock's spur, the ergot (Morand), or calcar avis (also hippocampus minor). It
corresponds with the calcarine fissure on the mesial surface of the hemisphere.

The hippocampus minor is not peculiar to the human brain as was at one time thought, but
is found in the brains of quadrumana. In the human subject the posterior horn varies
greatly in size, and the hippocampus minor is still more variable in its development, being
sometimes scarcely to be recognised, and at others proportionally large. It is usually most
developed where the posterior horn is longest ; but the length of the posterior horn, and
prominence of the hippocampus minor, are by no means in proportion to the dimensions
of the hemisphere.

The middle, lateral, or descending horn (fig. 89) is directed at first back-
wards and outwards from the posterior end of the body of the ventricle ; it then
passes downwards and forwards with a bold sweep (at about the plane of the parallel
sulcus), being finally curved inwards, and ending about an inch from the apex of
the temporal lobe, where it abuts against the amygdala. The dorso-lateral boundary
(roof) is formed by the fibres of the callosum, which are arching over it into the
temporal lobe, forming the so-called tupetum. The tail of the nucleus caudatus
and the taenia semicircularis are prolonged into the roof. Extending along the floor
of the horn is an eminence known as the hippocampus major or cornu Ammonis (fig.
89, ti), which becomes enlarged as it descends, and being notched, its edge here
presents a certain resemblance to an animal's paw (pes hippocampi). This eminence
corresponds with the hippocampal fissure externally, which thus indents the floor
of the cornu, and the grey matter at the bottom of the fissure being separated from
the cavity of the ventricle by a thin layer of white substance (covered with ependyma"),
shews through and gives a bluish-white appearance to the hippocampus. Mesial to
the hippocampus is the white band known as the fimbria (fig. 89,./z), prolonged from
the posterior pillar of the fornix ; and over the fimbria, at the angle which the floor
of the horn here forms with its roof, the choroid plexus projects into the cavity from
the external pia mater ; the plexus is, however, covered by the epithelial lining
of the cavity which extends over it in passing from roof to floor. If the pia mater
is pulled away it drags along with it this covering layer of epithelium, and the cornu
is made to open on the mesial surface of the brain. A cleft-like opening is thus
produced, which has been called the inferior fissure of the c&rebrum, being the
lower part of the so-called transverse fissure, which follows the plane of the velum
interpositum (see p. 184) over the thalamus and third ventricle, and emerges over
the corpora quadrigemina. It is along this fissure that the choroid plexuses of the
pia mater are invaginated into the ventricles, covered by the ventricular epithelium,
which is pushed in before them. It is only when the choroid plexuses are dragged
away that an actual fissure is formed in the hemisphere-wall between the fornix
and fimbria on the one side and the optic thalamus on the other ; but with the

THE DESCENDING HORN.

125

Fig. 89. — VIEW FROM ABOVE AND THE SIDE OP THE WHOLE LEFT LATERAL VENTRICLE.
Natural size. (E. A. S. and Gr. D. T. )

This is a further dissection of the preparation .shown in fig. 88. The insula has been sliced away
and the middle or descending cornu, c.i., exposed. Within this are seen the following parts : fi, fimbria,
continued from the fornix ; k, the hippocampus major ; coll., the eminentia collateralis. The other
lettering as in fig. 88.

126

THE LATERAL VENTRICLES.

plexus in situ it is a deep sulcus, i.e., an invagination only, of the thin hemisphere-
wall (here formed of the ventricular epithelium alone). It is known as the choroidal
fissure, and appears at an early period of embryonic development.

Merkel and Mierzejewsky have described an actual cleft in the pia mater along the descend-
ing horn which effects a communication between the ventricle and the subarachnoid space,
analogous to the foramen of Majendie and the lateral apertures in the fourth ventricle. This
observation has not hitherto been confirmed.

Fig. 90. — Two VIEWS OF A PLASTER CAST OP THE CAVITIES OF THE CEREBRAL VENTRICLES.

(After Welcker.)

A, from above ; B, from the side. The projections into the cavities of the structures which
bound the ventricles are seen as impressions upon the cast.

At the junction of the descending with the posterior cornu, and occupying the
angle between the hippocampus major and the calcar, is a triangular space, the
floor of which is mainly occupied by a smooth, somewhat raised surface, which
extends backwards into the posterior cornu, and is often continued downwards into
a longitudinal eminence which passes for some distance in the inferior horn alongside

THE CORPUS CALLOSUM.

127

of and lateral to the hippocampus major. This eminence corresponds with the
collateral fissure externally, and is known as the eminentia collateralis or pes acces-
sorius (fig. 89, coll.} ; this term is also by some authors used to include the smooth
eminence at the junction of the cornua. The triangular space at this junction is
termed by Schwalbe trigonum ventriculi.

The shape of the ventricles is best shown in a cast of the cavities, which can be
made in plaster of Paris. The appearance of such a cast, viewed respectively from
above and from the side, is given in the accompanying figure (fig. 90, A, B).

The corpus callosum or great commissure (trabs cerebri) (figs. 91. 92, 102),
a white structure, about 10 centimeters long, which connects the two hemispheres
throughout nearly half their length, approaches closer to the front than the back of

for. Man,

cpfc. luc. \

r \ s

pineal stria,
post. comm.
pineal bodu

monticuius

in^aaaib
pit.

tub. valv.

Fig. 9J. — PORTION OF A MEDIAN SECTION OF THE BKAIN, SHOWING THE CORPUS CALLOSUM, THIRD

VENTRICLE, AQUEDUCT AND FOURTH VENTRICLE, PONS, CEREBELLUM, ETC. (G. D. T. ) f.

the hemispheres. It is about 20 mm. in width behind, and somewhat narrower in
front. Its thickness is greater at the ends than in the middle, and is greatest
behind (8 mm.). It is arched from before backwards, its lower surface being
concave and its upper surface convex. Its upper surface is distinctly marked by
transverse furrows, which indicate the direction of the greater number of its fibres.
It is also marked in the middle by a longitudinal furrow (raphe), which is bounded
by two white tracts, placed close to each other, named the mesial longitudinal stria
or nerves of Lancisi (fig. 88). On each side, near the margin, are seen other
longitudinal lines (grey or lateral longitudinal strife). The lateral striae lie within a
fissure (callosalfissure) which separates the upper surface of the commissure from
the gyrus fornicatus (by which convolution they are entirely covered in : hence the
name, ta-nm tectm, which is often applied to them). Both the mesial and lateral
longitudinal striae are traceable, when well developed, into the gyrus dentatus
posteriorly. The morphological value of these structures will be afterwards referred
to (p. 155).

In front, the corpus callosum is reflected downwards and backwards, forming a

]28

THE LATERAL VENTRICLES.

bend named the genu (fig. 91). The inferior or reflected portion, which is named
the rostrum, becomes gradually narrower as it descends, and is connected with the
lamina cinerea by a thin white layer, the commissura baseos alba of Henle. It gives
off also two bands of white substance, the peduncles of the corpus callosum, which,
diverging from one another, run backwards across the posterior margin of the
anterior perforated space on each side to the tip of the temporal lobe, where they
meet the inner olfactory roots. These peduncles traced upwards around the genu
are found to be continued into the mesial longitudinal striae.

Behind, the corpus callosum terminates in a free thickened border, named the
splenium, but this term is sometimes restricted to the under part of this thickened
border, which appears as if rolled round under the rest (splenium proper, Beevor).

Fig. 92. — VIEW OF THE CORPUS CALLOSUM FROM ABOVE (from Sappey after Foville). J

The upper surface of the corpus callosum has been fully exposed by separating the cerebral hemi-
spheres and throwing them to the side ; the gyrus fornicatus has been partly detached, and the trans-
verse fibres of the corpus callosum traced for some distance into the cerebral medullary substance.

1, the upper surface of the corpus callosum ; 2, median furrow or raphe ; 3, longitudinal strise
bounding the furrow ; 4, swelling formed by the transverse bands as they pass into the cerebrum,
arching over the side of the lateral ventricle ; 5, anterior extremity or knee of the corpus callosum ; 6,
posterior extremity ; 7, anterior, and 8, posterior fibres proceeding from the corpus callosum into the
frontal and occipital lobes respectively ; 9, margin of the swelling ; 10, anterior part of the gyrus
fornicatus ; 11, fissure between the corpus callosum and this convolution opened out ; outside 12, is the
termination of the calloso-marginal fissure, and before 13 is the parieto-occipital fissure ; 13, upper
surface of the cerebellum.

The mesial part of the under surface of the corpus callosum is connected behind
with the fornix, and in the rest of its length with the septum lucidum, a vertical
partition between the two lateral ventricles, which is included in the anterior bend
of the corpus callosum. On the sides the corpus callosum roofs in the body and
anterior horn of the lateral ventricles. The enlarged posterior part or splenium lies
over the mesencephalon, with pia mater between. The transverse fibres of the
corpus callosum pass in a radiating manner, interlacing with those of the internal
capsule, through the medullary centre to the cortex of each hemisphere. Those in
front which sweep round into the prefrontal region form the so-called forceps minor.

THE FORNIX. 129

Those from the body and the upper part of the splenium which curve over the
lateral ventricle form the tapetum, whilst a large mass of fibres from the
splenium proper curves round into each occipital lobe and is known as the forceps
major.

The septum lucidum (fig. 91, sept. Inc.}, a thin double partition, separates the
anterior part of the two lateral ventricles. It is composed of two distinct laminae,
having an interval between them (ventricle of the septum) which contains fluid
probably of the nature of lymph. It occupies the interval between tho corpus
callosum above and in front, and the anterior part of the fornix behind (fig. 91) ;
and gradually tapers backwards to end over the middle of the third ventricle, from
which it is separated by the fornix and velum interpositum. Antero-inferiorly it
extends downwards in an angle which reaches the anterior commissure.

The laminae of the septum are formed of a part of the mesial wall of the hemi-
spheres which has remained free, while the surrounding parts have become united
by the development of the corpus callosum above and in front and the fornix
below and behind. The ventricle of the septum was therefore originally a part of
the great longitudinal fissure, and has no connection with the internal ventricular
cavity of the brain. Accordingly we find that it is not lined by ciliated epithelium,
but each lamina consists of a thin layer of grey matter next to the cavity, and
homologous with the grey matter of the cerebral cortex, and a thicker layer of
white matter continuous below on either side with the general white matter of
the hemisphere. Externally, next to the lateral ventricle, is a layer of ependyma,
and covering this the epithelium which lines the lateral ventricle ; internally is a
layer of connective tissue, homologous with the pia mater.

The fornix (fig. 91, /) is an arched longitudinal white tract consisting of two
lateral halves, which are separated from each other in front and behind, but in the
intermediate part are joined together in the median plane. The two parts in front
form the anterior pillars (columnce fornicis} ; the middle conjoined part is named the
body ,• and the hind parts, which are again separated from each other, form the
posterior pillars (crurafornicis).

The body of the fornix is triangular in shape, being broad and flattened behind,
where it is adherent to the under surface of the callosum, and narrower in front,
where it is attached to the septum lucidum. Its lateral edges are free and are seen
projecting into the lateral ventricles just above the choroid plexuses. Its under
surface rests upon the velum interpositum, which separates it from the optic thalami
and the third ventricle (fig. 94).

Beevor distinguishes (in the monkey) two sets of fibres in the body of the fomix. Of
these, the mesial set, when traced backwards, appear to turn dorsally and pierce the corpus
callosum just in front of the splenium ; above the corpus callosum they may perhaps join the
posterior fibres of the cingulum (see p. 158), but their actual destination has not been certainly
followed out.

The anterior pillars (fig. 82, Cf}, cylindrical in form, can be traced downwards,
slightly separated from each other, in front of the foramina of Monro, of which
they form the anterior boundaries, and through the grey matter on the sides of the
third ventricle, curving backwards to the corpora albicantia. There each column
turns upon itself, making a twisted loop which forms the white portion of the
corpus albicans, and from this it appears to be continued, as the bundle of Vicq-
ffAzyr, upwards into the anterior nucleus of the optic thalamus (fig. 93). Each
pillar is connected near the foramen of Monro with the stria pinealis (taenia
fornicis), and with the taenia semicircular is, and it gives fibres to the septum
lucidum (for other connections of the anterior pillar, see p. 158).

According to the experiments of Gudden and Fore! the fibres of the anterior

130

THE FORNIX.

pillars find a termination in the grey matter of the corpora albicantia, and are not
directly continuous, as in dissected preparations they seem to be, with the bundle of
Vicq-d'Azyr.

The posterior pillars or crura of the fornix (fig. 94, 13} are the diverging
posterior prolongations of the two flat lateral bands composing the body. At first

sure ; co.m, middle commissure ; c/i, chiasma
quadrigemina ; ay, aqueduct.

Fig. 93. — SKETCH SHOWING THE ORIGIN AND CON-
NECTIONS OF THE ANTERIOR PILLARS OP THE
FORNIX. (Schwalbe.)

A median section has been made through the
third ventricle, and the superficial grey matter re-
moved at its anterior and lower part as far as a.
tli.s, upper part of the thalamus ; th.m, its mesial
surface : between the two is the medullary stria,
leading from the pineal gland and trigomim habenulse,
tr.h, to the anterior pillar of the fornix, c.f; f,
bundle of Yicq-d'Azyr ; c.m, corpus mamillare ;
i.f, fibres of the inferior peduncle of the thalamus
diverging in its substance ; co.a, anterior commis-
i, inf undibulum ; r.p, stalk of pineal body ; qu, corpora

they adhere to the under surface of the corpus callosum, then, curving outwards and
downwards over the pulvinar of the optic thalamus, each crus enters the'descending
horn of the lateral ventricle, where some of. its fibres are distributed on the surface of

Fig. 94. — VIEW OF THE UPPER SUR-
FACE OF THE VELUM INTERPOSITUM,
CHOROID PLEXUSES, AND CORPORA

STRIATA. (From Sappey after Vicq-
d'Azyr.) |

1 , fore part of the tela choroidea
or velum interpositum ; 2, 2, choroid
plexus ; 3, 3, left vein of Galen partly
covered by the right ; 4, anterior
pillars of the fornix divided in front
of the foramen of Monro ; on either
side are seen small veins from the
front of the corpus callosum and the
septum lucidum ; 5, vein of the
corpus striatum ; 6, convoluted
marginal vein of the choroid plexus ;
7, vein rising from the thalamus opti-
cus and corpus striatum ; 8, vein
proceeding from the inferior cornu
and hippocampus major ; 9, one from
the posterior cornu ; 11, fornix
divided near its middle and turned
backwards ; 12, lyra ; 13, posterior
pillar of the fornix ; 14, thesplenium
of the corpus callosum.

the great hippocampus and
the remainder are prolonged
as the narrow band of white
matter known as the tmnia
hippocampi or fimbria (fig.
89,^).

On examining the under

surface of the conjoined posterior parts of the fornix and corpus callosum, the
splenium of the latter with its thickened edge and the diverging halves of the
fornix appear to enclose between them a triangular structure, marked with trans-
verse, longitudinal, and oblique lines. To this part the term lyra has been applied

THE CORPUS STEIATUM.

131

(fig. 94, 12}. This contains a few fibres which pass across from one posterior pillar
of the fornix into the other, and are considered to form a commissural connexion
between the two hippocampal regions of opposite sides. This connexion is denied
by Beevor (in the monkey).

The taenia semicircularis is a band of white matter which lies in the groove
separating the ventricular surface of the nucleus caudatus from that of the optic
thalamus. It extends from the extremity of the descending horn of the lateral
ventricle, where it passes into the nucleus amygdalae, to the anterior part of the
body of the ventricle, as far as the foramen of Monro, having a curved course corre-
sponding with that of the ventricle. Its anterior connexions are somewhat obscure,
but, according to Schwalbe and Testut, it divides anteriorly into two parts, one of
which is continued into the anterior pillar of the fornix, and the other passes over
and in front of the anterior commissure to become lost in the grey matter which

Fig. 95. — CORONAL SECTION

THROUGH THE BRAIN AND
SKULL MADE WHILST FROZEN.

(Key and Retzius.)

c, c, corpus callosum ; below its
middle part the septum lucid um,
and below that again the fornix ;
L V, lateral ventricle ; th, thala-
mus ; between the two thalami
the third ventricle is seen ; below
the thalamus is the substantia
innominata ; str, lenticular nu-
cleus of the corpus striatum ;
c, caudate nucleus of the same ;
between th and str is the internal
capsule ; outside str is the thin
grey band of the claustrum, and
outside this again the island of
Reil at the bottom of the Sylviau
fissure ; n, a, nucleus amygdalae ;
immediately within this is the
optic tract seen in section ; p,
pituitary body ; B, body of the
sphenoid bone ; sa, subarachnoid
space ; v, villi of the arachnoid.

intervenes between the septum lucidum and the anterior end of the nucleus
caudatus : some fibres perhaps penetrating into that nucleus. According to Foville,
each extremity is ultimately traceable into the anterior perforated space.

The corpora striata (ganglia of the cerebral hemispheres), situated in front and
to the outer side of the optic thalami, are two large ovoid masses of grey matter, the
greater part of each of which is embedded in the white substance of the hemisphere
(extraventricular portion), whilst a part becomes visible in the body and anterior
horn of the lateral ventricle (intraventricular portion). The corpus striatum derives
its name from the streaked appearance it presents, especially in its anterior part,
when cut into, an appearance which is due to the passage through it of bundles of
white fibres of the internal capsule to the frontal lobe of the hemisphere.

The nucleus caudatus (intraventricular portion of the corpus striatum} (fig. 82,
Cs. ; fig. 88, c.str.), is of pyriform shape, its larger end being turned forwards and
appearing in the floor and partly in the lateral wall of the anterior horn. This
enlarged anterior extremity projects into the white matter of the frontal lobe, where
it is bounded by the fibres which pass from the genu of the callosum. Its narrow
end is prolonged backwards and outwards along the body of the ventricle and into
the roof of the descending horn, passing nearly to the extremity of the latter. The
caudate nucleus is separated from the thalamus by the tania semicircularis. Where

it lies in the lateral ventricle (superior surface) the nucleus caudatus is covered by a

K 2

132

THE CORPUS STRIATUM.

layer of ependyma and over this by the ciliated ventricular epithelium. The ganglion
is itself composed of a reddish grey substance like that of the outer zone of the
lenticular nucleus (see below). On the deeper side, that turned towards the internal
capsule, the nucleus receives from this a number of bundles of medullated fibres
which are^traceable from the crusta. According to Wernicke it is doubtful if any of
these pass on to the white matter of the hemispheres, nor do they come from the

Fig. 96. — VIEW FROM BEHIND OF A FRONTAL SECTION OF THE HEMISPHERES PASSING THROUGH THE
GENU OF THE CORPUS CALLOSUM. (E. A. S. ) From a photograph.

g.c.c., genu corporis callosi ; c.a., cornu auterius of lateral ventricle bounded laterally by the grey
mass of the corpus striatum ; cl., claustrum ; I.R., insula ; Sy., Sylvian fissure ; c-m.s., sulcus calloso-
marginalis; s.f.s., sulcus frontalis superior; s.f.i., sulcus precentralis ; s.olf., sulcus olfactorius ;
fr.orb., orbital surface of frontal lobe ; tr.olf., tractus olfactorius in section.

The section passes a little more anteriorly through the left hemisphere than through the right.

crusta directly, but only after traversing the medullary laminge of the lenticular
nucleus (see below).

The nerve-cells of the nucleus caudatus are multipolar, and, in the adult, pig-
mented. Some are moderately large, but most small, belonging to Golgi's second
type, with short axis-cylinder process (Marchi). Their nerve-processes pass in
various directions, some into the internal capsule. In addition, peculiar spheroidal
cells containing two or more nuclei were described by Henle.

The nucleus lenticttlaris (exlraventricular portion of the corpus striatum) is
separated in the greater part of its extent from the intraventricular part by a layer

THE CORPUS STRIATDM.

L33

of white substance (internal capsule), but is united with it in front, where it is
pierced, as just stated, by the fibres passing to the frontal lobe. The lenticular
nucleus is only seen in sections of the hemisphere. Its horizontal section (fig. 99, n.l)

Fig. 97. VIEW FROM BEHIND OF A FRONTAL SECTION OF THE HEMISPHERES PASSING THROUGH THE

MIDDLE OF THE ANTERIOR COMMISSURE. (E. A. S. ) From a photograph.

c.c., corpus callosum ; fo., anterior pillars of the fornix with the anterior extremity of the third
ventricle between them ; v.l. , lateral ventricles ; a. c. , anterior commissure ; n. c. , nucleus caudatus ;
gl,p., globus pallidus and pu., putamen, of nucleus lenticularis ; c.i., between the nucleus caudatus
and nucleus lenticularis, the internal capsule; cl., claustrum ; i. R., insula ; c. m.s., sulcus calloso-
marginalis ; s.fr.s., sulcus frontalis superior; s.pr.s., sulcus precentralis superior; tr.nlf., tractus
olfactorius passing to the anterior perforated space and giving off its mesial, lateral, and middle roots.

somewhat resembles that of a biconvex lens, being wider in the centre than at either
end, but larger anteriorly than posteriorly. It is less extensive than the caudate
nucleus, which projects beyond it at either end. The antero-posterior diameter
corresponds closely with that of the central lobe of the hemisphere, or island of Reil,
and the greatest width is opposite the anterior edge of the , optic thalamus. On a

134

THE CORPUS STRIATUM.

transverse vertical section through the middle (figs. 97 and 98), this nucleus appears
triangular, having a lateral, a mesial and an inferior surface, facing respectively the
external capsule, the internal capsule, and the base of the brain. Two white lines
(medullary lamina), parallel to the lateral border, divide it into three zones, of
-which the outer (putamen, Burdach, figs. 97, 98, pu.} is the largest and of a dark

Fig. 98. — VIEW FROM BEHIND OF A FRONTAL SECTION THROUGH THE RIGHT HEMISPHERE TAKEN JUST
BEHIND THE OPTIC CHiASMA. (E. A. S. ) From a photograph.

c.c. , corpus callosum ; /o., body of fornix : ///., third ventricle ; v.l., lateral ventricle ; n.c., nuclei!.;
caudatus ; str.m., stria medullaris ; ih., thalamus ; c.i., internal capsule ; ffl.p., globus pallidus ; pu.,
putamen ; c.e., external capsule ; cl., claustrum ; i.R., insula ; n.ainyy., nucleus amygdalae ; A, anterior
end of hippocampus major projecting into the descending cornu of the lateral ventricle ; tr. , optic tract ;
ch., optic chiasma ; n.opt., optic nerve ; c-m.s., callosotnarginal sulcus; Ro.s., Rolandic sulcus ; in-p.s.,
intraparietal sulcus ; Sy., Sylvian fissure ; pll.s., parallel fissure ; inf.t.s., second temporal sulcus ;
coll. s. , collateral sulcus.

reddish colour marked with fine radiating white striae, whilst the inner two, known
conjointly as the globus pallidus (gl.p.}, are yellowish in tint. On its outer side is a
grey lamina, termed the claustrum (cl.*), which is separated from the lenticular nucleus
by the stratum of white substance named the external capsule (c.e.). The internal
capsule (continuation of the crusta) separates it in the greater part of its extent
from the caudate nucleus and thalamus, but anteriorly the two nuclei of the corpus
striatum are united at their bases. Where it is widest (fig. 97) the lenticular

THE CORPUS STKIATUM.

135

nucleus is continuous below with the superficial grey matter forming the anterior
perforated lamina, into which the base of the claustrum also passes, and further
back it comes in contact below with the nucleus amygdalae (fig. 98) ; through
these structures it is continuous with the grey cortex of the hemisphere.

All three zones of the nucleus lenticularis are pervaded by bundles of white fibres,
but they are most conspicuous in the outer zone. The grey matter between the fibres
contains many cells with yellow pigment in them. The cells on the whole resemble
those of the caudate nucleus, but there are more in proportion belonging to the first
type of Golgi (cells with a long nerve-process). Fibres pass directly from the
inner zone into the adjacent part of the inner capsule (i.e., into the peduncle of the
cerebrum), while others from the substantia innominata below the optic thalamus.

Fig. 99. — HORIZONTAL SECTION THROUGH PART OP

THE CEREBRAL HEMISPHERE. (E. A. S. , after a

preparation by Mr. S. G. Shattock.) Natural size.1

The section is viewed from below ; v.l, lateral
ventricle, anterior cornu ; c.c, corpus callosum ;
s.l, septum lucidum ; «../, anterior pillars of the
fornix ; v 3, third ventricle ; th, thalamus opticus ;
st, stria terminalis ; c, nucleus caudatus, and n.l,
nucleus lenticularis of the corpus striatum ; i. c, in-
ternal capsule ; g, its angle or genii ; n.c, tail of the
nucleus caudatus appearing in the descending cornu
of the lateral ventricle ; cl, claustrum ; /, island of
Reil.

curve outwards around the mesial edge of
the peduncle and enter the lower part of
the lenticular nucleus as a distinct bundle
(ansa lenticularis, p. 112) and passing into
its medullary laminae are distributed in the
middle and outer zones.

Other fibres connect the caudate with
the lenticular nucleus, and others again pass
from this nucleus into the corona radiata
or white substance of the hemispheres and
thence to the cortex, but few fibres emerge
from or enter the lateral surface of the
lenticular nucleus, which is sharply marked i__
off from the external capsule.

The external capsule is formed of fibres which are not directly connected with
the lenticular nucleus but are derived partly from the anterior commissure, and in
part from a portion of the ansa lenticularis.

The claustrum (figs. 96 to 100, cl) is a thin lamina of grey matter which is smooth
next to the outer capsule but ridged and furrowed externally, the ridges and furrows
corresponding to the gyri and sulci of the central lobe, with the white substance of
which the claustrum is in immediate relation. According to Meynert the claustrum
is to be looked upon as a separated part of the grey cortex of the central lobe. In
transverse sections of the hemisphere the claustrum is seen to taper to a fine thread
superiorly (apex) and to expand below (base), having the shape of an elongated
triangle.

In the claustrum the cells are for the most part small and spindle-shaped, and
arranged parallel with the surface, resembling those which are met with in the

1 This figure shows the narrowed connections of the island of Reil with the rest of the hemisphere
(mantle). These narrow connecting parts have been termed by Gruldberg isthmi (anterior et posterior)
lobi centralis.

136

THE INTERNAL CAPSULE.

deepest layer of the grey cortex of the hemispheres. Most of the cells contain
yellow pigment.

The internal capsule (Burdach) (figs. 97 to 100, c.i. and i.e.') is a lamellated
tract of white fibres which lies between the nucleus lenticularis laterally and the
nucleus caudatus, stria terminalis, and optic thalamus mesially. It is somewhat
interrupted, especially in front, by strands of grey matter which unite the caudate
and lenticular nuclei. In front, behind and above it is continuous with the white
substance of the hemispheres, its fibres diverging in a fan-like manner towards the
cortex (corona radiata of Reil). Below it passes directly into the crusta, of which it
is the immediate continuation. In horizontal sections (fig. 99) the internal capsule
shows a bend (genu) opposite the stria terminalis, the anterior third forming an angle
of about 120° with the posterior two- thirds ; these two parts are known as the ante-
rior and posterior segments respectively. In vertical sections (fig. 100) it appears
to take a straight course, upwards and outwards from the crus cerebri to the

Fig. 100. — SECTION ACROSS THE OPTIC

THALAMUS AND CORPUS STRIATUM
IN THE REGION OF THE MIDDLE

COMMISSURE. (E. A. S., after a
preparation by Mr. S. G. Shattock.)
Natural size.

th., thalamus ; a, e, i, its anterior,
external and internal nuclei respectively ;
iv, its latticed layer ; m.c., middle com-
missure ; above and below it is the cavity
of the third ventricle ; c.c., corpus callo-
sum ; f, fornix separated from the third
ventricle and thalamus by the velum
interpositum. In the middle of this are
seen the two veins of Galen and the
choroid plexuses of the third ventricle ;
and at its edges the choroid plexuses of
the lateral ventricles ; t.s., tsenia semi-

circularis ; cr. , forward prolongation of the crusta passing laterally into the internal capsule, i.e. ;
S.t.r., subthalamic prolongation of the tegmentum, consisting of (1) the dorsal layer, (2) the zona
incerta, and (3) the nucleus of Luys ; s.n., substantia nigra ; ii.c., nucleus caudatus of the corpus
striatum ; n.l., nucleus lenticularis ; e.c., external capsule ; cl., claustrum ; /, island of Reil.

corona radiata. It has been determined as the result of experimental observa-
tions in animals, and from pathological and clinical observations in man, that the
fibres which course in the middle third of the internal capsule (i.e., which are
opposite the globus pallidus of the lenticular nucleus) are connected with the part
of the cerebral cortex excitation of which gives rise to movements in the various
parts of the body (Rolandic region of cortex), whilst those of the anterior third
are connected with the prefrontal region, and»those of the posterior third with the
occipito-temporal region.

Besides these fibres which connect the cortex of the hemisphere with the crusta,
the internal capsule contains others derived from various sources, viz., from the
caudate and lenticular nuclei, the optic thalamus, and sub-thalamic region, and
also, through the corpus callosum, from the cortex of the opposite hemisphere
(Hamilton). The exact localization within the internal capsule of most of these
fibres has not as yet been determined.

THE CEREBRAL HEMISPHERES. 137

EXTERNAL CONFORMATION OF THE CEREBRAL HEMISPHERES.

The cerebral hemispheres together form an ovoid mass, flattened on its under
side, and placed in the cranium with its smaller end forwards, its greatest width
being opposite to the parietal eminences. The hemispheres are separated in a large
part of their extent by a deep fissure, the great longitudinal fissure. On opening
this fissure by drawing asunder the two hemispheres, it is seen, both before and
behind, to pass quite through to the base of the cerebrum ; but for 10 centimeters
in the middle it is interrupted at a depth of about 30 mm. at the front to 40 mm.
at the back by a large transverse mass of white substance, named the corpus callosum,
which connects the two hemispheres together. While the brain is within the skull,
the longitudinal fissure is occupied by a vertical process of the dura mater — the falx
cerebri — which dips down between the two hemispheres, not quite reaching to the
corpus callosum in front but touching it behind.

Each cerebral hemisphere has an outer, convex surface, in contact with the vault
of the cranium ; an inner or mesial, flat surface, which forms one side of the
longitudinal fissure ; and an irregular under surface, in which is a deep cleft, the
vallecula Sylvii. In front of this cleft the under surface (orbital division) rests in
the anterior fossa of the base of the skull, behind it in the middle fossa (temporal
division), and further back still, on the tentorium cerebelli (occipital division). The
surfaces pass into one another at the borders, which are also three in number, viz. :
two mesial (superior and inferior) and one lateral. The anterior extremity of each
hemisphere is known as the frontal pole, the posterior as the occipital pole.

The surface of the hemispheres is composed of grey matter, and is moulded into
"numerous smooth and tortuous eminences, named convolutions or gyri, which are
marked off from each other by flssures or sulci of varying depth.

The convolutions are covered closely throughout by the vascular investing
membrane, the pia mater, which sends processes down to the bottom of the sulci
between them, while the arachnoid membrane passes from one convolution to another,
without dipping between them. In general, the height of a convolution exceeds its
width ; and its width at the surface is somewhat greater than at its base. The
convolutions present considerable variations of position, direction and complexity in
the brains of different individuals, and even in the two sides of the same brain, but
they are usually recognizable without much difficulty. It is far easier, however, to
trace the more important fissures and convolutions on the brain of a monkey, where
they are much less obscured by tortuosities and secondary sulci.

Since the external grey or cortical substance is continuous over the whole surface
of the cerebral hemispheres, being found alike within the sulci and upon the gyri, it
is obvious that a far greater extent of grey matter is thus provided for with a given
size of the brain, than could have been the case had the hemispheres been plain and
destitute of convolutions ; indeed, it is calculated that the extent of " sunken "
surface is twice that of " exposed" surface (cf. pp. 176, 177).

The sulci between the convolutions vary greatly in depth, being in some parts
quite shallow, in others as much as 25mm. (1 inch) or more deep. The average
depth is about 10mm. or 12mm. Certain well-marked sulci can easily be recognized,
and these serve as guides to the position of others which may at first be less readily
detected.

It may be well in the first instance to describe the six chief or " interlobar "
fissures, so-called because they are used to mark the hemisphere off into lobes ; ihe
lobes themselves, with the convolutions and fissures which are included within
them, can then conveniently be taken in order.

138

THE CEREBRAL HEMISPHERES.

Fig. 101.

THE CEREBRAL HEMISPHERES.

139

fig. 102.

140

THE CEREBRAL HEMISPHERES.

Fig. 103.

FISSURE OF SYLVIUS. 141

Fig. 101. — VlEW, FROM THE SIDE AND SLIGHTLY FROM ABOVE AND BEHIND, OF, THE RIGHT HEMISPHERE
OF A SIMPLY CONVOLUTED EUROPEAN BRAIN. (E. A. S. )

Fig 102. — MESIAL ASPECT OF THE LEFT HEMISPHERE OF A SIMPLY CONVOLUTED EUROPEAN BRAIN.

(E. A. S.)

Fig. 103. — UNDER SURFACE OF A SIMPLY CONVOLUTED EUROPEAN BRAIN. (E. A. S.)

The above are depicted nearly of the natural size. They have been drawn from photographs, and are
all taken from different specimens.

The sulci are marked with small italic letters ; the gyri with italic capitals. The corresponding
parts are marked similarly in the three figures,

Fig. 101. — Sulci — Ro., Rolandic or central; g, its superior genu ; Sy. a, anterior limb of Sylvian
(x, ascending part, y, horizontal part) ; Sy. p, posterior limb of Sylvian ; Sy. p. asp., ascending ramus
of posterior limb ; /1} superior frontal ; /2, inferior frontal ; /3, middle frontal ; /4, paramesial frontal ;
d, diagonal, placed in this instance rather low down, and communicating with the Sylvian ; p.o. ir>f,
inferior precentral ; p. c. i. ant. , its anterior ramus ; p. c. sup. , superior precentral ; p. c. m , mesial precentral ;
p.fl. tr., transverse precentral ; rtc. tr., transverse retro-central ; i.-p. inf, intra-parietal, pars inferior
(inferior postcentral) ; i.-p. sup., intraparietal, pars superior (superior postcentral); i.-p. post. s. hor..
intraparietal, pars posterior seu horizontal! s ; i.p. j)ost., intraparietal, pars posterior (paroccipital of
Wilder); i.-p. pr. asc., an ascending branch of the intraparietal; p.-o., parieto-occipital ; occ. ant.,
anterior occipital ; occ . lat. , lateral occipital ; cole. , posterior end of calcarine ; t x , first temporal or
parallel; tl asc., its posterior ascending extremity, detached; <2, second temporal; tzasc., its
posterior ascending extremity joined to and apparently continuous with the first temporal.

Gyri — Flt Fn, F3, first, second and third (superior, middle, and inferior) frontal; a, posterior part
of third frontal ; b, middle part (pars triangularis) ; c, orbital part ; A.F., ascending frontal ; A. P.,
ascending parietal ; rl\, Tz, T3, first, second, and third temporal.

Fig. 102. — Sulci — Ro., upper end of Rolandic ; p.c.m., mesial precentral ; fs, mesial frontal ;
a.m., calloso-marginal ; pr. I., prelimbic (anterior end of calloso-marginal) ; pr. I. asc., an ascending
branch of the prelimbic ; pamcentr., paracentral (posterior end of calloso-marginal) ; p. I. , post-limbic ;
?v). rostral; ro. inf., inferior rostral; p.-o., parieto-occipital ; calc. ant., stem of calcarine; cole, post.,
posterior part of calcarine ; 1,2, 3, 4, places where annectent gyri occur in calcarine and parieto-occipital
fissures; tz, third temporal ; coll.. collateral or fourth temporal; h (placed on the fascia dentata) has
the hippocampal fissure just below it.

Gyri — Flt marginal part of first frontal; C, callosal (gyrus fornicatus) ; H, hippocampal; unc.,
its uncus ; 7i, dentate; T±, fourth temporal (fusiform lobule); T5, fifth temporal or infracalcarine
(lingual lobule).

c.c, corpus callosum ; spl., its splenium ; g, its genu ; r, its rostrum ; fo, fornix ; fi., fimbria.

Fig. 103. — Sulci — orb., orbital (sagittal rami) ; o.tr., transverse orbital ; olf., olfactory; £x, £2, t3,
first, second, and third temporal; coll. , collateral (fourth temporal) ; calc., calcarine.

Gyri — R, gyrus rectus ; 7\, T3, '1\, Ts, first, third, fourth and fifth temporal ; H, hippocampal ;
s. r. a. , substantia reticularis alba ; unc. , uncus.

cJi, chiasma ; s.p.a., substantia perforata antica ; i.e., tuber cinereum ; m, corpora mamillaria,
accidentally separated from one another in the preparation ; cr, crusta ; tin, tegmentum ; spl., splenium
of callosum.

Fissure of Sylvius. — The most distinct fissure in the adult brain, and also the
first one to make its appearance in the development of the embryo, is the fissure of
Sylvius. This deep and conspicuous fissure is seen at the base of the brain, opening
out as the vallecula Sylvii (Broca) on to the anterior perforated space. From this
origin the fissure passes transversely outwards to the lateral surface of the hemisphere,
where it presently gives off a short horizontal branch (about 2 centimeters long),
and a rather longer ascending branch (about 8 centimeters), the fissure being then
continued nearly horizontally as the posterior limb for a considerable distance (8 or 9
centimeters) obliquely backwards and upwards in the direction of the parieto-
occipital fissure, having a slightly curved course. It ends at about the junction of
the middle and posterior thirds of the lateral surface (midway from superior to
lateral border), usually by bifurcating, one branch passing obliquely upwards, the
other backwards and somewhat downwards. If the lips of the Sylvian fissure are
separated, the island of Reil is seen at the bottom of the sulcus. In section this
fissure, together with the limiting sulcus of the island, forms a T-shaped figure (fig. 95).
Its bounding convolutions are folded over the island of Reil, and the upper bounding
convolutions which belong partly to the parietal, partly to the frontal lobe, form the
operculum of Burdach.

142

THE CEREBRAL HEMISPHERES.

The anterior horizontal and anterior ascending limbs of the fissure subdivide this operculum
into three unequal parts, an upper or fronto-parietal (pars fronto-pai'ietalis), a middle or
frontal (pars triangularis, "cap" of Broca), and a lower or orbital (pars orbitalis) (fig. 101,
a, b, c~). All these are now often spoken of as opercula. The convolution bounding the
Sylvian fissure below is also spoken of as the temporal operculum, so that four opercula are
thus enumerated. They are formed in the embryo by the manner in which the mantle comes
to overlap the central lobe. The temporal and fronto-parietal appear first, above and below the
Sylvian fossa of the embryo : the frontal and orbital develope much later. The meeting of
the four opercula determines the formation of the three limbs of the Sylvian fissure (fig. 104).

The Sylvian fissure is usually longer in the left than in the right hemisphere ; the difference
being due to the greater development of the frontal operculum on the left side (fig. 106)

Fig, 104. — DIAGRAMS ILLUSTRATING THE MANNER IN WHICH THE INSULAR REGION is COVERED IN BY
THE VARIOUS OPERCULA. (Cunningham.)

The part printed black represents uncovered part of the Sylvian fossa of the embryo, the unshaded
portions represent the different opercula.

P.P., fronto-parietal operculum ; T., temporal operculum ; F., frontal operculum (pars triangularis
of third frontal gyrus) ; 0, orbital operculum ; p. h., posterior limb of fissure ; a. a., anterior ascending
limb ; aji., anterior horizontal limb.

In I, the fronto-parietal and temporal opercula are beginning to grow over the fossa ; in II, the
formation of all four opercula is advanced, the pars triangularis being well marked, and the anterior
limb U-shaped. In III, the pars triangularis is only slightly developed, and the anterior limb is a Y ;
in IV the pars triangularis is absent and the anterior limb is simple (I-form).

(localisation of speech centre, Broca). The horizontal and ascending limbs of the anterior
branch of the Sylvian fissure often arise from a common stem (Y-condition, fig. 101 and fig.
106, right side), the pars triangularis being then less developed than usual. This part may
even not form a distinct opercular projection, in which case the anterior limb of the Sylvian
fissure is undivided (I-condition).

The anterior and ascending limbs arose by a common stem from the main fissure (Y form),
in 32 p. c. of the hemispheres examined by Cunningham ; independently (V and U form) in
37 '5 p. c. ; and as a single limb (I form) in 30 p. c. There are sometimes two secondary
extensions of the Sylvian fissure on to the orbital lobe (orbital limbs), but these are less deep
and have not the same morphological importance as the others.

The posterior limb about corresponds in the adult to the level of the squamous suture, but
in children younger than fifteen years it is rather above this level. The angle which the
direction of the posterior limb forms with a line perpendicular to the superior border of the
hemisphere (Sylvian angle), varies considerably, but is more acute on the whole in the child
than in the adult (Cunningham).

In the brain of some monkeys, the posterior limb of the Sylvian fissure joins (superficially)
the parallel fissure, which it gradually approaches, and the two are continued as an apparently

PARIETO-OCCIPITAL FISSURE. 143

conjoined fissure almost as far as the upper margin of the hemisphere ; this conjunction is
sometimes found in the human subject.

Fissure of Rolando. — The fissure of Rolando,1 or central sulcus (Huschke)
(fig. 101, Ro. ; and figs. 105, 107 (monkey) ), extends across the lateral convex surface
of the hemisphere interrupting the general longitudinal course of the gyri and sulci.
The parallel convolutions which bound it are named respectively the ascending
frontal and ascending parietal convolution or the central gyri. It begins above, near
the vertex or highest point of the hemisphere, somewhat behind the middle of
the great longitudinal fissure, and passes downwards and forwards to end near
the middle of the fissure of Sylvius, the posterior limb of which it sometimes (but
rarely) joins. The junction is effected by the medium of a small sulcus, precenlral
transverse sulcus (figs. 101, 106, p. c. tr.\ the inferior transverse sulcus of Eberstaller,
which is usually separated from the lower end of the Rolandic fissure by an annectent
gyrus joining the two central convolutions. The Rolandic fissure usually reaches
the superior border of the hemisphere, but sometimes stops short of that line ; it
often exhibits a hook -like backward inclination at this extremity. As just mentioned,
it passes obliquely downwards and forwards, but not in a perfectly straight course,
for it has certain well-marked curves. At about the junction of its upper and middle
thirds it is generally curved with the concavity forwards ; just below its middle
third it has a second bend with the concavity backwards, while in the lowest part its
direction is nearly vertical, with a tendency of the lowermost end to curve backwards.
The upper curve sometimes forms a very distinct bend (superior genu, fig. 101, #),
representing a deep bay which is here found in the brain of the anthropoid apes (fig.
105). The middle part of the fissure is then nearly horizontal. It is very rarely
interrupted in its course, although on separating its lips it may often be seen that
there is a tendency to the appearance of an annectent gyrus about the level of the
superior geiiu, and it is here that the interruption is liable to occur. The fissure
of Rolando appears early (end of fifth month), being laid down in two parts, an
upper shorter, and a lower longer portion (Cunningham). In this double mode of
origin it resembles the precentral and postcentral sulci.

The acute angle which the slope of the fissure of Rolando forms with the superior border
of the hemisphere is known as the Rolandic angle. According to Cunningham it averages
71*7°. The two Rolandic fissures form therefore when looked at from above, a wide V, open
forwards and forming an angle of 143°. The length of the fissure is about |ths of the whole
length of the hemisphere. It is relatively longer and more curved in the anthropoid apes than
in man.

This fissure has once been found duplicated, the two fissures replacing it being separated
by a gyrus (g. Rolandicus) along their whole length (Griacomini). The condition was present
in both hemispheres of the same brain.

Parieto-occipital fissure. — The parieto-occiintal fissure is best marked on the
mesial surface of the hemisphere, where it appears as a deep cleft (fig. 102, p.-o.),
extending downwards and a little forwards from the margin of this surface to near
the posterior extremity of the corpus callosum, where it usually joins the calcarine
fissure, the two together forming a Y which encloses a wedge-shaped portion of the
occipital lobe (cuneus). On the convex surface the fissure is continued transversely
outwards for a variable distance, generally only a few millimeters (external part of
the parieto-occipital fissure (fig. 101, p.-o.} ). This fissure is here taken as the division
between the parietal and occipital lobes. The size of its external portion depends
(inversely) on the size of the annectent gyrus which curves round its outer extremity
and connects the parietal with the occipital lobe. In Quadrumana (figs. 105, 107) the
external portion of this fissure is concealed within a deep transverse cleft (Affenspalte)

1 Although thus named by Leuret (Anatomie compares du systeme nerveux, 1839), from attention
having been directed to it by Rolando a few years previously, this fissure was noticed and figured by Vicq-
d'Azyr (Traite' d'anatomie et de physiologic, 1796).

144

THE CEREBRAL HEMISPHERES.

which intervenes between the parietal and occipital lobes, the cleft tending obliquely
backwards, so that the occipital edge somewhat overlaps the parietal (occipital
operculum). This " Affenspalte ," is not represented in the adult human brain, but it
is apparently represented by a temporary fissure which is seen in the foetus during the
fifth and sixth months (external perpendicular fissure of Bischoff).1 The parieto-
occipital fissure appears about the fourth or fifth month on the mesial surface. It is
about on a level with the lambda (see Vol. II., p. 83), or a little in front of the
level of that spot : more so in the child than in the adult (Cunningham).

The calcariue fissure (Huxley). — This is seen on the mesial surface of -the
hemisphere (fig. 102). It is a deep fissure, extending from near the posterior

RuvL.

.peer. oc.f.

Pr.L

Oc.L,.

Fig.105. — BRAIN OPCHIMPANZEE.
(From Gratiolet.)

Fr. L. . frontal lobe ; Par. L. ,
parietal lobe : Oc.L., occipital
lobe ; Temp. Sph. L., temporo-
sphenoklal lobe ; Sylv. /., fissure
of Sylvius ; f.Sy.a., f.Sy. p., its
anterior and posterior limbs ; .
f. Rol., fissure of Rolando ;
tr. fr. f., transverse frontal (pre-
central) fissure ; int. par. f., in-
tra parietal fissure ; par. oc. f.,
parieto-occipital fissure.

extremity of the brain.

where it usually begins in

a T-shaped fork, in a course curved at first upwards and then downwards, and
ending below the splenium of tfie corpus callosum. The forked posterior extremity
near the occipital lobe is sometimes cut off from the rest of the fissure, and appears
as an independent sulcus (sulcus extremus of Schwalbe). In many Quadrumana the
anterior extremity appears to be continued into the hippocampal fissure, but this is
usually superficial only, and occurs but rarely in the human brain.

The anterior part of the calcarine fissure is by far the deepest part, and it is this part
which indents the posterior horn of the lateral ventricle and forms the calcar avis. A short
distance from its anterior extremity the calcarine receives the internal parieto-occipital
fissure, although in the depth of the latter fissure there is usually a small gyrus, passing from
the apex of the cuneus to the isthmus of the gyrus fornicatus (opposite 1. fig. 102) (cuneo-
limbic annectent gyrux). This sometimes comes to the surface and shuts off the continuity
of the two fissures, which otherwise form a Y-shaped figure, the stem of the Y being formed
by the anterior part of the calcarine, the limbs by the parieto-occipital and posterior part of
the calcarine respectively. This posterior part of the calcarine is developed independently of
the stem, which is a direct representative of one of the total fissures of the foetal hemisphere,
while the posterior part of the calcarine (posterior calcarine of Cunningham) is formed much
later by two depressions, which ultimately run together and into the true calcarine. The
original independence of these parts is indicated by the existence of two annectent gyri
(anterior and posterior cunco-linrjuar) concealed within the posterior part of the calcarine :
one at its junction with the stem of the Y, and the other near the hinder end. The places of
these annectent gyri are indicated by 2 and 3 in fig. 102.

The parieto-occipital fissure is frequently interrupted in its depth by two annectent gyri.
One of these is the cuneo-limbic annectent gyrus already mentioned (fig. 102, 1), the other,
placed higher, may be termed the cnneo-qnadrate annectent (fig. 102, at 4).

The parieto-occipital is preceded in the foetus by a fissure occupying about the same situa-
tion, but this usually disappears before the permanent fissure makes its appearance.

The collateral fissure (Huxley). — This is seen on the inferior surface, where
it lies below and parallel to the anterior part of the calcarine (figs. 102, 103, coll.}.
It extends forwards towards the tip of the temporal lobe, but does not reach the

1 According to some authorities, the anterior occipital sulcus of the adult brain (see p. 152) repre-
sents the Affenspalte of Quadrumana.

THE FRONTAL LOBE. 145

extremity of the lobe. The middle part of this fissure, which mainly causes the
projection of the collateral eminence in the lateral ventricle (see p. 125), is formed
independently of the two extremities.

The calloso-margiiial fissure (Huxley) is an extensive fissure of the mesial
surface, which begins below the rostrum of the corpus callosum close to the anterior
perforated space, and sweeping round the genu of the callosum runs parallel to that
body, separated from it by the gyrus fornicatus, as far as a little behind the middle
of the hemisphere, where it turns obliquely upwards, and ends at the upper margin
of the hemisphere a short distance behind the commencement of the fissure of
Kolando (fig. 102). Both the anterior and the posterior parts of this fissure are deve-
loped independently of and are often permanently distinct from the middle part.
The anterior part or pretimbic fissure (fig. 102, pr.-l.} sweeps round the genu of the
corpus callosum, and when distinct from the middle part passes obliquely upwards
towards the upper margin of the hemisphere. In any case it usually sends a well-
marked ascending branch towards the margin (fig. 102, pr.-l. asc.). The posterior
part of the calloso-marginal (paracentral fissure of Wilder, fig. 102) hooks round the
inflected end of the fissure of Rolando, and is curved round the paracentral lobule,
which it bounds behind, below, and in front : the last by an ascending ramus, which
comes off at the junction of the posterior with the middle part of the calloso-
marginal fissure.

The six fissures which have been described are used by anatomists to map out the surface
of the brain into regions to which the name of " lobes " has, not very appropriately, been
applied. In all, seven lobes are enumerated, viz., the frontal, parietal, occipital, temporal,
and liniMc, the island of Re,il, or central lobe, and the olfactory bulb and tract, or olfactory
lobe. It must, however, be understood that these so-called lobes have by no means an equal
morphological value, nor do they correspond precisely with the functional differentiations
of the hemisphere which can be made out as the result of experiments on animals, and
c-linical and pathological observations in man.1 The distinction is further artificial because
the so-called lobes are in many places not marked off from one another otherwise than by
imaginary lines. Nevertheless it is found convenient for purposes of anatomical description
to consider the surface of the brain as thus constituted, and they will accordingly be here
described in the order in which they have been above enumerated.

THE FRONTAL LOBE. — The fissure of Rolando, passing obliquely down-
wards from the upper margin of the brain towards the Sylvian fissure, marks off the
anterior part of the hemisphere — constituting in man nearly one-third of the whole —
as the frontal lobe. This term, however, includes not only the part of the external
surface which is thus marked off, but the corresponding adjacent part (marginal con-
volution) of the mesial surface, as far as the calloso-marginal fissure, and also the
under or orbital surface of this anterior part of the brain. In the description of the
fissures and convolutions within the lobe, these three surfaces will be separately
considered.

SULCI AND GYEI OF THE ExTEKNAL SURFACE. — The precentral sulctis
(pre-Rolandic sulcus of Broca) (fig. 101, p.c.inf.,p.c.sup. and p.c.m.) has a direction
parallel with that of the fissure of Rolando, from which it is separated by
the ascending frontal gyrus. It is sometimes complete, but more usually is
subdivided into two or three separate portions by annectent gyri, which connect
the ascending frontal with the superior and middle frontal respectively ; a third
annectent gyrus passes below the lower end of the fissure, and unites the ascending
frontal with the third frontal. The uppermost portion (sulcus precentralis mesialis,
fig. 101, p.c.m,.} cuts the upper border of the hemisphere, and appears on the
mesial surface (fig. 102, p.c.m.} often as a well-marked vertical fissure, which

1 Certain of them it is true, such as the olfactory and the occipital lobe and to a less marked degree
the temporal lobe, appear to have a localized association with the functions of certain special sense
organs.

VOL. III. L

146 THE CEREBRAL HEMISPHERES.

occasionally runs into the calloso-marginal, to which it has sometimes been regarded
as belonging (Schwalbe '). The next portion (sulcus precentralis superior), is very
often continued forwards into the first frontal sulcus (/„ fig. 101). Its middle part is
opposite the upper genu of the fissure of Kolando. The inferior portion (sulcus
precentralis inferior} is by far the best marked. It separates the ascending frontal
from the third frontal gyrus, and usually gives off a well-marked branch anteriorly
into the middle frontal gyrus (which may, as in fig. 101, p.c.i.ant., be the main
continuation of the fissure). After giving off this branch the fissure is usually pro-
longed upwards for some distance, but this is not shown in the brain figured, where
the superior precentral extends unusually low down. The inferior precentral sulcus is
often joined to the Sylvian fissure, either directly or through the intermediation
of the sulcus precentralis transversus (see p. 143), or of the sulcus diagonalis (see
p. 148), but there is usually, perhaps invariably, an annectent gyrus concealed in
the depth, of .the fissure even in these cases. The inferior frontal sulcus sometimes
appears to spring from the inferior precentral, either near its middle, or, as in the
brain figured, from its anterior branch, but the two are probably more frequently
separated by an annectent gyrus which here joins the middle and inferior frontal gyri.

Two well-marked sagittal sulci (superior and inferior frontal) course over the
external surface of the frontal lobe in front of the precentral fissure ; they subdivide
this part of the lobe into three sagittal gyri, superior, middle and inferior. Besides
these constant sulci, there are certain others which are less constant in their
occurrence, and in the extent to which they are developed as connected fissures, viz.,
one running along the middle of the superior frontal gyrus, which we will term from
its position near the upper border, the paramesial sulcus (fig. 101, /4), (s. mesialis of
Cunningham), and one running along the centre of the middle frontal gyrus (sulcus
frontalis medius of Eberstaller), (fig. 101,/3). Both of these are not only inconstant
in their occurrence, but when present are frequently interrupted, and then appear to
consist of a series of separate parts, which are often united here and there with the
other frontal sulci.

The midfrontal sulcus (s. frontalis medius) usually bifurcates in front, and
becomes transverse (s. transversus anterior, frcnto-marginal sulcus of Wernicke).

The superior frontal sulcus (/i ) is developed after the inferior, and along with
the upper part of the precentral, with which it is usually in direct continuity. This
sulcus is often interrupted by superficial annectent gyri passing obliquely from before
backwards from the first to the second frontal convolution. Anteriorly, the superior
frontal often passes into the mid-frontal sulcus (Cunningham). This is the case in
the brain figured (fig. 101). Posteriorly, its line may be continued by a branch
from the superior precentral sulcus passing across the ascending frontal gyrus. This
was also the case in the brain here figured.

The inferior frontal sulcus (f.2 ) usually curves forwards from the middle of the
inferior precentral sulcus towards the frontal pole of the hemisphere. Several small
secondary furrows pass from it above and below, and it is sometimes subdivided by
superficial annectent gyri into three portions. Anteriorly it bifurcates, forming a
transverse piece, which may develop separately. At the apex of the lobe, in front
of and sometimes forming part of this fissure, are one or two transverse sulci
forming the sulcus radiatus and lateral fronto-marginal sulcus of Eberstaller.

Gyri. — Four convolutions are described upon this surface, three of which run
antero-posteriorly, while the fourth takes a direction obliquely across the brain, and
parallel with the fissure of Kolando. The three antero-posterior convolutions are
termed respectively the superior, middle and inferior, m first, second, and third frontal

1 Schwalbe has termed it the "sulcus paracentralis, " but this is not to be confounded with the
fissure to which that name has been given by Wilder (p. 145).

THE THIRD FRONTAL GYRUS.

147

gyri. They are separated from one another by the upper and lower longitudinal
frontal sulci, and from the fourth or ascending frontal gyrus by the precentral
sulcus, which runs parallel to the fissure of Rolando.

The first frontal gyrus (FJ, which is much the longest, runs parallel with the
upper margin of the hemisphere, over which it is continuous with the marginal con-
volution of the mesial surface, the two, in fact, really forming a single convolution to
which the name first frontal is frequently applied. This convolution reaches the frontal
pole of the hemisphere in front ; behind it is partly continued into the upper end
of the precentral or ascending frontal gyrus, partly separated from that gyrus by the
upper end of the precentral sulcus ; below it is marked off from the middle frontal
by the irregular and somewhat interrupted superior frontal sulcus. It is sometimes
subdivided by a longitudinally coursing sulcus (paramesial, s. frontalis mesialis of
Cunningham) into two parts, but less often than the second gyrus. This subdivision
is rarely found in the brain of the negro.

The second frontal gyrus (F.2), runs below and parallel to the first. It is
separated from the precentral by the precentral sulcus, the course of which is,
however, here usually interrupted by a well-marked annectent gyrus. The inferior
frontal sulcus separates it from the third gyrus. It is also often subdivided by a
longitudinally coursing sulcus (midfrontal sulcus) into two parts, an upper or lower,
which are sometimes described as distinct convolutions.

The third frontal gyrus (^3) the smallest of the three, is curved around both
the anterior and the ascending limbs of the Sylvian fissure, which deeply indent the

Left side.

Right side.

Fig. 106. — VIEWS OF THE THIRD FRONTAL GYRUS OF THE RIGHT AND LEFT HEMISPHERES OF THE SAME

BRAIN. NATURAL SIZE. FROM PHOTOGRAPHS. (R. A. S. )

/2, inferior frontal sulcus ; p.c. inf., lower end of inferior precentral, very short, and not lettered
on the left side, and continuous on the right side with, d, diagonal sulcus (on the left side d joins /,) ;
p.c. tr, transverse precentral ; Sij. a, anterior limb of Sylvian fissure ; x, ramus ascendens, y, ramus
horizontalis ; a, posterior part of third frontal (divided by the diagonal sulcus into two parts, viz., pars
basilaris behind, and pars ascendens in front) ; b, middle part of third frontal or pars triangularis,
partly subdivided on the left side by secondary sulci ; c, orbital part of third frontal.

gyrus, and subdivide it into three parts, anterior (pars orbitalis), middle (pars trian-
gularis), and posterior (pars basilaris). It is more developed on the left side of the
brain than on the right — correspondingly with the localization of the speech-centre
on the left side (Broca). This increased development chiefly affects the triangular
middle part which lies between the anterior and ascending limbs of the Sylvian
fissure (" cap " of Broca). "When well developed, the triangular part entirely separates
these two limbs (tig. 106, left side), when less marked, they are confluent below (fig.
106, right side); if the triangular part is abs'ent they are entirely confluent (see also
fig. 104 and p. 142). This inferior frontal gyrus is connected at its lower and

L 2

148

THE CEREBRAL HEMISPHERES.

posterior end by an annectent gyrus with the lower end of the precentral, while at
its anterior end it passes round to the orbital surface of the lobe.

This gyrus is usually regarded as being bounded posteriorly by the inferior
precentral sulcus, but it is,. for many reasons, more convenient to regard the trans-
verse precentral as the posterior limit.

It is occasionally subdivided into two by a longitudinal sulcus concentric with the inferior
frontal (Giacomini).

The pars basilaris is subdivided into two parts (anterior and posterior divisions) by an
oblique fissure, the sulcus diagonalis of Eberstaller (figs. 101, 106. d). This is usually distinct,
but sometimes joins the inferior precentral (fig. 106, right side), the inferior frontal (fig. 106,
left side), or even the Sylvian fissure. The last is the case in fig. 101. The pars triangularis
is also often scored by secondary sulci (figs. 101, 106).

According to most modern authorities the third frontal gyrus is almost or quite rudimentary
in all primates excepting man. Cunningham points out, however, that although it is true
that the opercular part of this convolution is not present in the apes, the same remark does
not apply to the non-opercular part, and he believes that the inferior frontal sulcus, which is

Fig. 107. — BRAIN OF MA-
CACQUE MONKEY. Natural
size. (E. A. S.)

Sulci. — A.-SJJ, "Affen-
spalte ; " i. -p, intraparietal ;
i.-p.si superior part of intra-
parietal ; Bo., Kolandic ;
Sy. j), Sylvian, posterior limb;
flt superior frontal; .?.?'., sul-
cus rectus (inferior frontal) ;
p. c. i, precentral inferior ;
•p.c.i.a., its anterior ram us ;
p.c. tr., transverse precen-
tral ; £1? parallel.

regarded by most authorities as not represented in the apes, is, in fact, represented in them by the
well-marked sagittal furrow (irulciis rectvg quadrumanorum, fig. 107, #.r.~) which runs forwards
from near the angle of the inferior precentral sulcus to the apex of the hemisphere. This view,
which was that taken by Gratiolet (Memoire sur les plis cerebraux de 1'homme et des primates,
1854), gives a well-developed third frontal gyrus to the ape brain, whereas if the sulcus in
question be regarded as the superior frontal (Schwalbe, Mingazzini), or as the sulcus frontalis
medius (Eberstaller, Herve) of the human brain, the sulcus frontalis inferior must be absent
in the ape, or at most represented by a small fronto-orbital sulcus which is sometimes
present at the lowermost limit of the lobe (see fig. 107). But the superior frontal sulcus of
man is represented in the monkey by one or more deep indentations of the cortex lying in a
sagittal line near the margin and sometimes partly confluent (fig. 107,/t), and in some apes
there is also a distinct mid-frontal sulcus besides the sulcus rectus : moreover, the study of
the development of the inferior frontal sulcus in man is also in favour of Gratiolet's view.
For a full discussion of this question the student is referred to Prof. D. J. Cunningham's
memoir, " The Surface Anatomy of the Primate Cerebrum," Dublin, 1892.

The anterior central, precentral, or ascending frontal gyrus (fig. 101,
A.F.) lies between the fissure of Rolando and the precentral sulcus, and extends from
the superior margin of the hemisphere (where it is continuous with the posterior
part of the marginal gyrus on the mesial surface) to the Sylvian fissure. It is
narrowest in the middle, enlarging somewhat above and below. It is usually con-
nected, as just mentioned, with each of- the three longitudinal frontal convolutions
by an annectent gyrus, the precentral sulcus being thereby considerably interrupted.
There is a similar connection by a curved annectent gyrus below the fissure of
Rolando, with the ascending parietal convolution.

SULCI AND GYKI OF THE MESIAL SURFACE. — On the mesial surface of the
hemisphere there is only one convolution which is considered to belong to the frontal
lobe, viz., the marginal gyrus (fig. 102, FJ. This, as above explained, is continuous
over the upper border with the superior longitudinal of the external surface. It is
separated from the callosal or fornicate gyrus of the limbic lobe by the calloso-marginal

PARIETAL LOBE. ]49

fissure, and is partially interrupted by the ascending branches of that fissure. Besides
these, there is often, but not constantly, a sagittal fissure running along the middle of
the convolution. This fissure (sukus frontalis mesialis s. marginalia) subdivides the
middle of the gyrus into superior and inferior parts. The antero-inferior part of
the marginal gyrus is marked by two or three sulci which are curved concentrically
with the prelimbic part of the calloso-marginal sulcus. These have been termed by
Eberstaller the rostral sulci (supra-orbital of Broca) (fig. 102, ro., ro. inf.) Below
the genu of the callosum the marginal gyrus is continuous with the limbic lobe
by one or more broad fronto-limbic annectent gyri. Other annectents are found
between the several parts of the calloso-marginal sulcus, when this is subdivided ;
when it is not subdivided they are concealed in its depth. At its posterior end the
marginal gyrus becomes continuous with the two central gyri on either side of the
upper extremity of the fissure of Rolando. But this posterior part of the marginal
gyrus is nearly cut off from the rest of the gyrus by the anterior ascending part of the
paracentral sulcus, and is distinguished as the paracentral or oval lobule (fig. 102).

SULCI AND GYRI OF THE ORBITAL SURFACE. — The orbital sulcus (H-shaped
sulcus, triradiate sulcus) is a complex of sulci, which extends over the greater part
of the flattened orbital surface of the frontal lobe. It consists of a posterior part
(sulcus orbitalis transversus of Weisbach, fig. 103, o.tr), which curves round from near
the anterior Sylvian fissure laterally, in an arch convex forwards, to end mesially
near the lateral root of the olfactory tract ; and of three or four sulci having a
general sagittal direction (sulci orbitales sagittales), and usually communicating
posteriorly with the transverse orbital. These sagittal sulci vary greatly in their
number and extent, and in the number and direction of the secondary and tertiary
sulci, which come off from them, and they frequently produce, with the transverse
sulcus, the figure of an H, K or X. Weisbach has endeavoured to connect these
variations with racial and sexual differences, but there does not seem to be any
foundation for such connexion, and in fact (as is well shown in fig. 103), two
entirely different types may be found on opposite hemispheres of the same brain.

Three convolutions are described as lying in front of the transverse orbital
sulcus, named, according to their position, the inner, middle, and outer orbital
gyri. The last of these is continuous at the side with the inferior frontal, the first
and second are the continuations of the superior and middle frontal convolutions.

On the inner gyrus is seen the olfactory sulcus (s.olf.) in which the olfactory
tract and bulb lie. It has a straight course nearly parallel with the great longitudinal
fissure, but somewhat inclining towards it. The part of the inner gyrus between
the olfactory sulcus and the mesial border is sometimes known as the gyrus rectus (R).
Behind the transverse orbital sulcus, between it and the anterior limiting sulcus of
the insula, is a fourth gyrus, the posterior orbital, which is also continuous with
the inferior frontal.

The continuity of the convolutions of the external with those of the orbital surface is often
interrupted by a sulcus which crosses their direction, extending across the front of the lobe
from the anterior end of the Sylvian (sulcus fronto-orbitalis, Griacomini ; fronto-marglnalls
lateralis, Eberstaller).

PAEIETAL LOBE. — This lobe lies behind the frontal, in front of the occipital,
and above the temporal lobe. It is bounded in front by the fissure of Rolando,
behind by the parieto-occipital and anterior occipital fissures (p. 152), laterally and
below by the posterior limb of the fissure of Sylvius as far as this preserves its
horizontal direction, and then by a line connecting this with the lower end of the
anterior occipital, but it is here freely continuous with the temporal lobe.. Above
and mesially it extends within the great longitudinal fissure and appears on the
mesial side of the hemisphere, as the quadrate lobule.

SULCI AND GYRI OF THE PARIETAL LOBE. — The intraparietal sulcus

150 THE CEREBRAL HEMISPHERES.

(Turner) (fig. 101) arches through the parietal lobe, commencing in its anterior
inferior angle, where it is sometimes, though rarely, continued into the fissure of
Sylvius. It ascends at first parallel to the fissure of Rolando (pars ascendent
inferior s. postcentralis inferior], and then turns backwards horizontally to the back
of the lobe (pars horizontalis s. posterior), extending nearly to the termination of
the parieto-occipital fissure, past which it is continued (pars occipitalis, paroccipital of
Wilder) to join the anterior occipital. Its horizontal portion divides the parietal lobe
into two parts, the superior and inferior parietal lobules, and it is frequently bridged
across by annectent convolutions connecting those lobules. One or two well-marked
rami pass into the superior parietal lobule from the upper side of the pars horizon-
talis, and as many shallow sulci extend from its lower concave side into the inferior
parietal lobule.

Above the pars ascendens inferior and often separated from it by an annectent
gyrus connecting the superior parietal lobule with the ascending parietal gyrus is a
short vertical fissure (postcentralis superior), which is termed by Cunningham the
pars ascendens superior, since in a large number of instances it is directly continuous
with the pars ascendens inferior (the bridging gyrus being then absent), and the
two conjoined parts then constitute a sulcus which runs parallel to the fissure of
Rolando, and is termed the postcentral sulcus (Ecker).

Although the condition with a detached pars ascendens superior is to be regarded as typical
of this sulcus as shown both by its occurrence in most of the Quadrumana and the course of
its development in the human embryo, it is by no means the most common in the adult
human brain, the most usual condition being that here figured (fig. 101) in which there is a
complete postcentral sulcus from which the horizontal arm passes off backwards at an oblique
angle towards the occipital lobe, although generally interrupted near the anterior limit of that
lobe by an annectent gyrus. An arrangement of this character was met with by Cunningham
in 56 p. c. of his cases. In 16 p. c. a more or less complete postcentral sulcus was present,
and was cut off from the horizontal part of the fissure by an annectent gyrus. Occasionally
the postcentral sulcus communicates above, and sometimes also below, with the fissure of
Rolando. Three deep annectent gyri partially interrupt the horizontal part of this fissure and
join the superior and inferior parietal lobules (Eberstaller) ; these have been supposed to be
a human characteristic, but they occur in the Chimpanzee and occasionally in the Baboon
(Cunningham).

In rare cases the pars ascendens inferior of this fissure is cut off from the pars horizontalis,
and the latter is continuous with the pars ascendens superior alone. In other and also rare
instances all the parts of the fissure are separated from one another by bridging convolutions,
so that the fissure appears as four distinct pai'ts, viz., the two portions of the postcentral
sulcus (lower and upper) , the pars horizontalis and the pars occipitalis.

The occipital continuation of the intraparietal fissure is sometimes separated from the
rest of the fissure (paroccipital fissure of Wilder). It usually terminates posteriorly by
joining a sulcus which is nearly vertical to its direction, the sulcus transversus occipitalis of
Ecker (sulcus occipitalw anterior, fig. 101). This will be further noticed in connection with
the occipital lobe. In the monkey's brain the occipital termination is concealed within the
deep cleft (Affenspalte) formed by the occipital operculum.

Below the postcentral sulcus and cutting into the margin of the f ronto-parietal operculum,
is a small oblique sulcus (*. retro-centralis transversus of Eberstaller) (fig. 101, rtc.tr.'). This
sometimes serves to prolong the intraparietal fissure into the fissure of Sylvius.

The intraparietal fissure is usually developed in the foetus in four segments (Cunningham),
which appear in the following order, viz., inferior postcentral. horizontal, occipital, and
superior postcentral. It is better developed, i.e., more continuous and deeper, in apes than in
man ; but the superior postcentral part is either not developed or is rudimentary in them
(fig. 107). The so-called horizontal part is not truly horizontal, but has an upward inclination
which is more marked in the male human brain than in the female.

The posterior central, postcentral, or ascending parietal convolution
(fig. 101, A. P.) lies behind the fissure of Rolando, between this and the postcentral
sulcus, and parallel to the ascending frontal convolution, with which it is usually
continuous below the fissure of Rolando. Above, it is connected by a broad annec-
tent gyrus with the superior parietal convolution, and is continued on to the mesial
surface by a narrow annectent which unites it with the posterior part of the marginal
gyrus (paracentral lobule).

OCCIPITAL LOBE. 151

The superior parietal convolution or superior parietal lobule (fig. 101)
is that part of the parietal lobe which lies above the pars honzontalis of the intra-
parietal sulcus, and behind the upper part of the last described convolution, from
which it is imperfectly separated by the upper part of the postcentral sulcus. Its
posterior limit is the boundary of the parietal lobe, viz., the parieto-occipifcal fissure,
round the extremity of which an annectent convolution connects this lobule with
the occipital lobe (upper parieto-occipital annectent gyrus). The superior parietal is
continuous on the mesial surface of the hemisphere with the quadrate lobule. It is
often deeply cut into by an ascending branch of the intraparietal sulcus.

The quadrate lobule (precuneus, fig. 102) is the part of the parietal lobe which
is seen on the mesial surface of the hemisphere. It is bounded in front by the
posterior limb of the paracentral fissure, and behind by the parieto-occipital fissure,
and is incompletely separated from the posterior portion of the limbic lobe by the
postlimbic fissure. Its surface is indented by one or two furrows which cut the
margin of the hemisphere, and extend a variable distance over the surface of the
lobule (precuneate sulci).

The inferior parietal lobule is embraced within the curve of the intraparietal
sulcus. It is bounded behind by the lower limb of the anterior occipital fissure. It
is divided into three gyri, viz. : the supramarginal, the angular, and the postparietal
(fig. 101). The supramarginal convolution lies behind and below the anterior
part of the intraparietal sulcus, beneath the lower end of which it is continuous with
the ascending parietal convolution. It arches round the upturned extremity of the
fissure of Sylvius, to become continuous with the superior temporal convolution
below, and with the angular behind. The angular gyrus, connected in front with
the supramarginal, bends over the end of the parallel (first temporal) sulcus, and is
continued below into the first and second temporal gyri. Behind, it is separated
from the postparietal gyrus by a shallow vertical sulcus, which may be absent. The
postparietal gyrus curves round the upturned end of the second temporal sulcus.
(In the brain figured this appears like a continuation of the first temporal sulcus.)
It is continued below into the second and third temporal gyri.

OCCIPITAIi LOBE. — This lobe is very well marked off in Quadrumana by
the deep cleft (Affenspalte) before mentioned (p. 144) ; but in man the line of
demarcation between it and the adjacent parietal and temporal lobes is less distinct.
It is relatively much larger in Quadrumana, especially in the lower monkeys, than
in man.

The lobe is of pyramidal shape, lying behind the parietal and temporal lobes.
In the adult its length, as compared with that of the whole hemisphere, is about as
21 to 100 (occipital index, Cunningham). It has two free surfaces, an external or
lateral, and a mesial. It occupies the superior fossa of the occipital bone. On the
external surface it is bounded in front by the parieto-occipital fissure, by the anterior
occipital sulcus, and by a line connecting the lower end of this sulcus with the
posterior extremity of the calcarine fissure. The line in question mainly corresponds
with a horizontally-directed sulcus, which is termed by Eberstaller the lateral occipital :
this sulcus may therefore be regarded as the lower boundary of the occipital lobe on
the lateral surface. On the mesial surface of the hemisphere the lobe is marked off
by the parieto-occipital fissure from the quadrate lobule, and by the posterior calcarine
from the temporal lobe (fig. 102).

In assigning the above limits to the occipital lobe I have followed Eberstaller. and have
departed from the usual description which includes in the lobe all the parts behind the plane
of the parieto-occipital fissure, and therefore the posterior parts of the parietal and temporal
lobes as here described. It seems to me, however, that Eberstaller's definition, although it
confines the occipital lobe in man to relatively small limits, has the advantage of assigning
well-marked anatomical boundaries to it and to the adjacent lobes, thus rendering a descrip-
tion of this part of the brain more easy.

152 THE CEREBRAL HEMISPHERES.

EXTERNAL SURFACE. — The bounding sulci of the external surface of the occipital
lobe are, as we have seen, the external part of the parieto-occipital, the anterior
occipital, and the lateral occipital. The parieto-occipital has already been described
(p. 143). The anterior occipital sulcus (transverse occipital of Ecker) is a
transverse furrow, which is laid down as a distinct sulcus in the foetus, but is later
almost invariably joined by the horizontal part of the intraparietal, of which it
then appears to be the bifurcated posterior end (p. 150). In Quadrumana it is
concealed by the occipital operculum, but on drawing this aside it may still be seen
at the bottom of the " Affenspalte." It approaches the mesial border of the hemi-
sphere above, behind the parieto-occipital fissure, from which it is separated by an
annectent gyrus which joins the occipital lobe with the superior parietal lobule.
Its lower end, which is often curved forwards, is usually separated from the lateral
occipital by the inferior parieto-occipital annectent gyrus uniting the occipital
lobe with the postparietal gyrus. In the brain figured (fig. 101), this second
occipito-parietal annectent lies deeply, and the two fissures are superficially
joined.

The lateral occipital sulcus runs somewhat obliquely upwards and back-
wards from a short distance below and in front of the lower end of the anterior
occipital towards the occipital pole of the hemisphere. But before reaching the
pole it generally bifurcates in a Y, one branch curving upwards into the occipital
lobe, the other downwards towards the posterior end of the calcarine ; it may be
embraced by the bifid extremity of the latter. Around its end a lateral occipito-
temporal annectent gyrus curves, uniting the occipital lobe with the third temporal
gyrus. Within the limits of the occipital lobe as here defined there are usually two
or three small sulci of varying extent. These are, however, not constant enough in
position and direction to serve for marking out this surface into distinct gyri.

The external surface lias usually been described (e.g., in previous editions of this work) as
having three gyri, a superior, middle and inferior. But this description does certainly not hold
good for most brains, and if any division is to be made it must be into anterior (between the
anterior occipital sulcus and the upturned end of the lateral occipital) and posterior (behind
the upturned end of the lateral occipital).

MESIAL SURFACE.- — The mesial surface of the occipital lobe is occupied by a
well-marked gyrus termed the cuneate lobule (cuneus) (fig. 102). This is of u
triangular shape, and is bounded in front by the parieto-occipital fissure, and below
by the calcarine, while above and behind it reaches the margin of the hemisphere
and is continuous with the external surface. It is indented by two or three shallow
vertical sulci.

The parieto-occipital and calcarine fissures which bound the mesial surface have
already been described, as well as the deep annectent gyri which pass across them
and connect the cuneus with the adjacent lobes (see p. 144).

The superior longitudinal venous sinus in passing downwards causes an impression on the
inner side of the occipital pole of the hemisphere (Bastian). This impression is generally
found on the right side, but sometimes on the left.

According to the usual description, which has been followed in previous editions of this
work, the occipital lobe has a tentorial surface, comprising the lingual gyrus and posterior
part of the occipito-temporal gyrus (fusiform lobule), which run in a sagittal direction, and
are separated from one another by the posterior end of the collateral fissure. But by confining
the occipital lobe to the limits above assigned, these gyri and sulci become entirely included
in the temporal lobe, along with which they will accordingly be described.

TEMPORAL LOBE. — The temporal or temporo-sphenoidal lobe is bounded
above for two-thirds of its length at first by the stem and afterwards by the
posterior limb of the fissure of Sylvius, which separates it from the frontal and part

TEMPORAL LOBE. 153

of the parietal. Behind and above it is continuous with part of the parietal lobe.
Behind, it is separated from the occipital lobe by the lateral occipital sulcus. It is
somewhat pyramidal in shape, having three surfaces, viz., lateral, superior and
inferior, the superior concealed within the fissure of Sylvius. The under surface
adjoins the limbic lobe, being separated from the hippocampal gyrus of that lobe by
the collateral fissure. The rounded apex of the pyramid is free, is directed forwards,
and lies underneath the orbital surface of the frontal lobe, from which it is separated
by the broad commencement of the Sylvian fissure.

GYRI AND SULCI OF THE UPPER SURFACE. — The upper surface of this lobe,
directed towards the insula and fronto-parietal operculum, is marked by two or three
transverse temporal gyri (Heschl). On the nearly smooth part of the surface in
front of these are three short gyri (m, fig. 108) separated by shallow sulci, which are
directed from the gyrus longus insulas towards the tip of the temporal lobe.

SULCI AND GYRI OF THE LATERAL AND UNDER SURFACES. — On these surfaces
there are four sulci with an antero-posterior direction. The first or superior
temporal sulcus, also termed from its relation to the Sylvian fissure the parallel-
fissure (fig. 101, /j), is an important furrow, appearing in the sixth month, and being
constant in the Primates. In many monkeys it is more extensive than in man.
nearly reaching the parieto-occipital fissure at the margin of the hemisphere. The
angular gyrus curves round its extremity. Both this and the second temporal turn
upwards as they poss back. The upturned extremity of the second sulcus may
appear as a continuation of the parallel, as in the brain here figured (fig. 101). The
fissure is sometimes interrupted by a small gyrus connecting the convolutions above
and below it. The second temporal sulcus (£>) runs parallel to and below the
last, but is less constant in extent and direction. It is often interrupted by one or
more vertical connecting gyri. The postparietal gyrus curves round its extremity.
The third temporal sulcus ( /;j) is seen on the under surface of the lobe, extending
behind nearly to the occipital pole. It is often interrupted near its anterior and
posterior ends, and sometimes also about the middle by annectent gyri. In front it
generally fails to reach the extremity of the lobe, which forms a smooth " pole " from
which most of the sulci diverge. A fourth temporal sulcus (£4) is formed by
the collateral fissure, which has already been noticed (p. 145) (figs. 101, 103).

On the lateral surface of the lobe three convolutions can usually be distinguished.
The first or superior temporal gyrus (fig. 101, F-^ bounds the posterior limb of
the Sylvian fissure below, and is continuous behind with the supramarginal and to a
less extent with the angular convolution of the parietal lobe. The second temporal
gyrus (T^) is continuous with the angular and postparietal gyri. The third
temporal gyrus (T3) is continuous with the occipital lobe by the annectent gyrus
which passes between the calcarine and lateral occipital sulci. On the under surface
of the lobe is the fourth temporal gyrus, lying between the third temporal
sulcus and the collateral fissure. The second and third gyri are convolutions of
some thickness, and are a good deal interrupted by transverse and oblique secondary
sulci. The fourth, which was formerly known as the first occipi to-temporal, is
narrower, and more sharply marked off by its bounding sulci. Its posterior part,
which has been termed the fusiform lobule, is usually described as belonging to the
occipital lobe (see previous page). Lastly, between the posterior part of the collateral
and the calcarine fissure is a fifth temporal gyrus, which was termed by Huschke
the lingual lobule, but it is better termed infracalcarim gyrus (subcalcarine gyrus of
Wilder). This is continuous in front with the hippocampal gyrus of the limbic
lobe (see below). It is joined by two deep annectent gyri, which pass across the
posterior calcarine fissure, connecting this gyrus with the cuneus (fig. 102, 2 and 3).

The temporal lobe lies in the middle fossa of the skull, and its posterior part
overlies the tentoriuui.

154

THE CEREBRAL HEMISPHERES.

THE CEKTTRAIi LOBE OR ISLAND OF REIL. — This lobe is entirely
concealed in the adult human brain within the fissure of Sylvius, the margins of
which form opercula (see p. 142) which overlap the lobe. The central lobe corre-
sponds with the corpus striatum on the interior of the hemisphere (fig. 88), and
probably in consequence of its close connection with this mass of grey matter, which
appears early as a thickening of the lateral wall of the vesicle of the cerebral hemi-
sphere (vide Embryology, Vol. I., p. 69), this particular part of the hemisphere does
not keep pace with the general expansion which the hemisphere-vesicles undergo,
and hence in consequence of that expansion it becomes overlapped and concealed by
the rest of the hemisphere. On account of this early fixation and the close topo-
graphical relation between it and the largest of the basal ganglia, the central lobe
(along with the basal ganglia and the continuation of the peduncles between them)
is frequent!/ spoken of as the stem (German, Slammtheil) of the hemisphere, the
remainder of the cerebrum, which covers it in, being known collectively as the mantle.

To see the island it is necessary to cut away the opercula (fig. 108). It then
appears as a triangular surface somewhat bulged outwards, the base of the triangle

Fig. 108. — ISLAND OF REIL EX-
POSED BY CUTTING AWAY THK

UPPER OPERCULUM AND DRAW-
ING ASUNDER THE ORBITAL
AND TEMPORAL OPERCULA.

(Eberstaller. )

s.c., sulcus centralis insulse ;
1, 2, 3, gyri breves ; 4, 5, gyms
longus ; s.li.a., s.H.ft., s.K.p.,
anterior, superior, and posterior
limiting sulci ; I, limen insulse ;
F, orbital part of third frontal
gyrus; 2\, Tz, first and second
temporal gyri; x.y, upper trans-
verse temporal gyri ; g. tr. i. , gyrus
transversus insulse, passing at a,
into the orbital part of the third
frontal ; b, connection of gyrus
longus insulse with apex of tem-
poral lobe ; m, short gyri on the
upper surface of the temporal pole.

being directed upwards and the apex being at the vallecula Sylvii. This surface is
marked out by shallow sulci, which have a fan-like arrangement converging from the
base towards the apex of the triangle, into several straight gyri having a similar con-
vergent course. One of these sulci, which is deeper and appears earlier than the rest,
and is also more constant in lower Primates, has been termed the sulcus centralis
insulse (Guldberg) (fig. 108, s.c.), and this serves to subdivide the lobe into two
parts, aprecentral and postcentral lobule. Since the line of.direction of this sulcus
nearly corresponds with that of the fissure of Rolando in the mantle, the pre- and
post-central parts of the island similarly correspond to the frontal and parieto-
temporal lobes of the mantle ; and they are in fact in continuity with the parts
of those lobes which form the opercula. The island is, however, separated from
these adjacent parts by a sulcus (sulcus limitans insulse) which almost entirely
surrounds it. and which is itself formed of an anterior, a superior, and a posterior
part (fig. 108). The anterior and posterior parts of the limiting sulcus are,
however, deficient near the apex of the lobe, so that there here occurs a direct
continuity (by a small convolution, the gyrus transversus insulce of Eberstaller)
between the orbital part of the third frontal convolution as it dips round the margin
of the Sylvian fossa, and the precentral lobule on the one hand, and between the
linibic lobe and the extremity of the postcentral lobule on the other hand.

LIMBIC LOBE. 155

The precentral lobule of the insula is formed of a few short convolutions (gyri breves)
(fig. 108, 1, 2, 3) converging from the base of the triangle but falling short of the apex of the lobule,
which is smooth and forms a slight prominence (pole of the island, p). These convergent gyri
are usually three in number (anterior, middle, and posterior), being subdivided in this manner
by secondary and somewhat shallow sulci, having the same direction. The most marked of
these sulci lies between the middle and posterior gyri breves, and has been named sulcus pre-
centralis insula;. A fourth small gyrus is described by Eberstaller as lying deeply underneath
the orbital operculum. This he has termed the gyrus brevis accessorius. This accessory gyrus,
and usually also the anterior of the three gyri breves, look forwards, lying upon an anterior
surface of the insula, which is sometimes nearly at a right angle with the lateral or general
surface, in other brains hardly marked off from it. Its grey matter is continued over the
anterior limiting sulcus into that of the orbital gyrus. The grey matter of the rest of the
precentral lobule is continuous superiorly with that of the frontal lobe, inferiorly with that
of the anterior perforated space. The inferior transitional part has been termed the threshold
of the island (limen insula!, Schwalbe).

The postcentral lobule (gyrus longus insula- of Giacomini (fig. 108, 4, 5) ) is also often
subdivided at its upper end by a longitudinal furrow (sulcus postcentralis insulce*) into two parts,
anterior and posterior. Its grey matter is continuous below with the tip of the hippocampal
gyrus, laterally with that of the first temporal gyrus, above and posteriorly over the limiting
sulci with the grey matter of the parietal and temporal opercula.

The three principal furrows of the insula (sulcus centralis, s. precentralis, and s. post-
centralis insular), which radiate from the vallecula Sylvii, have been compared with the three
similarly radiating fissures of the mantle, viz., the fissure of Rolando, the precentral fissure,
and the intraparietal fissure. They are not, however, directly continuous with those, being
arrested at the sulcus limitans insulte. Sometimes the fissure of Rolando is continued by a
small sulcus (transverse precentral) almost into the s. centralis insulse. Below and anteriorly
the sulcus centralis insulas comes into close relationship with the extremity of the calloso-
marginal sulcus.

LIMBIC LOBE. — The callosal gyrus, with its continuation the hippocampal
gyrus, were separated by Broca, on morphological grounds, from the other parts
of the hemisphere, as a distinct lobe, intimately united in front and below
with the olfactory lobe ; and the name of grande lobe limbique was given by
him to these combined lobes. To this lobe of Broca, Schwalbe added the other
central parts of the mesial wall of the hemisphere, viz., the lamina septi lucidi and
the dentate convolution, as well as the fornix ; looking upon these as representing
an inner encircling convolution concentric with the gyrus fornicatus and uncinatus,
and naming the whole lobe thus reconstituted, the " falciform lobe," the olfactory
lobe being, however, excluded.

To the parts included by Schwalbe there must now be added a rudimentary
supracallosal gyrus (represented in man principally by the longitudinal strise of
the corpus callosum), which is continuous with the dentate convolution posteriorly,
and with the rudimentary gyrus geniculi (see p. 1 58) anteriorly. The lobe must
further include the peduncles of the corpus callosum (see p. 127), which appear to
represent a rudimentary gyrus (gyrus subcallosus, Zuckerkandl), and also another
rudimentary gyrus underneath the corpus callosum, partly imbedded in and
intimately connected with the fornix, to which the name of gyrus infracallosus or
gyrus for nicis may be applied.

As thus constituted the limbic lobe is bounded circumferentially mainly by two
important fissures, the calloso-marginal above, and the anterior part of the collateral
below, while the less constant postlimbic sulcus separates it behind from the
parietal lobule, and the anterior end of the calcarine cuts into it just below the
splenium.

The circumferential boundary is least distinct opposite the quadrate lobule, from which it
is only separated by the small postlimbic sulcus, which in man is only occasionally continued
into the calloso-marginal. But in many animals the fissure which forms the external boundary
is uninterrupted or nearly so, and forms the limbic fissure of Broca. This might perhaps
more appropriately be termed the outer limbic fissure, since the callosal sulcus and the
hippocampal fissure form together a second crescentic fissure within the limbic lobe, which
may be distinguished as the inner limbic fissure. The internal limit of the lobe is formed by
the Jissura choroidea (Schwalbe), through which the choroid plexus is invaginated into the

156 THE CEREBRAL HEMISPHERES.

lateral ventricle. The lobe is pierced by the great commissure of the hemispheres (the corpus
callosum) and also by the anterior commissure. It is connected by annectent gyri with the
lingual gyrus of the temporal lobe (see p. 153), with the cuneus of the occipital lobe (by a

Fig. 109. — DIAGRAM OF THE LIMBIC LOBE.

gyrus hidden within the internal parieto-occipital fissure), with the quadrate lobule, with the
orbital part of the frontal lobe, with the anterior part of the temporal lobe, and with the post-
central lobule of the insula.

Each end of this crescentic lobe is connected with one of the roots of the olfactory tract,
viz., the commencement of the gyrus fornicatus with the mesial root and the termination of
the hippocampal gyrus with the lateral root.

CONVOLUTIONS AND FISSURES IN THE LIMBIC LOBE (fig. 102). — Gyrns forni-
catus, gyrus cinguli, callosal gyrus. This is an extensive convolution which
lies between the marginal gyrus of the frontal lobe and the quadrate lobule of the
parietal lobe above and the corpus callosum below. The convolution sweeps round
the corpus callosum, beginning below its rostrum, where it abuts on the subcallosal
gyrus, and ending a little below the level of the splenium by becoming continuous
with the posterior end of the hippocampal gyrus. Where it passes into that gyrus
it is much narrowed (isthmus).1 It is separated from the corpus callosum by a fissure
which is termed the callosal sulcus.

The hippocampal gyrus (subiculwn cornu ammonis), also known, together
with the infracalcarine, as the uncinate gyrus, is continued from the isthmus of
the callosal convolution, and passes forwards above the anterior part of the collateral
fissure towards the apex of the temporal lobe (figs. 102, 103). It ends before
reaching this, however, becoming considerably thickened, and forming a recurved
projection which looks backwards and inwards, and is known as the uncus. The
hippocampal gyrus is covered superficially by a well-marked reticular layer of white
fibres (s'ubstantia reticularis alba, Arnold (fig. 103, s.r.a.) ).

The dentate gyrus (fascia dentata Tarini(fi.g. 102, fig. 110, f.d.) ) lies above the
hippocampal gyrus, from which it is separated by the hippocampal or denlatefissure (f.ti).

1 By some authors the term gyrus fornicatus is made to include the hippocampal gyms.

THE DENTATE GYRUS.

157

It is a narrow convolution having a peculiarly toothed or notched appearance at its free
border, hence the name dentate. Above and overlapping it is the fimbria, from which
it is separated superficially by a shallow sulcus (fimbrio-dentate,f.f,-d.\ narrow in front

. ,'>.:• .*^

Fig. 110. — DIAGRAM OF A SECTION THROUGH THE LEFT HIPPOCAMPAL REGION (E. A. S.)

b.e., basis cerebri ; tr., tractus options ; n. o., nucleus caudatus ; /. rJi., fissura choroidea ; f.,
firnbria ; f.f.-d., fissura fimbrio-dentata ; /. d., fascia dentata, /. Ji., fissura hippocampi ; //, hippo-
campus major; a., alveus ; e. coll., eminentia collateralis ; c. 1., cornu inferius ventriculi ; //, gyrus
hippocampi ; m., its medullary centre ; s.r.a., substantia reticularis alba ; /. coll., fissura collateralis.

but broadening out behind, where it forms
a triangular depression below the splenium
of the callosum. The gyrus dentatus begins
posteriorly just behind and above the
splenium by a fine curved lamina (fasciola
cinerea), which is continuous with the
longitudinal striae (both lateral and mesial)
of the corpus oallosum (p. 127). From
here it bends downwards, lying along the
isthmus of the gyrus fornicatus and then
along the upper border of the hippocampal
gyrus ; .here the posterior pillar of the
fornix passes to its upper border in continuity with the fimbria (see p. 130). An-
teriorly it is continued into the cleft between the hippocampal gyrus and its uncus,
where it becomes lost to view. But if this cleft be opened out (fig. Ill) the dentate
gyrus is seen to exhibit a sharp curve within it, and in continuity with the curved
end a greyish band emerges from the cleft and passes transversely over the uncus
to disappear on the ventricular surface of that gyrus (Luschka, Giacomini).

The part of the gyrus dentatus which lies below the splenium is sometimes much more
developed than usual, and shows strongly marked folds or dentations which recall the broad

Fig. 111. — HIPPOCAMPAL GYRUS AND FASCIA

DENTATA, SHOWING THE CONTINUITY OF THE
LATTER WITH THE BAND OF GlACOMINI
PASSING OVER THE UNCUS. (Testllt.)

158 THE CEREBRAL HEMISPHERES.

and secondarily convoluted gyrus dentatus which covers the under surface of the splenium in
some mammals (G. Retzius).

Hidden beneath the posterior part of the callosal gyrus. between this and the subsplenial
part of the gyrus dentatus, a small projection of the cortex is usually to be found, about 1 cm.
long and 2 mm. to 4 mm. broad, marked by 1 to 4 semicircular eminences. This has been described
(by A. Retzius originally, and more recently and fully by Zuckerkandl) under the somewhat
misleading name of callosal r/yrus (Balkenwindung), but is not to be confounded with the
gyrus cinguli which has long been so denominated. It is best developed in osmatic mammals.

The fimbria (fig. 102, y?) represents the white matter of the hemisphere, which
here comes to the surface along the side of the dentate gyrus. It is continuous
with the alveus which covers the hippocampus major within the lateral ventricle,
and this is continuous with and forms part of the central white matter. The
fimbria itself, however, appears to be actually formed of fibres which are prolonged
into it posteriorly from the pillars of the fornix : anteriorly it is continued into the
white matter of the uncus. In section the fimbria appears as a somewhat club-
shaped expansion of the alveus, exhibiting a hook-like mesial prolongation (fig. 1 10,/).
This is the section of a thin lamina (tcenia fimbrife), continuous with the epithelium
covering the choroid plexuses which here invaginate the ventricular epithelium.

The only sulcus within the limbic lobe which remains to be described (the
callosal sulcus and the fimbrio-deniate sulr-us having been already noticed) is the
hippocampal or dentate fissure (fig. 102, h}. This begins as a shallow furrow
just above the posterior end of the splenium corporis callosi, between the fasciola
cinerea and the end of the gyrus fornicatus, it then lies between the remainder of
the dentate gyrus above and the isthmus gyri fornicati and hippocampal gyrus below,
and becoming deeper as it passes forwards ends in the bend between the hippocampal
gyrus and its uncus. This fissure causes the elevation of the hippocampus major
or cornu Ammonis in the descending horn of the lateral ventricle (fig. 110).

Gyrus fornicis. — The fornix which has already been in the main described (p. 129) also
belongs to the limbic lobe as here defined. It contains an association-bundle uniting the
hippocampus major with the olfactory lobe. This bundle, the olfactory bundle of the cornu
Ammonis (Zuckerkandl), best developed in osmatic mammals, is contained within the body of
the fornix, but leaves the anterior pillar to pass in front of the anterior commissure and then
to run in the subcallosal gyrus to the vallecula Sylvii. Here it divides into two parts, one
(pars olfactoria) passing by the anterior circumference of the lamina perforata anterior to the
inner root of the olfactory tract, and the other (pars temporalis) at the hinder border of the
anterior perforated lamina to the point of the hippocampal gyrus. This is the band which has
been described (by F. Arnold and Broca) as continuing the peduncle of the corpus callosum
with the hippocampal gyrus.

In the monkey there is a band of grey matter running along the upper surface of the
fornix, on each side near the middle line, wedged in between it and the corpus callosum.
This closely resembles the supracallosal gyrus above the callosum (see below), and appears to
be part of another rudimentary gyrus which may be termed gyrus infracallosus, or, including
certain patches of grey matter which occur here and there in the substance of the fornix,
gyrus fornicis.

The cingrulum, which also belongs to the limbic lobe, is a tract of association-fibres run-
ning in the gyrus hippocampus and gyrus fornicatus. The bundle has for the most part a
longitudinal course within the white matter of these gyri ; but the fibres probably commence
in the cortex, and since they constantly tend, as the whole bundle courses longitudinally, to
diverge into the adjacent white matter of the hemisphere, it appears probable that they
connect the hippocampal and callosal gyri with the cortex of the outer surface of the hemi-
sphere (Beevor). A bundle of fibres having a somewhat similar course in the anterior
descending part of the gyrus fornicatus is usually described as part of this tract ; but according
to Beevor it is doubtful if these fibres can be considered to belong to the cingulum ; at all
events, their continuity with the remainder of that tract could not be traced.

Gyrus limbicus. — The longitudinal striae of the corpus callosum (p. 127) belong to a thin
lamina of grey matter which extends over the surface of the corpus callosum from the lower
edge of the gyrus fornicatus, and is much better developed in osmatic mammals than in Primates
(Valentin, Jastrowitz). The striag, together with this grey matter, represent a degenerated con-
volution (supracallosal gyrus, Zuckerkandl), which is continuous posteriorly with the fasciola
cinerea, i.e., with the dentate gyrus. Together with another degenerated gyrus in front, which is
represented only by the prolongation of the stria medialis (gyrus geniculi of Zuckerkandl) these

THE OLFACTORY LOBE. 159

form a rudimentary gyrus (bordering gyrus, gyrvs marglnalis* Germ. Randwindung), which is
curved around the brain-stem and the central parts of the hemisphere, lying within and concen-
tric with the larger and well-developed gyrus formed by the fornicate and hippocampal gyri.
The lamina of the septum lucidum, and the so-called peduncle of the corpus callosum (gyrus
subcallosus of Zuckerkandl) also belong to this bordering gyrus, but have become separated
from the supracallosal part by the development of the corpus callosum ; and the gyrus
inf racallosus (where this exists) and the fornix and fimbria may also be considered to form
part of it.2

OLFACTORY LOBE. — This lobe (fig. 112) lies at the ventral aspect of the
frontal lobe. It is rudimentary in man and other Primates, and in the seals, and is
lacking in Cetacea, but in all other mammals (osmatic mammals, Broca), and in
vertebrates generally, it is well developed and forms a distinct portion of the cerebral
hemisphere, enclosing an extension of the ventricular cavity. In some mammals
(e.g., horse) this extension remains throughout life in free communication with the
anterior horn of the lateral ventricle, in others (e.g., dog) the communication is lost.
In the human foetus of from two to four months, it appears as a hollow projection
of the fore-brain, but as the Avails of this projection thicken by the development
of nervous tissue within them, the cavity becomes gradually obliterated, and is
ultimately entirely occupied by a mass of neuroglia (central neuroglia of the olfactory
tract and bulb). Compare Vol. I., pp. 71 and 79.

Anteriorly the olfactory lobe is connected with the olfactory cells of the olfactory
mucous membrane, posteriorly it is connected with the two extremities of the limbic
lobe.

The olfactory lobe may be described (His) as composed of two parts or lobules,
an anterior and a posterior. The anterior olfactory lobule comprises (1) the olfactory
bulb, which rests on the cribriform plate of the ethmoid bone, and receives the fibres
of the olfactory nerves, which originate in the cells of the olfactory mucous
membrane, (2) the olfactory tract, which lies in the olfactory sulcus of the frontal
lobe, and posteriorly bifurcates into two roots, mesial and lateral, which diverge
as they pass backwards and enclose (3) a space, the trigonum olfaclorium, which is
also known as the middle or grey root of the tract, (4) the area of Broca (His), a
portion of grey matter lying between the mesial root and the peduncle of the
corpus callosum, and continuous with the commencement of the callosal gyrus.
This area is separated from the posterior part of the gyrus rectus of the frontal lobe
by an oblique sulcus (fissura serotina, His).

The posterior olfactory lobule is marked off from the anterior by a curved fissure
(fissura prima, His). It is formed by the portion of brain cortex, which
appears on the surface at the anterior perforated space, and is bounded mesially
by the peduncle of the callosum (gyrus subcallosus of Zuckerkandl), anteriorly by the
fissure just referred to, whilst laterally it is continued into the vallecula Sylvii,
and is concealed by the temporal lobe which overlaps it. The continuation of the
lateral root of the olfactory tract courses lateral wards and backwards over the surface,
as it passes towards the anterior end of the hippocampal gyrus.

The olfactory bulb (figs. 103, 112) is oval in shape and of a reddish-grey
colour when viewed from the ventral aspect. It is nearly a centimeter long and
about a third of this in width ; from its posterior extremity the olfactory tract
emerges. Its dorsal surface, which is in contact with the frontal lobe, is white and
is directly prolonged into the tract. This surface presents a longitudinal ridge
which fits into the anterior end of the sulcus olfactorius of the frontal lobe.

The olfactory tract, sometimes erroneously spoken of as the olfactory nerve, is
a band of white matter, flattened on the ventral aspect but ridged along the dorsal

1 Not to be confounded with the gyrus marglnalis on the mesial surface of the frontal lobe (see p. 148).

z Zuckerkandl describes two bordering gyri, an outer and inner, the outer being formed by the dentate
gyrus, the gyrus supracallosus and the gyrus geniculi, and continued into the inner root of the olfactory
tract ; the inner by the fimbria, fornix, lamina septi lucidi. and gyrus subcallosus.

160

THE CEREBRAL HEMISPHERES.

aspect (where it fits into the olfactory sulcus), and therefore triangular in section.
It measures about 2 centimeters in length and 2| millimeters in breadth, being
narrowest anteriorly where it passes out of the bulb, and broadening posteriorly as it
bifurcates to form the roots. As already stated it encloses a central grey substance
formed of neuroglia.

The trigomim olfactoriiim and the area of Broca are in fact parts of one
and the same area of grey matter which forms the base of the anterior olfactory
lobule, and is traversed by the roots of the olfactory tract. This area is separated
from the peduncle of the callosum and the posterior olfactory lobule by the fissura
prima, and the mesial root of the olfactory tract in passing over its ventral surface
subdivides it superficially into its two parts. Of these the area of Broca receives
many fibres from the mesial root as this passes over the surface, whilst the trigonum
olfactorium receives others which are directly prolonged into it from the posterior

Fig. 112. — OLFACTORY LOBE OF THE
HUMAN BRAIN (His).

Bu, olfactory bulb ; T, tract; Tr.o.,
trigone ; R, rostrum of corpus callosum ;
p, peduncle *of corpus callosum, passing
into, g.s, gyms subcallosus (diagonal
tract, Broca) ; Br, Broca's area ; F.p,
lissura prima ; F.s, fissura serotina ; C.a,
position of anterior commissure ; L.t,
lamina terminalis ; Ch, optic chiasma :
T.o, optic tract ; p.olf, posterior olfactory
lobule (or anterior perforated space) :
m.r, mesial root ; I. r, lateral root of
tract.

end of the tract, and which some-
times form a distinct middle root
of the tract. The ultimate des-
tination of these fibres which pass
into the trigone is not accurately
known, but some appear to join
the anterior commissure and to
be conducted by this into the
posterior part of the temporal

lobe, and others, according to Meynert, may pass across in this commissure to the
temporal lobe and hippocampal region of the opposite side, an " olfactory chiasma "
being thereby produced. The evidence in favour of this crossed connexion is,
however, at present insufficient. Fibres from the posterior end of the olfactory
tract also pass directly into the white matter of the frontal lobe : these have been
named the upper or dorsal root of the olfactory tract (Henle).

The outer or lateral root passes as already stated over the outer part of the
substantia perforata anterior, and becomes lost to view in the depth of the vallecula
Sylvii. In osmatic mammals it can be traced without difficulty into connection
with the anterior part of the hippocampal gyrus, and, according to Luys, with
the nucleus amygdalae. The inner or mesial root is recurved sharply around the
posterior limit of Broca's area, and its fibres pass partly into this, partly into the
callosal gyrus. The olfactory tract has thus a relation to the limbic lobe which has
been compared to that of the handle of a tennis-racquet to the ring of the blade, the
two extremities of the curved limbic lobe being continuous respectively with the inner
and outer roots of the olfactory tract (fig. 109). The combined olfactory and limbic
lobes may be spoken of collectively as the rhinencephalon ; it is marked off from the
rest of the hemisphere by the combined calloso-marginal, postlimbic and collateral
fissures forming together the limbic fissure, and in its development it varies directly
with that of the olfactory organ. This co-relation in development applies more

p.olf.

T.o.

VARATIONS IN FISSURES AND CONVOLUTIONS OF BRAIN. i6l

especially to the hippocampal convolution, which in many smooth-brained osmatic
mammals forms a considerable proportion of the hemisphere (lobus hippocampi).

The term rhinencephalon is limited by Turner to the olfactory and hippocampal lobes, but
there seems no sufficient reason for excluding the remainder of the limbic lobe, the several parts
of which are all closely inter-related. At the same time it must be pointed out that the
limbic lobe unquestionably subserves other functions beside that of a central organ for the
olfactory sense, since it is present even in those mammals (Delphinidse) which are devoid of
an olfactory sense, and in which the olfactory lobe proper is entirely absent. The results of
experiment seem to indicate an association of parts of the limbic lobe with the perception of
tactile sensations. (Consult on the comparative development of the rhinencephalon and the
mantle in mammals, " The Convolutions of the Brain, a Study in Comparative Anatomy,"
by Professor Sir W. Turner, Journal of Anatomy, October, 1890.)

ON THE VARIATIONS WHICH OCCUR IN THE DISPOSITION OP THE FISSURES AND
CONVOLUTIONS IN INDIVIDUALS OF DIFFERENT AGE, SEX, INTELLECTUAL
DEVELOPMENT, AND RACE.

Very considerable variations are found in the course and relative development of the
fissures and convolutions, "and this not only in different individuals, but also on opposite sides
of the same brain. Even the principal fissures, under which term may be included both those
which occur as complete folds of the hemisphere-wall (Sylvian, hippocampal, calcarine,
parie to-occipital, and collateral), and those which are the first to make their appearance (about
the sixth month of fcetal life) as indentations of the smooth surface of the mantle (precentral,
Rolandic, intraparietal, parallel, olfactory, calloso-marginal), are very subject to modifi-
cation, as may partially be inferred from the detailed accounts which have already been
given. Although a considerable amount of attention has been paid by several observers
to these variations, and of late years especially by Pansch, Sernoff, Huschke. Riidinger,
Giacomini, Eberstaller, and Cunningham, it cannot be considered as proved that there is any
constant relationship between any of the variations which are found to occur, and either the
age, sex, occupation, or even the race of the individual. Various attempts have from time to
time been made to determine in particular a sexual distinction, but it has invariably appeared
that the inferences which had been drawn from an insufficient number of observations are not
borne out by a more extended series. It is more probable that certain racial differences may
ultimately be established when a sufficient number of brains belonging to individuals of
other than European races shall been carefully examined, but up to the present the materials
for such comparison have not been abundant enough. In brains of individuals belonging to
lower races which have been described (Bushmen, Fuegians, Lapps, and others), it has not
appeared that there is any distinct lack of complexity in the convolutions as compared with
ordinary European brains, but it is probable that if a large number were to be examined the
average complexity in such races would be below that of the average European brain. This
is in fact stated by Parker to be the case for the brain of the negro, but the number examined
were not sufficient to be considered conclusive. There is apparently, however, more distinct
evidence to show that complexity of convolution generally goes hand in hand with intellectual
development of the individual, for in many cases in which the brains of men of known
intellectual capacity have been examined, the complexity, due partly to the greater develop-
ment of secondary and tertiary sulci, partly tc the more curved course taken by the
principal sulci, has been decidedly, in some instances extraordinarily, marked. Indeed,
in some cases a relationship seems to have been apparent between a particular type
of mental development and a special part of the brain ; thus it was found that the brain
of the great French orator, Gambetta, showed an especial degree of complexity of the third
left frontal convolution. In skilled artisans it might be expected that the part of the brain
which is connected with the voluntary movements of the hands and fingers might be found
to be especially developed, and in one or two individual cases this has been noticed, but the
material for a general statement regarding such relationship is insufficient. Benedikt, from
the examination of the brains of a large number of individuals belonging to the criminal class,
was of opinion that there exists amongst these an undue tendency to the formation of four
antero-posterior convolutions in the frontal lobe, or in other words, an undue tendency to the
appearance of the paramesial and middle frontal sulci. Although apparently supported by a
few observations by other anatomists, this supposition has not borne the test of more extended
observation ; and, indeed, the so-called " criminal " type was actually less frequent in the
brains of convicts examined by Giacomini than in those of ordinary persons.

162 THE CEREBRAL HEMISPHERES.

ON THE CAUSATION OF THE GYRI AND SULCI OF THE BRAIN.

Various explanations have been offered to account for the convoluted form of the cortex.
These are based partly on mechanical considerations, e.g., the resistance offered by the larger
blood-vessels and undue growth of the brain as compared with that of its enclosing skull-
capsule, partly on physiological or physiologico-mechanical considerations, which suppose
that there is a relative increase of functional activity of certain parts as compared with others,
resulting in an increased growth of those parts, and hence their projection in the form of gyri.
These theories, however, are quite insufficient to account for the convoluted formation, since
it can be shown (1) that the blood-vessels for the most part do not correspond with the fissures,
nor do they lie in the depth of the fissures, when they happen to coincide with them ; (2)
that the brain does not fill the skull at the time the permanent fissures make their appearance ;
(3) that in the animal series there is no direct relationship between intellectual development
and cerebral convolution. Further, it may be stated that no theory which will not also
account for the fissures and lamina? of the cerebellum as well as the convolutions of the
cerebrum can be regarded as satisfactory.

It has. however, lately been pointed out by Jelgersma that a simple mathematical
explanation exists for the existence of a convoluted surface. The one feature which mammals
with smooth brains have in common is smallness of body ; whereas those mammals which
possess convoluted brains are invariably found to be of relatively large size (Dareste). In
other words, small mammals have smooth brains, however high they may be on the animal
ladder, and in spite of their possessing a high degree of intelligence (e.g., certain monkeys),
whilst large mammals have convoluted brains, although their intellectual development may
be relatively low (e./;., cetaceans). " The grey cortex of the brain, which in members of the
same species maintains a tolerably constant thickness, increases by surface extension.
Further, with every advance in the growth of the grey matter, there must be a proportionate
increase of the subjacent white matter. The geometrical law involved is simply this — that
in the growth of a body the surface increases with the second, but the interior with the third
power of the radius. From this it is evident, seeing that the proportion of internal white
matter and external grey matter is in all cases a uniform one. that in the evolution of a large
animal out of a small animal a disproportion between the grey capsule and the white core of
the cerebrum must result. This is compensated for by the extended cortex placing itself in
folds or puckers. Jelgersma further points out that the extent of the cerebral surface
depends upon two factors, namely, (1) the absolute quantity of the grey matter, and (2) the
thickness with which this is spread over the surface. The absolute quantity of grey matter
present is determined by the bulk, or by the psychical endowments of the animal, or by both
of these factors together. On the other hand, although the thickness of the grey cortex is
very much the same in the same species, it differs considerably in different animal groups ;
and it follows from the theory which he has advanced that the more sparsely the grey
substance is spread over the surface of the white matter, the richer will be the convolution
type. In the cetacean cerebrum the grey cortex is exceedingly thin, and it is due to this that
the surface shows such an extreme condition of complexity." '

Cases in which there is a congenital absence of the corpus callosum are characterized by a
peculiar type of convoluted surface, the fissures and convolutions showing a strong tendency
to radiate from the Sylvian fossa. This is partly due, according to Cunningham, to a retention
of certain of the primitive fissures which appear about the third or fourth month, are due to
unfoldings of the whole thickness of the cerebral wall, and are mostly quite transitory ; but
they cannot all be thus accounted for. There is often in these cases an intricacy of pattern
displayed which is comparable to that of the cetacean hemisphere, and may be very possibly
produced in a similar manner.

The same law by which the formation of the cerebral convolutions is accounted for,
likewise explains the development of the cerebellar folia, and of the wavy outline of the
corpora dentata of the cerebellum and olives.

Jelgersma's theory is not complete in so far that it does not explain why the convolutions
should tend to assume certain patterns in certain groups. It is not improbable that these
differences may be determined by variations in the relative functional importance of
different parts, producing a corresponding variation in the extent of grey matter which has
to be provided for, and relative increase of this can only be obtained by local puckering
(Cunningham). There is no doubt, however, that the formation of the various cerebral
patterns, fairly constant for the same species, is scarcely susceptible of any very simple
explanation, and that for the present we must rest satisfied with the statement of the fact.

1 D. J. Cunningham, Address delivered at the opening of the section of Anatomy and Physiology at
the annual meeting of the British Medical Association, 1890.

PROJECTION FIBRES. 163

INTIMATE STRUCTURE OF THE CEREBRAL HEMISPHERES.

STRUCTURE OF THE WHITE MATTER.

The cerebral hemispheres, like the rest of the encephalon, are composed of white
and grey substance, the white pervading nearly the whole of the middle of each
hemisphere, where it forms what is known as the medullary centre, and extending
into the convolutions ; the grey forming a covering of some thickness over the
whole surface of the convolutions (cortex), and occurring also at the base of the
hemisphere in the form of the so-called basal ganglion (corpus striatum).

The white matter consists of medullated fibres, varying in size in different parts,
but in general smaller than those of the cord and bulb. They are arranged in
flattened bundles separated by neuroglia ; the bundles have a somewhat rod-like
appearance in transverse section.

The fibres of the medullary centre, though forming many different groups, may
be referred to three principal systems, according to the general course which they
take, viz. : — 1. Projection-fibres, which pass from the isthmus encephali to the
hemispheres, or vice versa. These fibres increase in number in passing the optic
thalami and corpora striata, beyond which they spread in all directions into the
hemispheres. 2. Transverse or commissural fibres, which connect the two hemi-
spheres together. 3. Association-fibres (Meynert), which, keeping on the same side
of the middle line, connect near or distant parts of the same hemisphere.

1. The projection fibres in each hemisphere are continuous in part with the
fibres of the crusfca, in part with those of the tegmentum, the latter probably
indirectly through the corpus striatum and optic thalamus. They are in great
measure, if not wholly, direct prolongations of the axis-cylinder processes of cells of
the cortex (see diagram, fig. 20, p. 23).

a. The fibres which are continuous with those of the crusta pass in the internal
capsule, between the optic thalamus and nucleus caudatus mesially, and the nucleus
lenticularis laterally, probably giving off collateral fibres to those ganglia. Beyond
the internal capsule the fibres diverge into the general white matter of the hemi-
spheres, forming part of the system of radiating fibres known from its fan-like
arrangement as the corona radiata (Reil) or fibrous cone (Mayo), the latter tsrm
being derived from the way in which the assemblage of radiating fibres is curved
round in the form of an incomplete hollow cone as it emerges from below the
nucleus caudatus, which follows the curve of the lateral ventricle.

Although it is probable that most of the fibres of the crusta pass directly into the
medullary centre and through this to the grey cortex, without entering the basal ganglia
of the hemispheres, this has only been definitely ascertained for one or two of the
tracts of fibres which run in the crusta. The best known of these is the pyramidal
tract, which is traceable through the inner capsule (opposite the middle of the lenti-
cular nucleus) and corona radiata to the grey cortex of the ascending frontal and
ascending parietal convolutions and to the posterior parts of the first and second
frontal gyri. This is of interest in connection with the fact that physiological
experiment indicates the grey matter of these particular convolutions as especially
concerned in governing the action of the chief groups of muscles of the body (kinaes-
thetic or psycho-motor centres).

Another group of projection-fibres is the so-called direct sensory tract, which
passes from the external or lateral part of the crusta through the posterior part of
the internal capsule into the white matter of the occipital and temporal lobes of the
hemisphere (centres for special senses).

The projection-fibres from the prefrontal region pass downwards in the anterior
part of the internal capsule.

M 2

164 THE CEREBRAL HEMISPHERES.

A few of the fibres of the crusta (those nearest the inner or mesial side) do not
pass into the inner capsule and corona radiata, but are collected into the bundle
known as ansa lenticularis and pass outwards underneath the thalamus into the
nucleus lenticularis (see p. 112).

b. The fibres which pass to the cerebrum in the tegmentum, are originally
constituted by the longitudinal bundles of the formatio reticularis of the medulla
oblongata. They are reinforced as they pass upwards by sets of fibres derived from
the superior peduncle of the cerebellum, and perhaps the middle peduncle ; from the
fillet ; from the deeper parts of the corpora quadrigemina, and from the nerve- and
other nuclei in the parts which they traverse. They become lost for the most part
in the subthalamic tegmental region and in the thalamus, but on the other hand,
from the outer side of the thalamus fibres stream outwards (see p. Ill), and joining
the general system of the corona radiata, diverge to nearly every part of the hemi-
sphere. Other fibres, apparently continuous with this same system, pass from the
posterior part of the thalamus into the optic tract.

From the lower part of the thalamus anteriorly fibres emerge forming the bundle
known as the inferior peduncle of the thalamus, and curving round below the nucleus
lenticularis, pass into the white substance of the external capsule.

2. The transverse or comxnissural fibres which connect the hemispheres
together include — a. The transverse fibres of the corpus callosum. b. The fibres of the
anterior commissure.

The fibres of the corpus callosum are derived from the cells of the grey cortex,
being either the direct prolongations of their axis-cylinder processes or collaterals
passing off from the projection fibres before mentioned (fig. 20, call.). When, there-
fore, a portion of cortex is removed or destroyed, certain fibres in the corpus callosum
undergo degeneration. By this means it may be determined that the anterior portions
of the callosum contain chiefly fibres derived from the frontal lobes, the posterior
chiefly fibres from the occipital lobes, and the middle portion from the intermediate
parts of the mantle. The fibres from a limited part of the cortex are not, however,
entirely limited to one part of the callosum, but show a tendency to scatter, so that
not only similar but also dissimilar parts of the two hemispheres are connected
through this commissure (Sherrington). A certain number of projection fibres also
pass across the callosum to the other hemisphere, and then turn downwards in the
internal capsule (Hamilton). Hence, after removal of certain parts of the cortex on
one side of the brain, some degenerated fibres are found in the pyramidal tract which
is mainly connected with the other side (see p. 31).

The anterior commissure (fig. 113) is composed of a bundle of transverse fibres,
which chiefly connects the temporal lobes of the two hemispheres. The bundle is most
compact in the middle line, which it crosses at the front of the third ventricle just
in front of the pillars of the fornix : in a median section of the brain it presents an
oval section of 5 mm. long diameter, with its long axis from above down. From
this point it passes laterally as a twisted bundle of fibres curving backwards and
somewhat downwards through the ventral part of the globus pallidus, and below the
putamen of the lenticular nucleus. Its fibres then diverge in a fan-like manner
into the temporal lobe ; whether any pass by means of the external capsule to the
insula has not been satisfactorily determined.

The fibres of the anterior commissure which pass into the temporal lobe form by
far the greater part of the commissure in man, and constitute what has been termed
by Granser the pars temporalis. Besides these fibres, there are others which are
derived from the lobus olfactorius (see p. 160), and which appear to connect the
olfactory tract of one side with the hippocampal gyrus of the opposite side. These
form the pars olfadoria of Ganser : this part is very slightly developed in man.
The anterior commissure forms the segment of a circle, with the convexity

ASSOCIATION-FIBRES.

165

directed forwards. It is the principal cerebral commissure in all vertebrates below
mammals : the corpus callosum first making its appearance in the lowest mammals
and becoming developed proportionately with the increase of the mantle.

The rope-like twist of the anterior commissure is associated by Hill with a rotation of
the cerebrum, which has occurred in the course of its development (Appendix A to English
Translation of Obersteiner's " Anatomy of the Central Nervous Organs ").

3. The association-fibres which connect different parts of the same hemi-
sphere are either short or long. The short association-fibres (fibrce propria, Meynert ;

Fig. 113. — HORIZONTAL SECTION OF THE LEFT HEMISPHERE,

SHOWING THE COURSE OF THE ANTERIOR COMMISSURE.

(Testut).

1, 2, anterior commissure ; 3, pillars of fornix ; 4, lateral
ventricle, anterior horn ; 5, lateral ventricle, descending
horn ; 6, 6', corpus striatum, caudate and lenticular nuclei ;
7, thalamus ; 8, internal capsule ; 8', anterior segment of
internal capsule.

lamina arcuatce gyrorum, Arnold) (fig. 114, s.},
serve to connect adjacent convolutions, passing
round below the grey matter at the bottom of the
fissures. The long association-fibres are mostly
collected into definite bundles, which can be
traced for a considerable distance between the
bundles of comrnissural and projection-fibres, or
which run free for a certain part of their course.
The principal bundles or tracts of long associa-
tion-fibres are the following : —

(a) Superior association - bundle (superior

longitudinal fasciculus, fasciculus arcuatus, Burdach). — This consists of sagittal fibres,
which run below the grey matter of the convex surface of the hemisphere, between
the frontal and occipital lobes, and between the frontal lobe and external part of the
temporal lobe (fig. 114,/J.s.).

(b) Inferior association-bundle (temporo-occipital bundle, inferior longitudinal
fasciculus). — This is a bundle of fibres which lies close to the outer wall of the
posterior and inferior cornua of the lateral ventricle and connects the temporal and
occipital lobes (f.Li.).

(c) Anterior association-bundle (uncinate fasciculus). — Under this name is
described a white bundle, seen on the lower aspect of the hemisphere, passing across
the bottom of the Sylvian fissure at the limen insulse, and connecting the frontal
with the temporal lobe (f.u.). The fibres of this bundle expand at each extremity,
and the more superficial of them are curved or hooked sharply between the con-
tiguous parts of the two lobes, — from which circumstance it has derived the name
uncinate. Its fibres appear especially to connect the third frontal gyms with the
temporal lobe and with the anterior part of the limbic lobe.

(d) Cingulum (ci.}. — This forms the principal association-bundle of the gyrus
fornicatus, its fibres coursing immediately above the transverse fibres of the corpus
callosum, and passing from the anterior perforated space in front, curve round the
splenium of the callosum behind, and pass in the gyrus hippocampi as far as its
anterior extremity. Some of the fibres diverge, as they pass backwards, into the
white matter of the hemisphere, and probably reach various parts of the cortex.
The constitution of this bundle and its connections have been already dealt with
(see p. 158).

(e) The perpendicular fasciculus (Wernicke), which runs vertically immediately

166

THE CEREBRAL HEMISPHERES.

in front of the occipital lobe and connects the inferior parietal lobule with the
fusiform lobule (/j9.).

(/) The fornix. — This (fo.*), by means of its continuation, the fimbria (fi-\
connects the hippocampal region of the limbic lobe with the corpus albicans, which
again is connected through the bundle of Vicq d'Azyr (v.d'A.) with the thalamus

Fig. 114. — DIAGRAM OF THK ASSOCIATION-FIBKES OF THE CEREBRAL HEMISPHERE.
(E. A. S., after Meynert.)

s., short association-fibres, connecting adjacent gyri ; f.l.s., fasciculus longitudinalis superior; ci. ,
cingulum ; f.p., fasciculus perpendicularis ; f.l.i., fasciculus longitudinalis inferior ; f.u., fasciculus
uneinatus ; fo., fornix ; fi., fimbria ; v.d'A., bundle of Vicq d'Azyr.

opticus. The course and relations of the fornix have already been described
(pp. 129, 158).

The arrangement of the fibres in the white matter has been studied by H. Sachs, who finds
that the fibres in the occipital lobe (the only part as yet fully investigated by him) are arranged
in four layers or series, from within out, as follows : — 1. Those which are prolonged from the
corpus callosum (forceps major), which occupy the central parts nearest the ventricle. 2. Next
to these a layer composed of projection-fibres, passing to the internal capsule. They are finer
than the callosal fibres. 3. Another layer of larger fibres which surrounds the projection-layer,
and is composed of long association-fibres. 4. A layer of short association-fibres, nearest the
cortex. It will, of course, be understood that the peripheral layers are constantly pierced by
the fibres which are passing from the cortex to join the more centrally-situated layers.]

STRUCTURE OP THE! GREY MATTER,.

The grey matter on the convoluted surface of the cerebrum forms a continuous
layer indistinctly divided into two or three strata by interposed thin layers of paler
substance.

In examining a section macroscopically from without inwards (fig. 115, 1), we
meet with — 1. A thin coating of white matter situated on the surface, which on a
section appears as a faint white line, bounding the grey surface externally. This
superficial white layer is not equally thick over all parts of the cortical substance,
but becomes thicker as it approaches the borders of the convoluted surface ; it is

LAYERS OF CELLS IN THE CORTEX. 167

accordingly less conspicuous on the lateral convex aspect of the hemispheres, and
more so on the convolutions situated in the longitudinal fissure which approach the
white surface of the corpus callosum, and on those of the under surface of the brain.
It is especially well marked on the hippocampal gyrus, and it has been there
described under the name of the reticulated ivhite substance. 2. Immediately beneath
the white layer just described, is found a layer of grey or reddish grey matter, the
colour of which, as indeed of the grey substance generally, is deeper or lighter
according as its very numerous vessels contain much or little blood. 3. A layer,
appearing in section as a thin whitish line (line of Vicq d'Azyr, outer line of

Fig. 115. — SECTIONS OF CEREBRAL CONVOLUTIONS
(after Baillarger).

The parts are nearly of the natural size. 1, shows
the six layers ordinarily seen in the cerebral cortex when
carefully examined with the naked eye ; 2, the appear-
ance of a section of a convolution from the neighbour-
hood of the calcarine fissure.

Baillarger). 4. A second grey stratum, y. A second thin whitish layer (inner line
of Baillarger). 6. A yellowish grey layer which lies next to the central white matter
of the convolution. In some convolutions, especially those bordering on the calcarine
fissure, the line of Vicq d'Azyr is very distinct, but the inner line of Baillarger is not
visible (fig. 115, 2).

Medullated fibres radiate from the white centre of each convolution in all direc-
tions into the grey cortex, having a course for the most part perpendicular to tho
free surface. In passing through the grey substance they are arranged in bundles
about TsVoth of an inch in diameter, and thus separate the nerve-cells into elongated
groups, and give the section a columnar appearance (fig. 110). The direction of
the fibres varies according to the part of the convolution in which they occur,
whether near the summit or the base, and the radiating direction is somewhat lost
in the sulci between the convolutions, where the arched fibres which connect the
adjacent convolutions seem to obscure the radiating bundles.

Layers of cells in the cortex. — The form and arrangement of the cells vary
at different depths of a convolution, and in this way several layers are distinguished,
having more or less definite characters, but not sharply marked off from one another.
Their relation to the stratification distinguishable by the naked eye is not everywhere
clearly made out. The most common type is that which is seen in the convolutions
of the parietal lobe. In this most observers agree with Meynert in recognising five
layers as follows (fig. 116) :— -

1. Superficial or molecular layer. — This, the most external layer, is narrow, and
forms about Taoth of the whole thickness of the grey cortex. It is composed chiefly of
neuroglia, but contains some nerve-cells. A few medullated nerve-fibres occur in it,
forming a thin superficial white stratum almost immediately underneath the pia mater.

As already intimated these fibres are much more developed in the hippocampal
region than in other parts of the cortex. The layer also contains non-medullated
fibres, which ramify in it, and most of which are derived from the peripherally-
directed processes of the pyramidal cells of the deeper layer.

The neuroglia-cells of the superficial layer are mostly elongated and set perpen-
dicularly to the surface, where a principal process of each cell usually terminates in
a foot or enlargement (fig. 117).

The nerve-cells of the layer are small. They vary in shape, many being fusiform
and set parallel with the surface. Both their dendrites and their axis-cylinder
processes, which give off numerous collateral branches, are for the most part confined
to this layer. Many of them have two or three axis-cylinder processes, and these

168

THE CEREBRAL HEMISPHERES.

frequently come off from the dendrites, instead of, as is usual, from the body of the
cell (Cajal).

2. Layer of small pyramids. — This layer, of nearly the same thickness as the

Fig. 116. — SECTION OF CEREBRAL CONVOLUTION
(Meynert).

1, Superficial layer, with scattered cells ; 2, layer
of small pyramidal cells ; 3, broader layer of pyra-
midal cells, separated into columns by the radiating
nerve-fibres ; 4, narrow layer of small irregular cells ;
5, layer of fusiform and irregular cells in medullary
centre.

last, is characterized by containing a large
number of small nerve-cells, mostly pyra-
midal, with dendrites extending mainly
into the superficial layer, and an axis-
cylinder process, which starts from the
base of the cell and after giving off a few
collaterals, passes downwards to the white
centre, possibly to the corpus striatum
as a projection-fibre. Some of the axis-
cylinder processes do not, however, reach
the white matter, but end in arborisations
between the cells of the next layer.

3. Layer of large, pyramids. — The third
layer is of paler tint and much greater
thickness. It contains pyramidal branching
cells, some large others smaller, arranged
with the pointed extremities towards the
surface of the convolution, and separated
into groups by the bundles of radiating
nerve-fibres. The innermost portion of the
layer, in which the cells are larger and the
separation into groups more distinct, is
sometimes described as a separate layer.
The axis-cylinder processes of these cells
give off 7 or 8 collaterals, which become
medullated and end by ramifying in the
adjacent grey substance. The axis-cylin-
der is then continued on into the white
matter as a medullated fibre.

4. Layer of polymorphous cells. — The
fourth layer is narrower, and contains
many small, irregularly-shaped corpuscles,
with numerous dendrites and a single axis-
cylinder process. The axis-cylinder pro-
cesses of most of these cells tend towards
the white centre, but some pass peripher-
ally, and reach the molecular layer where
they become continuous with some of the
nerve-fibres of that layer.

5. Layer of fusiform cells. — The fifth
layer, of greater width than the last, and
blending more or less with it, is com-

LAYERS OF CELLS IN THE CORTEX.

169

posed of fusiform and irregular cells. The fusiform corpuscles have a definite arrange-
ment, being placed for the most part vertically at the summit of a gyrus ; but parallel to
the surface in the sulci, where they correspond in direction to the arcuate fibres passing
from one convolution to another ; they are said to be connected with these fibres.

Fig. 117. — CELLS FROM THE CEREBRAL

CORTEX, SHOWN BY GOLGl's METHOD.

(G. Retzius.)

n, n, neuroglia-cells ; p,p, pyramids ;
a,a, axis-cylinder processes of pyramids
giving off collaterals.

Beneath the last layer is the
medullary centre, with which it gra-
dually blends. The fibres of the
white substance, as they radiate into
the grey matter, become finer. They
are mostly continuous with the axis-
cylinder processes of the pyramidal
cells, the collaterals of those forming
two plexuses of medullated fibres
which lie, the one at the base of the
3rd layer, the other between this
and the 2nd layer. These plexuses
(inner and outer white plexuses of
W. Krause) are probably the cause,
of the lines of Baillarger seen with
the naked eye in a section of the
grey cortex of a fresh brain.

In the Sylvian fissure the fusi-
form cells are more abundant' than
elsewhere, and from their number
in the claustrum the fifth layer has
been termed by Meynert the " claus-
tral formation." They are also very
abundant in the amygdaloid nucleus,
which is indeed chiefly formed by a
thickening of the deepest layer of
the cerebral cortex. The cornu
ammonis on the other hand is formed
almost exclusively of the large pyra-
midal cells, and the layer in which
these occur (third layer) has, in
like manner, been termed the " for-
mation of the cornu ammonis."

The axis-cylinder processes of the
pyramids when they reach the medul-
lary centre, pass either as association-fibres to other parts of the cortex of the same
hemisphere, or as commissural fibres to the corpus callosum, and through this to the
opposite hemisphere, or as projection-fibres to the corpus striatum and optic
thalamus, or by way of the internal capsule to the midbrain, bulb and spinal cord.
The junction with fibres of the association-bundles may be T-shaped, in other words
they may bifurcate and pass in opposite directions underneath the cortex. Eventually
they turn into the cortex again and end by free arborisation amongst its cells. More-

170

THE CEREBRAL HEMISPHERES.

jb*r.f\ia*

*«

// ••

Fig. 118. — SECTION OF CORTEX OF OCCIPITAL LOBE.

1, superficial layer ; 2, layer of small pyramids ; 3 to 5, layer of large pyramids, with numerous
small "granule " cells at 4 ; 6, polymorphous cells ; 7, spindle-cells.

Fig. 119. — SECTION OF CORTEX OF TEMPORAL LOBE.
The numbers denote the same layers as in fig. 118.

Fig. 120. — SECTION OF CORTEX OF FRONTAL LOBE.
1, 2, as in fig. 118 ; 3, 4, large pyramids ; 5, polymorphous and spindle-cells.

LAYERS OF CELLS IN THE CORTEX.

171

f

r

&&%

ac-

'^2'

v- * :

""«T«r** " '" ;!.**•: "*:.'

• • »-.-. ^

ilte

Fig. 121. — SECTION OF CORTEX OF MOTOR ARKA.
The numbers denote the same layers as in fig. 120.

Fig. 122. — SECTION OF HIPPOCAMPUS MAJOR.

1, granular stratum of fascia dentata ; 2, superficial layer of cortex ; 3, stratum laciniosum ;
4, stratum radiatum ; 5, large pyramids ; 6, neuroglia-matrix (stratum moleculare) ; 7, alveus.

Fig. 123. — SECTION OF CORTEX OP GYRUS HIPPOCAMPI.
1, superficial layer ; 2, short pyramids ; 3, long pyramids.

172 THE CEREBEAL HEMISPHERES,

over, in their longitudinal course they give off collaterals here and there to inter-
mediate parts of the cortex. The commissural fibres, after passing through the
corpus callosum, have a longer or shorter course in the white matter of the opposite
hemisphere, and end by terminal arborisations in its cortex. In their course they also
give collaterals to other parts of the cortex. Some of the commissural fibres are
themselves collateral branches of the projection- fibres (fig. 20, p. 23).

The projection-fibres pass for the most part into the internal capsule. Both
before reaching this and as they pass through it they give off collaterals, some of
which enter the basal ganglia and ramify amongst the cells, whilst others pass
towards the corpus callosum. The main fibres ultimately end by arborisation in
the grey matter of the lower nerve-centres : those of the pyramidal tract amongst
the cells from which the motor nerve-fibres originate. The projection fibres are
mainly derived from the middle-sized and larger pyramids, and from some of the
polymorphous cells of the fourth layer.1

Differences of structure in different parts. — Considerable variety occurs in
different parts of the cerebral cortex in the size and regularity of shape of the nerve-
cells and in the relative thickness of the several layers. It is especially worthy of
notice that in the " psycho-motor " region, and particularly in the upper part of the
ascending frontal convolution, some of the deeper pyramidal cells are very large
(fig. 121, 4), and are arranged in more or less defined groups or nests (Betz, Bevan
Lewis). On the other hand, in the neighbourhood of the calcarine fissure, large
cells are very scanty, their places being for the most part taken by smaller ones
(fig. 118). Again, in many parts a six-laminated cortex is produced by the interca-
lation of a layer of small angular cells in the middle of the layer of large pyramids
(figs. 118, 119).

These differences in the size and arrangement of the cells in different parts of
the cortex are well illustrated in the accompanying figures (118 to 123) by Bevan
Lewis of sections from various regions.

The most remarkable differences of structure occur at the margin of the hemi-
sphere in the region of the hippocampus, and in the olfactory lobe. These will now
be specially considered.

Structure of the hippocampus major or cornu ammonis. — The hippo-
campus it will be remembered corresponds to the hippocampal fissure externally ;
this fissure separating the uncinate or hippocampal convolution below from the
fascia dentata above. The uncinate convolution (fig. 123) has the ordinary structure
of the cerebral gyri, being composed of a grey cortex and a thick white centre.
The cortex generally is, however, thin, but the superficial layer is relatively thick,
and contains many medullated fibres. The cells of the second layer are relatively
large as compared with other parts of the cortex. The cortex is prolonged around
the hippocampal fissure, forming the main part of the hippocampus (figs. 110, 124) ;
the white centre is also prolonged over the projection of the hippocampus into the
ventricle, but becomes very thin in this situation where it is known as the alveus.
It is covered by the epithelium and ependyma of the ventricle.

Above the hippocampal fissure the grey matter of the hippocampus swells out
into the notched lamina known as the fascia dentata (dentate convolution, fig. 124,
F d}. The white matter of the alveus is in like manner prolonged over this, but not
quite as far as its free border ; it becomes thickened and is continuous with the
white band known as the fimbria (Fi), which thus represents a free edge of the
medullary centre of the hemisphere.

The projection of the hippocampus (into the ventricle) is thus produced by the

1 Most of the above details relating to the destination of the axis-cylinder processes are derived from
the observations of Ramon y Cajal, made upon specimens prepared by Golgi's method.

STRUCTURE OF THE HIPPOCAMPUS MAJOR.

173

invagination of the cortex as the hippocampal fissure. According to Golgi and Sala
there is a second invagination into the fascia dentata : this must however be looked
upon as quite incomplete.

The greater part of the grey matter of the hippocampus is occupied by several
rows of moderately large pyramidal cells (fig. 122, 5 ; fig. 124, 3) with long apical
processes, which lie embedded in a neuroglia-matrix, and confer upon this, especially

7

Fig. 124. — SECTION ACROSS THE HIPPOCAMPUS MAJOR, DENTATE FISSURE, DENTATE FASCIA AND FIMBRIA

(after Henle).

Gh, part of the gyrus hippocampi or uncinate couvohition ; Fd, fascia dentata or dentate convolu-
tion ; between them is the dentate fissure ; Fi, fimbria, composed of longitudinal fibres here cut across ;
1, 2, medullary centre of the hippocampal gyrus prolonged around the hippocampus, H, as the so-called
alveus, into the fimbria ; 3, layer of large pyramidal cells ; 4, stratum radiatum ; 5, stratum laciuiosum ;
6, superficial medullary lamina, involuted around the dentate fissure ; **, termination of this lamina,
the fibres here running longitudinally ; 7, superficial neuroglia of the fascia dentata ; *, stratum
granulosum.

in its outer part, a striated aspect ; hence the name of stratum radiatum sometimes
used to distinguish this part of the layer (4), By their bases the cells rest upon the
white layer or alveus, into which their axis-cylinder processes pass, but there is in
some parts a layer of grey matter intervening (fig. 122, 6).

Superficial to the stratum radiatum, the processes of the pyramidal cells form an
arborisation, the branches of which are closely interwoven (stratum laciniosum, 5).
Superficial to this are a large number of small cells which give a granular appear-

174 THE CEREBRAL HEMISPHERES.

ance to the layer they occupy (stratum granulosuni). Superficial to this again is a
well-marked layer of medullated fibres continuous with the reticulated white substance
of the unci.nate convolution (see p. 156). It is known as the involuted medullari/
lamina (fig. 124, 6), and represents an increased development of the thin layer of
white fibres which is ordinarily found in the molecular or superficial layer of the
grey matter.

In the fascia dentata the large pyramidal cells are placed in the centre and are
irregularly arranged : they are surrounded by an incomplete ring of closely packed
small pyramidal cells (stratum granulosum, fig. 124, *), outside which is a very
broad superficial layer of neuroglia with a few scattered cells.

Minute structure of the olfactory lobe. — The peculiar structure of this part
of the brain can best be understood by a reference to its mode of development. It
is formed as a hollow outgrowth from the vesicle of the cerebral hemisphere (after-
Fig. 125. — SECTION ACROSS THE MIDDLE OF THE OLFACTORY TRACT
(Henle).

v, ventral surface ; d, dorsal ridge. From without in are seen
successively: (1) a thin superficial layer of neuroglia; (2) a (darkly
shaded) layer of transversely-cut medullary fibres, of very unequal
thickness in different parts ; (3) the central grey matter projecting up
into the dorsal ridge and here and there extending to the surface and
partially interrupting the medullary layer.

wards the lateral ventricle), and in most of the lower
animals (in which it is much more developed than in
man), it exhibits even in the adult condition a central
cavity (lined with ciliated epithelium), and in some, as
already stated, this retains throughout life its connec-
tion with the lateral ventricle. The walls of the hollow outgrowth become
thickened and differentiated into a central layer of neuroglia next to the cavity,
a well-marked intermediate layer of white substance outside this, and a peripheral
layer of grey matter surrounding the whole. In man and apes the same changes
occur, but the cavity becomes completely obliterated and in its stead we find nothing
but central neuroglia, which forms for the most part a tract flattened out laterally,
and containing but few cells. The white or medullary substance around this appears
in section in the form of a flattened ring consisting of longitudinal white fibres
(fig. 125). In the olfactory tract the peripheral layer of grey matter is very thin
and inconspicuous, so that the white substance almost everywhere shows through it,
except along the dorsal ridge where there is an accumulation of the grey substance,
extending into and partly interrupting the medullary ring (fig. 125, d). In the
bulb on the other hand this dorsal accumulation of grey matter is not seen ; but
upon the ventral side of the flattened medullary ring (fig. 126, 1, 2, 3) in place of
the thin scarcely visible layer of grey substance in the corresponding situation in
the tract, a thick layer of grey matter is found and forms indeed the greater part of
the thickness of the bulb, what was originally the central cavity being consequently
now placed near the dorsal surface. This grey matter as seen in section exhibits
the following parts (fig. 126, 4 to 8) :—

(1.) A granule layer of considerable thickness (fig. 126, 4, 5, 6) lying next to the
medullary ring, and characterised by the presence of numerous small cells, like those
found in the deeper or granule layer of the grey cortex of the cerebellum. The
layer is not entirely composed of these cells however, for there are present in addition
a number of reticulating bundles of medullated fibres which separate the " granules "
into groups, and other medullated fibres which pass vertically between the medullary
ring and the next layer. There are also a number of large nerve-cells, having for
the most part a conical shape (mitral cells, fig. 127, m.c.), the axis-cylinder processes

MINUTE STRUCTURE OF THE OLFACTORY LOBE.

175

of which pass upwards through the granule layer, while most of their protoplasmic
or dendritic processes enter the next stratum.

(2.) The layer of olfactory glomeruli (7). The remarkable bodies which

Fig. 126. — SECTION ACROSS A PART

OF THE OLFACTORY Bt'LB

(Heiile).

1, 3, layers of very fine trans-
versely cut nerve-fibres, passing
round into one another at the
side, and forming the flattened
medullary ring, enclosing the cen-
tral neuroglia, 2 ; 4, 5, 6, granule-
layer ; 7, layer of olfactory glome-
ruli, f, ft ; 8, layer of olfactory
nerve-fibres, bundles of which are
seen passing at * * to the olfactory
mucous membrane.

characterize this stratum
were first described by Ley-
dig in elasrnobranchs and
by Lockhart Clarke in
mammals. They are rounded
bodies which are formed of
a dense interlacement of
nerve-fibres derived on the
one hand from the dendrites
of the mitral cells, on the
other from the olfactory
fibres of the next layer. They also include a few small cells,\vhich are probably neuroglial.
(3.) The layer of olfactory nerve-fibres (8). This, the deepest layer of the bulb,

Fig. 127.— * DIAGRAM OF THE

CONNECTIONS OK CELLS AND
FIBRES IN THE OLFACTORY
BULB. (E. A. S.)

olf.c., cells of the olfactory
mucous membrane ; olf.n.,
deepest layer of the bulb com-
posed of the olfactory nerve-
fibres, which are prolonged
from the olfactory cells; gl.,
olfactory glomeruli, containing
arborisations of the olfactory
nerve-fibres and of the den-
drites of the mitral cells ; m.c. ,
mitral cells ; a, their axis-
cylinder processes passing to-
wards the nerve-fibre layer,
n.tr., of the bulb to become
continuous with fibres of the
olfactory tract : these axis-
cylinder processes 'are seen to
give off collaterals, some of
which pass again into the
deeper layers of the bulb ;
n', a nerve- fibre from the
olfactory tract ramifying in
the grey matter of the bulb.

olj.

consists entirely of bundles of non-medullated nerve-fibres, which here form a dense
plexus the fibres of which on the one hand pass through the perforations in the

176 THE CEREBRAL HEMISPHERES.

cribriform plate of the ethmoid bone to the olfactory mucous membrane, and on the
other hand into the glomeruli, where they ramify and form arborisations, which
interlace with those of the dendrites of the mitral cells.

The relations of cells and fibres in the olfactory bulb have recently been reinvesti-
gated by Golgi, Ramon y Cajal, v. Gehuchten, and others, by the aid of Golgi's silver
nitrate method. The result of these investigations has been to show that the
olfactory nerve-fibres take their origin in the olfactory cells of the Schneiderian
membrane, which are therefore to be regarded as peripheral nerve-cells, and that
they terminate in the arborisations already mentioned as occurring in the olfactory
glomeruli. To these same glomeruli protoplasmic processes of the mitral cells also
pass and end in arborisations which intimately interlace with those of the olfactory
fibres. (Some of the protoplasmic processes of these cells do not, however, pass to
the glomeruli, but end in free arborisations in the deeper parts of the granule layer.)
On the other hand the axis-cylinder processes of the mitral cells pass upwards from
the rounded apex of the cell, and passing between the " granules " reach the white
fibres of the medullary ring. Turning sharply backwards nearly at a right angle
they then become continuous with the fibres of the ring (see fig. 127), ultimately
reaching the olfactory tract, along which they are conducted to the base of the
brain. As they pass upwards and also in their horizontal course, they give off
collateral fibres to adjacent parts of the bulb : these collaterals end after a shorter
or longer course in free arborisations in the grey matter.

MEASUREMENTS OF THE BRAIN".

Dimensions. — The length of the cerebral hemispheres, measured from the
frontal to the occipital pole, varies in the larger proportion of cases between 160 mm.
and 170 mm. for the male brain ; and between 150 mm. and 160 mm. for the female
brain. The greatest transverse diameter of the whole brain for both sexes is about
140 mm. and the greatest vertical measurement of each hemisphere about 125 mm.
(Huschke). The brains of dolichocephalic individuals are naturally longer than
those of brachycephalic : in the latter there is a tendency to a breaking up of the
longitudinal gyri by transverse fissures, thereby increasing the amount of surface
and hence of grey cortex in proportion to the whole brain.

Extent of grey cortex. — The attempts hitherto made to measure or estimate the
relative proportions of the different convoluted parts of the cerebrum to each other
and to the degree of intelligence, either more directly or by the cranioscopic methods,
have been attended with little success. Such researches as those of Rudolph Wagner
give, however, some promise, when fully carried out, of affording more definite
results. These researches had for their object to institute an accurate comparison
between the brains of certain persons of known intelligence, cultivation, and
mental power, and those of persons of an ordinary or lower grade. As examples of
brains of men of superior intellect he selected those of Professor Gauss, a well-known
mathematician of eminence (aet. 78), and Professor Fuchs, a clinical teacher
(set. 52) ; and as examples of brains of ordinary persons, those of a woman of 29
and a workman.

The careful measurement of all the convolutions and the intervening grooves in
the four brains above mentioned was carried out by H. Wagner, by covering the
cortex everywhere with gold-leaf, and determining the extent of surface by the
amount employed. The result of these measurements is partly given in the
accompanying table, the numbers indicating square millimeters of surface.

It will be seen that although there are undoubtedly differences in the brains
examined, these are by no means so striking as might have been expected. Indeed
it may be stated that the general result of these and similar observations has been

WEIGHT OF THE BRAIN.

177

hitherto inconclusive, for although there have been observed several notable instances
in which superiority of intellect has been found to be accompanied by increased size
or complexity of the cerebral surface, in many other cases no such relation has been
noticed.

Comparative measurement of the extent of surface of the cerelral convolutions.

SURFACE OF EACH LOBE SEPARATELY.

FREE AND DEEP SUR-
FACES OF CONVOLUTIONS.

Whole
surface of
Cerebrum.

Frontal.

Parietal.

Occipital.

Temporal.

Central.

Free
surface.

Deep surface,
including sur-
face of insula.

1. Gauss

89,545
92,380
84,318

72,890

45,493
44,783
41,838
40,142

38,286
37,927
32,851
32,490

44,062
43,468
42,982
39,880

2,252
2,447
2,126
2,270

72,650
72,100
68,900
62,750

146,988
148,905
135,215
124,922

219,638
221,005
204,115
187,672

2. Fuchs

3. Woman ...
4. Workman . .

It will be seen from the above that the total surface, exposed and sunken, is
about 200,000 square mm.,, and that there is about twice as much sunken as
exposed surface. With this estimate the determinations made by subsequent
observers mostly agree. Baillarger, who dissected off and unfolded the cortex, and
then measured its whole extent, obtained only an area of 170,000 sq. mm. as
the mean of the brains thus treated. Paulier, by a modification of the method of
Wagner, obtained a result similar to that of Baillarger for the whole surface, and,
.further, found the sunken surface to measure but little more than the exposed
surface, and the extent of surface to bear no relation to the weight of the brain.
Calori measured 41 brains (Italians), and obtained the following average results (in sq.
mm.) for the total surface : — Male, brachycephalic, 243,773. Male, dolichocephalic,
230,212. Female, brachycephalic, 211,701. Female, dolichocephalic, 198,210.

Danilewsky attempted to determine the area of the whole cortex by a comparison
of the weight of the brain, its specific gravity (1038), the specific gravity of the
grey matter (1033), and white matter (1041), and the average thickness of the grey
matter, which he estimated at 2-5 mm. He obtained in this way a result of about
33 per cent, as the weight of the grey cortex, giving for a brain weighing 1324 grm.,
a total surface of 169,200 sq. mm. De Eegibus made similar calculations from
estimation not of the specific gravity but of the amount of water in the whole brain
and in its two component substances. His estimates of the total area of the cortex
of both hemispheres are higher than those of Danilewsky, varying from about
217,472 to 278,940 sq. mm. (vide Donaldson "On the Brain of Laura Bridgman,"
in the American Journal of Psychology, vols. iii.fand iv.)

Thickness of cortex. — It is clear that a measurement of surface alone without
taking into account the thickness of the cortex, may be entirely misleading as to the
amount of grey matter in the brain. This has been recognized by various observers,
who have accordingly endeavoured to form an estimate both of the average thickness
of the cortex generally, and also its thickness in special localities. The results have
been tabulated by Donaldson in the paper above referred to, and from them it
would appear that the thickness may vary from 1'55 mm. to 3'5 mm., or even
somewhat more than this, the average in normal brains being 2'9 mm. If
a section be made across a gyrus it will be found that the cortex is thickest at the
summit of the gyrus and thinnest at the bottom ofi the bounding sulci, so that it is
necessary to take a mean between these two measurements in order to arrive at the

178 • THE CEREBRAL HEMISPHERES.

average thickness for any locality. But beyond the fact that the cortex is somewhat
thinner near the hemisphere-poles, and especially the occipital pole, than in the
intermediate parts, no definite statement regarding the relative thickness of different
parts can at present be made. Females have a very slightly less thickness of cortex
than males (less than 1 per cent.), and the right hemisphere less than the left : the
difference may amount to 7 per cent. (Donaldson).

Weight. — The results obtained by Sims, Clendinning, Tiedemann and J. Eeid
showed the maximum weighb of the adult male brain, in a series of 278 cases,
to be about 1810 grammes (04 oz.), and the minimum weight about 960 grammes
(34 oz.). In a series of 191 cases, the maximum weight of the adult female brain was
1585 grammes (56 oz.). and the minimum 880 grammes (31 oz.). In a very large
proportion the weight of the male brain ranges between 46 oz. and 53 oz., and
that of the female brain between 40 oz. and 47 oz. Similar statistics have been
published by Peacock, R. Wagner, Bischofl', Huschke, Boyd, "Weisbach and others.
The mean weight at from 20 to 40 years of age was found by Boyd to be 48 oz.
(1360 grammes) for the male, and 43| oz. (1230 grammes) for the female brain.
Although many female brains exceed in weight particular male brains, as a general
fact it may therefore be affirmed that the adult male encephalon is on an average
heavier by 4 oz. or 5 oz. than that of the female (or about 9 per cent.).

The appended table, which has been compiled from the observations of E. Boyd
(Phil. Trans. 1860), shows in grammes the mean weights at different ages in the
two sexes.

MALES. FEMALES. MALES. FEMALES.

Children stillborn at term . . .
Children born alive at term .
Under 3 months

393 .
330 .
493 .
602 .
776 .
941 .
1,095 .
1,138 .
1,301 .

. 347
. 283
. 451
. 560
. 727
. 843
. 990
.1,135
. 1,154

From 14 to 20 years

1,374 .

. 1,244

From 20 to 30 years
From 30 to 40 years. . .

1,333 .

. 1,364

. 1.237
. 1.220
. 1,212

From 3 to 6 months

From 40 to 50 years

... 1,351 .

From 6 to-12 months

i From 50 to 60 years. .

1,343

1,220

From 1 to 2 years

: From 60 to 70 years. . .

1,313

. 1,208

From 2 to 4 years
From 4 to 7 years

; From 70 to 80 years

1,288 .

. 1,168

j Over 80 years
1

1,283 .

. 1,125

From 7 to 14 years

It would appear from the above that the brain is absolutely heavier between 14
and 20 years of age than at any other period of life, and that at the age of 80 it has
lost about 90 grammes, or rather more than 3 ozs., i.e., about -^ of its whole weight.

The figures obtained by Broca are somewhat higher than these, e.g., between the
ages of 30 and 35, in the male, an average of 1421 grammes (50 oz.) ; in the
female, 1269 grammes (45 oz.). According to the same statistics, the weight of the
brain attains its maximum, not before the age of 20, as found by Boyd. but between
25 and 35 in the male and a little earlier in the female. This agrees with the
results of Peacock.

The two hemispheres of the same brain, although hardly ever of exactly the
same weight, show no constant difference, the one half preponderating just about as
often as the other, and the average difference being only about 5 grammes (Braune).
There is no evidence that the right hemisphere is the heavier in left-handed people.

It has frequently been found that the brains of distinguished men have a brain -weight
above the average, sometimes markedly so, bat the rule has many exceptions. The converse
is by no means true.

The relative weight of the encephalon to the body is liable to great variation ;
nevertheless, the facts to be gathered from the observations of Clendinning,
Tiedemann, and Reid, furnish the following general result. In a series of 81 males,
the average proportion between the weight of brain and that of the body at the ages
of twenty years and upwards, was found to be as 1 to 36'5 ; and in a series of 82
females, to be as 1 to 36'46. The results of Bischoff's observations give 1 to 35'2 in

WEIGHT OF THE BRAIN.

179

the female. In these cases the deaths were the result of more or less prolonged
disease ; but in six healthy individuals dying suddenly from disease or accident,
the average proportion was 1 to 41.

The proportionate weight of the brain to that of the body is much greater at
birth than at any other period of extra-uterine life, being, according to Tiedemann,
about 1 to 5 '85 in the male, and about 1 to 6 '5 in the female. From various
observations, it further appears that the proportion diminishes gradually up
to the tenth year, being then about 1 to 14. From the tenth to the twentieth year
the relative increase of the body is most striking, the ratio of the two being at the
end of that period about 1 to 30. After the twentieth year the general average of
1 to 36 '5 prevails, with a further trifling decrease in advanced life.

Influence of stature on brain tveight. — According to J. Marshall, the proportion
of entire brain (in ozs.) to each inch of stature, is for the male sex 0'708 ; in
the female 0'688. This relative preponderance in the male is due entirely to pre-
ponderance of cerebral development ; the average stature-ratio for cerebrum alone
being 0'0619 oz. in the male per inch of stature, and (V599 oz. in the female,
whils t the stature-ratios of cerebellum, pous and medulla oblcngata, are similar in
the two sexes.

The following tables have been compiled by Marshall from the data furnished by
the observations of K. Boyd upon the brains of 1150 sane persons, viz. : — 598 males
and 552 females. They show the average weights in ozs. of the encephalon and its
several parts at certain periods of life and in individuals having certain differences
of stature : —

MALES.

STATUKE 69 INCHES AND

UPWARDS.

STATURE 68—66 INCHES.

STATURE 65 INCHES AND

UNDER.

Total number
cases.

i
}

Whole Brain.

Cerebrum.

g

1
1

6

Pons and
Med. Obi.

Whole Brain.

Cerebrum.

Cerebellum.

Pons and
Med. Obi.

Whole Brain.

Cerebrum.

Cerebellum.

Pons and
Med. Obi.

146

20—40

49-72

43-43

5-29

1

47-99

41-9

5-09

1

46-95

41-15

4-9

•9

337

40—70

48-15

42-1

5-09

•96

47-08

41-01

5-1

•97

45-74

39-88

4-96

•9

115

70—90

46-92

41-19

4-8

•93

46-

40-1

4-9

1 .

44-15

38-6

4-65

•9

598

20—90

48-40

42-34

5-09

•97

47-13

41-08

5-06

•99

45-61

39-84

4-87

•9

FEMALES.

0

STATURE 64 INCHES AND

UPWARDS.

STATURE 63 — 61 INCHES.

STATURE 60 INCHES AND

UNDER.

3

d

d

^

i

s

g

f>

j

S

xi

g

j

s

3

1 *

pa

g

pa

£

1°-

£

"3

S J

3O

E

"o

I

•§

• ?

"o

•§

nl

"3

•§

J

to 0>

H

^

o

0

PH

&

o

O

PH

F

^

u

PH

133

20—40

44-64

39-14

4-7

•8

42-98

37-23

4-85

•9

42-26

3678

4-64

•84

299

40—70

42-67

37-21

4-63

•83

42-75

37-29

4-56

•9

42-49

37-08

4-54

•87

120

70—90

41-13

35-77

4-52

•84

39-84

34-45

4-55

•84

39-59

34-36

4-36

•87

552

20—90

42-76

37-32

4-62

•82

42-37

36-84

4-64

•89

41-53

36-17

4-5

•86

N 2

180 THE CEREBRAL HEMISPHERES.

It will be seen from these that although there is an increase of brain-weight with
body-stature, this increase does not keep pace, pari passu, with the stature. That
is to say, taller persons, although they have absolutely more brain substance, have
relatively less than shorter persons. This is true for either sex. Nevertheless the
proportion of brain to the stature remains larger in the male both at the mean height
of both sexes, and at nearly corresponding heights.

Marshall further finds from a minute analysis of these results of R. Boyd, that in the case
of males of mean height, the weight in ounces of the cerebrum may be obtained by simply
dividing the number of inches of height by 1*6, or in grammes by multiplying the number of
centimetres of height by 7.

For females, the same formula as that employed for the male can be used, but the result
must be multiplied by |^.

Thus—

Height in inches
Weight in ozs. of the mean male cerebrum =

1*6

Height in inches
„ „ ., female cerebrum = — — x 5°

Weight in grammes of the mean male cerebrum = Height in centim. x 7

.. „ ,. female cerebrum = Height in centim. x 7 x ^

The weights as calculated from these formulas are found by Marshall to correspond very
nearly with the observed weights for definite statures as recorded in Boyd's tables. The
correspondence is most complete for statures near the mean, the observed weights being
slightly defective at the higher, and excessive at the lower statures.1

Most of the estimates of brain weight in different races have been obtained as
the result of measuring the cubic contents of the skull cavity (compare Vol. II.,
p. 83, and Manouvrier, loc. e»Y.).' In this way it is estimated (Davis), that the
Chinese have an average brain weight of about 1330 grammes (approaching that
of the European) ; the Sandwich islanders one of 1300 grammes ; the Malays and
North American Indians one of 1265 grammes ; the negro 1245 grammes ; the
native Australians 1185 grammes. The Hindus have also a small brain weight
(probably in relation to the small prevailing stature), viz. : 1190 grammes. Amongst
Europeans the Latin races have a somewhat less brain weight than the Teutonic and
Sclavonic races ; here also in all probability the influence of stature is apparent.

Weight of the several parts of the encephalon. — The proportionate
weight of the cerebellum (inclusive of the pons and the medulla oblongata) to that
of the cerebrum is, in the adult, as 13 to 87 (Huschke). The cerebellum is both
absolutely and relatively somewhat heavier in the male than in the female.

In the new-born infant the ratio of the weight of the cerebellum to that of the
whole brain is strikingly different from that observed in the adult. Huschke found
the weight of the cerebellum, medulla oblongata, and pons together in the new-born
infant, as compared with that of the cerebrum, to be in the proportion of 7 to 93.

Meynert found the proportions between the frontal, parietal, and conjoined
occipital and temporal lobes to be 41*5 : 2 3 '4 : and 35' 1 (in both the male and
female).

Weight of the spinal cord. — Divested of its membranes and nerves, the
spinal cord in the human subject weighs from 1 oz. to If oz. (average 30 grammes,
Schwalbe). Its proportion to the encephalon is about 1 to 43.

1 For further discussion of the proportion of stature to brain weight, the reader is referred to a
paper by le Bon in the Revue d'Anthropol. , 1879, and to one by the late Prof. J. Marshall, F.R.S., in
the Journal of Anatomy and Physiology, July, 1892.

THE DURA MATER,

181

THE MEMBRANES OF THE BRAIN" AND SPINAL CORD.

The cerebro-spinal axis is covered by three membranes, named also meninges.
They are : — 1. An external fibrous membrane, named the dura mater, which lines
the interior of the skull, and forms a loose sheath in the spinal canal ; 2. An internal
areolar and vascular tunic, the pia mater, which closely covers the brain and spinal
cord; and 3. An intermediate non-vascular membrane, the arachnoid, which lies
over the pia mater, the two being in some places in close connection, in others
separated by a considerable space.

Some authors describe only two meninges, considering the arachnoid and pia mater to
constitute one (leptomeninx), and the dura mater the other (jjachym-eninx).

THE DURA MATER.

The dura mater is a very strong dense inelastic fibrous tunic of considerable
thickness ('5 mm. or more in the cranium, less in the spinal canal). Its inner
surface, turned towards the brain and spinal cord, is smooth and lined with

Fig. 128. — SECTION THROUGH THE PLACK

OF EXIT OF A SPINAL NERVE-HOOT
THROUGH THE DURA MATER. (Key

and Retzius.)

a, bundles of the nerve-root becoming
collected into a single bundle as they
emerge ; b, dura mater ; c, arachnoid ;
d, a reticular lamella of the arachnoid
reflected along the nerve-root ; s, sub-
dural space ; s', s', subarachnoid space.

epithelium (endothelium), which
was formerly regarded as a parie-
tal reflection of the arachnoid
membrane, this having been
generally looked upon as a
serous membrane. The space
between the dura mater and
arachnoid was formerly in like
manner regarded as the sac of
the arachnoid, but is now con-
veniently termed the subdural
space. The outer surface of the

dura mater is connected with the surrounding parts in a somewhat different manner
in the cranium and in the spinal canal.

In the cranium it adheres to the inner surface of the bones, and forms their
internal periosteum. The connection between the two depends, in a great measure,
on blood-vessels and small fibrous processes, which pass from one to the other ; and
the dura mater, when detached and allowed to float in water, presents a flocculent
appearance on its outer surface, in consequence of the torn parts projecting from it.
The adhesion between the membrane and the bone is more intimate opposite the
sutures, and also at the base of the skull, which is uneven, and perforated by
numerous foramina, through which the dura mater is prolonged to the outer surface,
being there continuous with the pericranium. The fibrous tissue of the dura mater
becomes blended with the areolar sheath of the nerves at the foramina which give
exit to them.

In leaving the skull, the dura mater is intimately attached to the margin of

182 THE CEREBRAL HEMISPHERES.

the foramen magnum, and below this to the cervical vertebras as far as the third.
Above the atlas it has an orifice on each side for the passage of the vertebral artery.
Within the rest of the vertebral canal it forms a loose sheath around the cord (theca),
and is not adherent to the bones, which haVe an independent periosteum. Towards
the lower end of the canal, a few fibrous slips proceed from the outer surface of the
dura mater to be fixed to the vertebras ; one such being especially well marked at the
lower end, and seeming to join the anterior surface of the dura mater to the posterior
common ligament of the vertebrae (anterior ligament of the dura mater, Trolard).
The theca ends opposite the second sacral vertebra in the adult (see p. 6). The
space intervening between the wall of the canal and the dura mater (epidural space)
is occupied by loose fat, by areolar tissue, and by a plexus of spinal veins.

Opposite each intervertebral foramen the dura-matral theca has two openings,
placed side by side, which give passage to the two roots of the corresponding spinal
nerve. It is continued as a tubular prolongation on each nerve (fig. 128), and is
lost in its sheath. Besides this, it is connected with the circumference of the
foramen by areolar tissue.

The fibrous tissue of the dura mater, especially within the skull, is divisible into
two distinct layers, and at various places the layers separate from each other and
leave intervening channels, called sinuses. These sinuses, which have been else-
where described (Vol. II.), are channels for venous blood, and are lined with a
continuation of the endothelium of the veins. The division into two layers is most
complete at the base of the skull, in the middle fossa, and in the neighbourhood of
the cavernous sinus ; on the outer side of this the Gasserian ganglion is included in
a space (cavum Meckdii) between the two layers. Between the two cavernous
sinuses the pituitary body is received into a depression of the membrane, which
closely surrounds the organ in question, except where the infundibulum enters it.
There is further a fissure immediately over the orifice of the aquasductus vestibuli,
and here the prolongation of the membranous labyrinth of the ear, known as the
saccus endolymphaticus, is received between the two layers.

The dura mater also sends inwards into the cavity of the skull three strong
membranous processes or partitions. Of these, one descends vertically in the median
plane, and is received into the longitudinal fissure between the two hemispheres of
the cerebrum. This is the falx cerebri. The second is a sloping vaulted partition,
stretched across the back part of the skull, between the cerebrum and the cerebellum,
named the tentorium cerebelli. Below this, another vertical partition, named falx
cerebelli, of small extent, passes down between the hemispheres of the cerebellum.
Lastly, the portion of dura mater which stretches over the sella turcica, and pierced
by a small hole for the infundibulum, covers the pituitary body, is sometimes spoken
of as the operculum or tentorium of the hypophysis.

The falx cerebri (fig. 129, 1) is narrow in front, where it is fixed to the crista
galli, and broader behind, where it is attached to the middle of the upper surface of
the tentorium, along which line of attachment the straight sinus is attached.
Along its upper convex border, which is attached to the middle line of the inner
surface of the cranium, runs the superior longitudinal sinus. Its under edge is
free, and reaches to within a short distance of the corpus callosum, approaching
nearer to it behind. This border contains the inferior longitudinal sinus.

The tentorium cerebelli, or tent (fig. 129, 8), is elevated in the middle, and
declines downwards in all directions towards its circumference, thus following the
form of the upper surface of the cerebellum. Its inner border is free and concave,
and leaves in front of it a shield-shaped opening, through which the isthmus encephali
extends. It is attached behind and at the sides by its convex border to the hori-
zontal part of the crucial ridges of the occipital bone, and there encloses the lateral
sinuses. Farther forward it is connected with the upper edge of the petrous portion

STRUCTURE OF THE DURA MATER.

183

of the temporal bone — the superior petrosal sinus running along this line of attach-
ment. At the point of the pars petrosa, the external and internal borders meet,
and may be said to intersect each other — the former being then continued inwards
to the posterior, and the latter forwards to the anterior clinoid process.

The falx cerebelli (falx minor, fig. 12!), 13) descends from the middle of the
posterior border of the tentorium, with which it is connected, along the vertical

7-

Fig. 129. — THE CRANIUM OPENED TO SHOW THE FALX OF THE CEREBRUM AND TENTORIUM OP THE

CEREBELLUM, AND THE PLACES OF EXIT OF THE CRANIAL NERVES. (Sappey. ) \

1, falx ; 2, superior longitudinal sinus ; 3, concave border of the falx ; 4, inferior longitudinal
sinus ; 5, base of the falx ; 6, straight sinus ; 7, anterior part of the falx ; 8, right side of the ten-
torium cerebelli, seen from below ; 9, lateral sinus ; 10, superior petrosal sinus ; 11, inferior petrosal
sinus ; 12, posterior occipital sinus ; 13, falx cerebelli ; 14, 15, 16, 17, 18, second, third, fourth,
fifth, and sixth cranial nerves ; 19, seventh and eighth nerves ; 20, ninth, tenth, and eleventh
nerves ; 21, twelfth nerve ; 22, 23, first and second cervical nerves ; 24, upper end of the ligamentum
denticulatum.

ridge named the internal occipital crest towards the foramen magnum, bifurcating
there into two smaller folds. Its attachment to the bony ridge marks the course of
the occipital sinus or sinuses.

Structure. — The dura mater consists of white fibrous and elastic tissue, arranged
in bands and laminae, those of the two layers crossing each other obliquely for the
most part in the cranial dura mater. In the falx and tentorium the bundles
are arranged radially. It is not uncommon to find the cranial dura mater
ossified in parts : most commonly in the falx cerebri. In the spinal dura mater the
bundles have a nearly longitudinal arrangement. A layer of flattened endothelial
cells covers its inner surface, and also its outer surface between the places of
adherence to the bones and sutures. A similar layer of cells also covers both sides
of the spinal dura mater. The cranial membrane is traversed by numerous blood-
vessels which are chiefly destined for the bones, but there is a wide-meshed capillary
network with peculiar ampullary enlargements, distributed near the inner surface of
the cranial dura mater, and another network near the outer surface. The spaces
between the fibrous trabeculse contain flattened connective tissue corpuscles which

184 THE CEREBRAL HEMISPHERES.

frequently have an epithelioid arrangement : these spaces, like those of connective
tissue generally, doubtless serve for the passage of lymph. They can be injected
from the epidural space where this exists, and the injecting fluid can be forced along
them through the thickness of the dura mater into the subdural space. They can
also be filled by inserting the injecting cannula into the substance of the membrane.
Minute nervous filaments, derived from the fifth, tenth, and twelfth cranial nerves,
and from the sympathetic, enter the dura mater of the brain to be distributed
chiefly to the blood-vessels and to the bone, but partly perhaps to the membrane
itself. Nervous filaments have likewise been traced into the dura mater of the
spinal column.

The arteries of the cranial dura mater are derived from various sources ; the
principal are three in number, viz., the anterior, derived from the ethmoidal
branch of the ophthalmic ; the middle, by far the largest, a branch of the internal
maxillary ; and the posterior meningeal, a branch of the vertebral. There are also
others derived from the ascending pharyngeal and occipital arteries. Their course
and relations have already been described (see Vol. II.). Veins accompany these
arteries, but others, mostly small ones, run independently and open into the venous
sinuses. One sinus-like vein which accompanies the anterior branch of the middle
meningeal artery, communicates superiorly with the superior longitudinal sinus, and
passes inferiorly either into the veins of the orbit, or into the diploic veins, or into
the sinus cavernosus (Merkel). Communicating with the superior longitudinal
sinus from its anterior end as far back as the beginning of the occipital region are
a number of diverticula, from 0'5 to 3 cm. long, which form a series of venous
lacunae (lacuna laterales of Key and Eetzius) receiving the independent meningeal
veins, and some veins from the diploe, and are invaginated by Pacchionian granula-
tions (see p. 190). These venous lacunae are not entirely confined to the region of
the superior sinus, but some may occur in the neighbourhood of other sinuses,
especially the lateral and straight sinus.

Subdural space. — The space between the dura mater and the arachnoid, which
was formerly, when the latter was considered to be a serous membrane, known
as the cavity of the arachnoid, is now more usually known under the above title.
It is in most parts a narrow capillary cleft, containing but very little fluid, which is
probably of the nature of lymph. Its contained fluid finds exit chiefly around the
arachnoid villi (Pacchionian granulations) into the sinuses of the dura mater, but
partly by way of the lymph-clefts in the sheaths of the issuing nerves, cranial and
spinal (Key and Retzius). In animals it has been shown (by Schwalbe) that the
space is also in communication with the deep lymphatic vessels and glands of the
neck and loin. Coloured fluids injected into the subdural space are never found to
pass into the subarachnoid space, the arachnoidal limiting membrane being every-
where a closed one. Nevertheless, coloured fluids can be made to pass from the
subarachnoid space through the arachnoid, villi into the prolongations of the
subdural space which surround those villi within the venous sinuses and lacunae,
and thence into the sinuses themselves. This passage may, however, take place by
filtration.

THE PIA MATEB.

The pia mater is a delicate, fibrous, and highly vascular membrane, which
immediately invests the brain and spinal cord.

Upon the hemispheres of the brain it is applied to the entire cortical surface of
the convolutions, and dips into all the sulci, most of which thus contain a double
layer. From its internal surface numerous small vessels pass into the substance of
the brain, and hence this inner surface is very flocculent, and is named tomentum
cerebri. On the cerebellum a similar arrangement exists, but the membrane is finer,

THE VELUM INTERPOS1TUM.

185

and the double fold only distinct in the larger sulci. The pia mater also at the
transverse fissure is invaginated into the lateral ventricles and over the third
ventricle (covered however by the epithelium of those cavities), and there forms the
velum interpositum or tela choroidea superior and choroid plexuses. It is also
prolonged over the posterior wall or roof of the fourth ventricle, where it forms the
so-called tela choroidea inferior and choroid plexuses of that ventricle.

The velum interpositum. or tela choroidea superior, is a triangular fold
of pia mater, between the two layers of which arachnoidal tissue and blood-vessels
are contained, which lies immediately underneath the fornix, and can therefore only
be properly seen when this structure is cut through and raised (as in fig. 130). The
velum interpositum is then seen to cover in the third ventricle and to extend over

Fig. 130. — VIEW OF THE UPPER SUR-
FACE OF THE VELUM INTERPOSITUM,
CHOROID PLEXUSES, AND CORPORA

STRIATA (from Sappey after Vicq-
d'Azyr). f

1, fore-part of the tela choroidea
or velum iuterpositum ; 2, 2, choroid
plexus ; 3, 3, left vein of Galen partly
covered by the right ; 4, anterior
pillars of the fornix divided in front
of the foramen of Monro ; on either
side are seen small veins from the
front of the corpus caliosum and the
septum lucidum ; 5, vein of the
corpus striatum ; 6, convoluted
marginal vein of the choroid plexus ;
7, vein rising from the thalamus opti-
cus and corpus striatum ; 8, vein
proceeding from the inferior cornu
and hippocampus major ; 9, one from
the posterior cornu ; 11, fornix
divided near its middle and turned
backwards ; 12, lyra ; 13, posterior
pillar of the fornix ; 14, the splenium
of the corpus calJosum.

the adjacent upper surface of
the optic thalamus on each
side as far as the oblique
groove which marks that sur-
face (p. 110, and fig. 82).
The base of the triangle is
continuous with the general pia mater at the back and sides of the brain, the apex
ends just behind the anterior pillars of the fornix (at the foramen of Monro). Each
side of the triangle is bordered by a choroidal plexus which projects from under the
edge of the fornix into the respective lateral ventricle ; behind, these plexuses are
continued along the mesial border of the descending cornu of the ventricle, where
they are invaginated into the choroidal fissure, projecting over the fimbria ; in front
they converge, becoming gradually smaller, to the foramina of Monro, between
which they become united. From this united part two other smaller plexuses pass
backwards along the under surface of the velum interpositum, close to the middle
line in front, but diverging behind (choroid plexuses of the third ventricle).

The choroid plexuses are covered where they project into the cavities by the
epithelium of the ventricles, as is also that part of the velum interpositum which
roofs in the third ventricle. Along the choroid plexuses a prominent vein, the
choroid vein (fig. 89, p. 125), courses from behind forwards to join the vein of the
corpus striatum and form the corresponding vein of Galen at the foramen of Monro :

186 THE CEKEBRAL HEMISPHERES.

the two veins of Galen pass forwards from this point in the middle of the velum
interpositum, diverging somewhat behind, but again converging and ultimately
becoming united into a common trunk (vena magna Galeni, fig. 130, a) which opens
into the straight, sinus. In this course they receive several tributaries from the
optic thalami and other parts.

Tela choroiclea inferior. — This name has been given to the layer of pia mater
which, prolonged from the medulla oblongata, overlies the inferior half of the fourth
ventricle and is reflected at the margin of the velum medullare inferius on to the under
surface of the cerebellum. Like the velum interpositum, this also has two sets of
choroid plexuses, mesial and lateral, which are continuous with one another in front.
The mesial plexus extends forwards along either side of the middle line from the
foramen of Majendie (p. 188) to where" the tela is reflected along the edge of the
inferior medullary velum ; here the mesial plexuses are continued into the lateral
plexuses on either side, and these extend to the apertures (in the pia mater) of the
lateral recesses of the ventricle (p. 48).

On the spinal cord the pia mater has a very different character from that which
it presents on the encephalon, so that it has even been described by some as a
different membrane under the name neurilemma of the cord. It is thicker, firmer,
less vascular, and more adherent to the subjacent nervous matter : its greater
strength is owing to an external fibrous layer, which is arranged in longitudinal
glistening bundles. A fold of this membrane dips down into the anterior fissure of
the cord, and serves to conduct blood-vessels into that part. A thinner process
passes into the greater part of the posterior fissure. At the roots of the nerves, both
in the spine and in the cranium, the pia mater becomes continuous with their
connective tissue sheaths.

The pia mater of the cord is thickened by a conspicuous fibrous band, running
down in front over the anterior median fissure. This was named by Haller, linea
splendens.

Structure. — The pia mater of the cord consists of two layers, the outer one
being composed of interlaced bundles of connective tissue, which are for the most
part parallel and longitudinal, and the inner or intima of peculiar stiff bundles
bending suddenly and enclosing somewhat angular interspaces. Both surfaces of
this inner layer are covered with endothelial cells, and there is a network of fine
elastic fibres near the surfaces. On the cord pigmented cells are sometimes scattered
among the elastic fibres. The outer and inner layers are separated here and there
by cleft-like lymphatic spaces communicating on the one hand with the subarachnoid
space and on the other with the perivascular canals immediately to be mentioned.
In the pia mater of the brain only the inner of the two layers of the pia mater of
the cord is represented.

The choroid plexuses are beset with a large number of highly vascular
villous prolongations of the pia mater (choroidal villi), the larger of which are from
1 mm. to 2 mm. long, but are subdivided into smaller secondary or even tertiary
villi. Each larger villus has an afferent artery and efferent vein which open into a
capillary network lying close to the surface. The free surface of the villi and of- the
depressions between them is covered everywhere by a simple flattened or cubical
epithelium, which is ciliated in lower vertebrates, but in mammals is said to possess
cilia only in embryonic life. Each cell very commonly contains a yellowish fat
globule.

The pia mater contains great numbers of blood-vessels, which subdivide in it
before they enter the nervous substance. In the pia mater of the cord they lie
between its two layers, but in that of the brain on the surface of the membrane,
either projecting freely or covered by subarachnoid trabeculae. Further each vessel
is enclosed by a sheath composed of a more dense arrangement of the fibres of the

THE ARACHNOID MEMBRANE.

187

membrane (perivascular sheath). The diameter of the (lymphatic) canal thus
formed may be considerably larger than that of the contained vessel. A similar
sheath, derived from the pia mater, accompanies the vessel into the substance of the
brain. At its commencement it is loose and funnel-shaped and can be injected from
the subarachnoid cavity. On the cerebrum the inner layer of the pia mater is more
closely adherent to the cortical substance of the convolutions, than on the cerebellum,
where a distinct space traversed by fibres exists between the two.

Nerves. — Purkinje described a retiform arrangement of fine nerve-fibres in
the pia mater ; these are derived, according to Kolliker and others, from the
sympathetic, and from the third, fifth, sixth, facial, pneumogastric, glossopharyngeal,
and accessory nerves. Most of the fibres are destined in all probability for the
blood-vessels.

The spinal pia mater is supplied by nerves from the grey rami communicantes of
the sympathetic.

THE ABACHNOID MEMBRANE.

The arachnoid is a delicate membrane which is situated outside the pia mater,
and invests the brain and spinal cord much less closely than that membrane. It
passes over the various eminences and depressions on the cerebrum and cerebellum,

Fig. 131. — SECTION OP THE POS-
TERIOR AND LOWER PARTS OF
THE BRAIN WITHIN THE SKULL,
TO EXHIBIT THE SUBARACHNOID
SPACE, AND ITS RELATION TO

THE VENTRICLES. (After Key
and Retzius. )

The section was made in the
frozen state, the cavities having
been previously filled with injec-
tion.

1, 1', atlas vertebra ; 2, odon-
toid process of the axis, 2' ; 3,
third ventricle ; 4, fourth ventri-
cle ; C. C, corpus callo.sum ; C',
gyrus fornicatus ; C, cerebellum ;
t, tentorum ; p, pituitary body ;
c.c. , central canal of the cord ;
f.M. in the cerebello-medullary
part of the subarachnoid space, is
close to the foramen of Magendie
by which that space communicates
with the fourth ventricle.

without dipping down into
the sulci and smaller
grooves. Beneath it, be-
tween it and the pia mater, is a space (subarachnoid space) in which is a considerable
quantity of fluid (subarachnoid fluid), and in which are seen the larger blood-vessels
passing obliquely towards the brain.

The subarachnoid space is larger and more evident in some places than in
others. Thus, in the longitudinal fissure, the arachnoid does not descend to the
bottom, but passes across, immediately below the edge of the falx, at some distance
above the corpus callosum. In the interval thus left, the arteries of the corpus
callosum run backwards along that body. At the base of the brain and in the
spinal canal there is a wide interval between the arachnoid and the pia mater. In
the base of the brain, this subarachnoid space extends in front over the pons and
the interpeduncular recess as far forwards as the optic nerves, and behind it forms

188 THE CEREBRAL HEMISPHERES.

a considerable interval between the cerebellum and the back of the medulla
oblongata (fig. 131). In the spinal canal, where it surrounds the cord, it is of
considerable extent. It is occupied, in both brain and cord, by trabeculse and thin
membranous extensions of delicate connective tissue, connected on the one hand
with the arachnoid, and on the other with the pia mater. This tissue is most
abundant where the space between the two membranes is least. It is dense in the
neighbourhood of the vessels, and is continuous with the tissue of their walls. In
several places therefore the arachnoid is separated by larger intervals than at other
parts from the pia mater.

The spaces which are thereby produced are termed cisterna arachnoid ales (reservoirs of
subarachnoid fluid). They have been studied especially by Key and Retzius, and by Duret.
The principal are situated at the base of the brain. The largest (cistema cerefallo-medullaris)
lies between the middle part of the cerebellum and the medulla oblongata, and is directly
continued from the subarachnoid space of the cord. Others lie in front and at the sides of
the medulla oblongata and pons (c. pontis media s. basilari* and c.jnint-tn lateralis'), below the
interpeduncular space (c. interpeduncularis'), over the cerebral peduncles (t\c.peripedunculares),
behind the optic chiasma (c. cJviasmatis), in front of the chiasma (c. lamina? cinerete), in the
fossae Sylvii (c.c. fossa Sylvii), and over the corpus callosum (c. corporis callosi). These are
all in free communication with one another, being only partly separated by imperfect septa of
arachnoid tissue. They receive the subarachnoid clefts (flumlna) which follow the course of
the great fissures (Rolandic, Sylvian, parallel, &c.), and which themselves receive the clefts
which follow the course of the secondary and tertiary fissures (rivi and riruU of Duret).

The subarachnoid space communicates with the ventricles of the brain by means
of the foramen of Magendie (fig. 131, fM~), an opening into the lower part of the
fourth ventricle, through the pia-matral expansion (tela choroidea inferior) which
covers the ventricle ; through apertures in the lateral recesses, one on each side,
behind the upper roots of the glossopharyngeal nerve, in the pouch-like extension
of the membrane beneath the flocculus ; and perhaps also at the clefts described by
Merkel in the descending cornua of the lateral ventricles (see p. 126).

The cerebro-spinal fluid is lodged in the subarachnoid space in the meshes of
the trabecular tissue, and since this space communicates with the ventricles of the
brain, the fluid within these must be regarded as of the same nature. It differs
in many respects from ordinary lymph (compare Halliburton, Cerebrospinal Fluid,
Journal of Physiology, Vol. X.).

The spinal subarachnoid space (fig. 132, k, I) is divided by an imperfect fibrous
septum on either side termed the ligamentum denticulatum (g) into anterior and
posterior portions. As was pointed out by Magendie there also exist a sort of septum
dividing the subarachnoid space at the back of the cord (septum posticum) (c), the
relations of which have been carefully studied by Axel Key and G. Eetzius. It is a thin
membranous partition, which passes in the median plane from the pia mater covering
the posterior median fissure of the cord to the opposite part of the loose portion of
the arachnoid membrane. It is most perfect in the cervical region, being incomplete
below. It consists of numerous fine lamellae, enclosing between them small spaces,
within which run the larger blood-vessels. Subarachnoid trabeculse also connect the
nerve-roots with the inner surface of the arachnoid, and in the dorsal region fine
membranous trabeculse extend between the posterior nerve-roots and the posterior
septum. In most parts however the subarachnoid trabeculse are far less developed in
the spinal canal than in the cranium.

The nerves as they pass from the brain and spinal cord receive their perineural
covering from the pia mater, and, in addition, two looser sheaths, an outer from the
dura mater, and an inner from the arachnoid (fig. 128). Upon the optic nerve
these sheaths remain distinct and separate, so that the space which each encloses
may be injected, the outer from the subdural, the inner from the sub-arachnoid space.
On the other nerves the arachnoidal sheath soon ceases, and the single sheath eventually

LIGAMENTUM DENTICULATUM.

189

blends with both the epineurium and perineurium of the nerves. Accordingly it is
found that injection driven into either the subdural or the subarachnoid space passes
readily along the nerves even as far as the limbs. There thus exists a continuity
between the ventricles of the brain, the subarachnoid space, and the lymphatic
spaces within the nerve-sheaths.

Structure. — When examined under the microscope, the arachnoid membrane is
found to consist of distinct riband-like bundles of fine fibrous tissue interlaced with
one another. The intervals between these bundles are filled up by delicate
membranes, composed of expanded cells, the nuclei of which persist and are scattered
over the structure. Several layers of this tissue, arranged in a complex way,

Fig. 132. — SECTION OF THE SPINAL CORD

WITHIN ITS MEMBRANES (UPPER

DORSAL REGION). (Key and Retzius.)
Magnified.

a, dura mater ; b, arachnoid ; c, sep-
tum posticum ; d, c, f, subarachnoid
trabeculae, those at /, /, supporting bun-
dles of a posterior nerve-root ; g, liga-
mentum denticulatum ; h, sections of
bundles of an anterior nerve-root ; k, I,
subarachuoid space.

constitute the arachnoid mem-
brane proper. The subarachnoid
trabeculae consist of bundles of
similar fine fibrillar tissue, each
of which is surrounded by a deli-
cate nucleated sheath, also com-
posed of cells, and continuous
with the intertrabecular cell-
membranes of the arachnoid itself. The finer trabeculae when swollen by acetic
acid very frequently show the well-known ring-like constrictions. The subarachnoid
membranous expansions have a similar structure. In the spinal arachnoid the
fibril-bundles have for the most part a longitudinal direction.

Volkmann described a rich plexus of nerves in the arachnoid membrane of
certain ruminants. Kolliker failed to detect their presence ; but they have been
again described by Bochdalek, who traces them to the portio minor of the fifth, the
facial, and accessory nerves ; and they have likewise been followed by Luschka.

Ligament-am denticulatum. — This is a narrow fibrous band which runs along
each side of the spinal cord in the subarachnoid space, between the anterior and
posterior roots of the nerves, commencing above at the foramen magnum, and
reaching down to the lower pointed end of the cord (fig. 133, 9, and fig. 132, g\
By its inner edge this band is connected with the pia mater of the cord, while its
outer margin is widely denticulated ; its denticulations are attached by their points
to the inner surface of the dura mater, and thus serve to support the cord along
the sides, and to maintain it in the middle of the cavity. The first or highest
denticulation is fixed opposite the margin of the foramen magnum, between the
vertebral artery and the hypoglossal nerve (shown in fig. 182 of Vol. II.) ; the others
follow in order, alternating with the successive pairs of spinal nerves. In all, there
are about twenty-one of these points of insertion, but the lower six or seven arc less
regular. The points of the lower denticulations are prolonged into threads, and
ascend slightly to their attachments. At the lower end, the ligamentum denticu-
latum may be regarded as continued into the terminal filament of the spinal cord,
which thus connects it to the dura mater at the extremity of the sheath. The free
edge, in the intervals between the denticulations, is slightly thickened, and in many

190

THE CEEEBEAL HEMISPHERES.

parts is closely applied to the inner surface of the arachnoid, with which it is often
directly connected by fine trabeculse. The denticulations do not perforate the
arachnoid but receive from it funnel-shaped sheaths, which accompany them to the
inner surface of the dura mater (Axel Key and Ketzius).

In structure the ligament consists of white fibrous tissue, mixed with many
exceedingly fine elastic fibres. Several layers of fine connective tissue trabeculas
may be traced ; they are surrounded by sheaths, which are composed of delicate

Fig. 133. — VIEW FROM BEHIND OF THE MEDULLA OBLONGATA AND SPINAL CORD, WITH THE THECA.

(Sappey.) £.

The dura-matral sheath has been opened by a median incision and is stretched to either side. In
the upper and middle parts (A and B) the posterior nerve-roots have been removed to show the ligamentuin
denticulatum. 1 , fourth ventricle ; 2, 3, 4, cerebellar peduncles ; 5, clavus ; 6, 7, 8, roots of glosso-
pharyngeal, vagus, and accessory nerves ; 9, points of ligamentum denticulatum ; 10, line of entrance of
posterior roots into spinal cord ; 11 (in B), posterior median fissure; 12, ganglia ; 13, cut anterior roots ;
14, mixed nerve ; 15, 16, filum terminate ; 17, cauda equina.

nucleated cells, and here and there expand into membranes. Its tissue is continuous
on the one hand with that of the pia mater, and at the apices of the denticulations
with that of the dura mater.

Glanclulce Faccliionii or arachnoidal villi. — Upon the external surface of the
dura mater, in the vicinity of the longitudinal sinus, are seen numerous small pulpy
looking elevations, generally collected into clusters, named glands of Pacchioni
(fig. 134). The inner surface of the calvaria is marked by little pits, which
receive these prominences. Similar excrescences are seen on the internal surface of
the dura mater, and upon the pia mater on each side of the longitudinal sinus, and
also projecting into the interior of that sinus (s). Occasionally they are found
also in other situations.

On a careful examination of the connections of these bodies it will be found that

GLANDULE PACCHIONII OR ARACHNOIDAL VILLI.

191

the elevations found on the outer surface of the dura mater and within the
longitudinal sinus, in no instance take origin in those positions, but that they are
grape-like bodies which are attached more deeply, and in their growth have
invaginated the dura mater. Their precise origin and nature were long the subject
of conflicting opinions, but it has been satisfactorily shown by Luschka that they are
villi of the arachnoid. On each side of the sinus, and communicating with it, are
large venous spaces in the dura mater (lacunae laterales, see p. 184) ; into these the
villi project even in new-born animals, and those which appear to perforate the dura

Fig. 134. — SECTION OF THE UPPER PART OF THE BRAIN AND MENINGES TO SHOW THE RELATIONS OP
THE ARACHNOIDAL VILLI. (Key and Retzius.) Magnified.

c.c., corpus callosum ; /, falx cerebri ; s.a., subarachnoid space, pervaded by a network of fine
trabeculse ; from it the fungiform villi are seen projecting into the lateral lacunae of the dura mater.
Some are projecting into the superior longitudinal sinus, *.

mater and appear on the surface have their inner parts in these spaces. Each villus
is covered by a membrane, continuous with the arachnoid. Outside this is another
fine membranous sheath, derived from the dura mater, and the interval between the
two is continuous with the subdural space. Within the villus is a spongy trabecular
tissue, continuous with the subarachnoid tissue, and of similar structure (Key and
Retzius).

Fluid injected into the subarachnoid space passes freely into the Pacchionian
bodies, and is found after a time to filter through their walls and thus to get into
the subdural space, although there does not appear to be any open communication
between the interior of these bodies and the prolongation of the subdural space
which surrounds them. Moreover, if the injection is continued it can be driven
even into the interior of the venous sinuses and lacunas which are found in connection
with them, especially into the superior longitudinal sinus, into which the arachnoidal
villi project. So that these villi seem to afford a means of passage of the cerebro-
spinal fluid from the subarachnoid space into the venous sinuses, when the fluid
pressure in the subarachnoid space becomes from any cause increased above
the normal.

BLOOD-VESSELS OP THE BRAIN AND SPINAL CORD.

Blood supply of the spinal cord. — The arteries of the spinal cord are (1) the
anterior spinal, double above where it is derived from the vertebrals, but single and
median below where it is reinforced by a series of small vessels derived from the
vertebral, intercostal, lumbar, and other arteries, and passing to the cord along

192

THE CEREBRAL HEMISPHERES.

the anterior roots, and (2) the paired posterior spinal arteries, similarly derived from
the vertebrals, intercostals, and other arteries, and running just in front of the line
of attachment of the posterior roots. Another small longitudinal anastomotic chain
formed by branches of the posterior spinal runs along just behind the line of the
posterior roots.1 The branches of these vessels ramify in the pia mater investing the
cord, communicating with one another to form transverse anastomoses, and from the
main vessels and their ramifications vessels pass in to supply both the grey and
white substance.

The small entering branches may be described as forming two systems, a
centrifugal and a centripetal. The first is composed of a series of arterioles,
(central arterioles, Ross), 200 to 300 in number, which pass from the anterior spinal

Fig. 135. — SEMIDIAGRAMMATIC REPRESENTATION

OF THE ARTERIES IN THE INTERIOR OF A
SEGMENT OF THE SPINAL CORD. (Ober-

steiner. )

a.s.a., anterior spinal artery; c, a central
arteriole ; a, an anastomotic branch uniting it
with another arteriole of an adjacent segment ;
C'l., branch to Clarke's column ; a.p.f., artery
of posterior fissure ; p.m.a., posterior mesial
artery; a.p.e., artery of posterior cornu ; p.s.a.,
branch of posterior spinal artery passing into
gelatinous substance ; p, other peripheral or
centripetal arterioles passing through white
substance of cord.

artery into the anterior median fissure,
penetrating to the anterior commissure.
Here each one passes either to the right
or left, and divides into smaller arteries
and capillaries for the central parts of
the corresponding crescent of grey
matter; but a considerable ascending
and descending ramuscule is also given
off, and these overlap in their distri-
bution the corresponding longitudinal
branches of the adjacent central arte-
rioles. Although mainly distributed to the central parts of the grey matter the
central arterioles may also send branches to join the capillaries of the white matter.
The second or centripetal set has a converging or radial arrangement, passing in
from the periphery. Some of these simply form capillary loops, which supply the
superficial layers of the cord. Others are distributed to the white matter, where they
form comparatively large-meshed longitudinal plexuses. But the most considerable
of the centripetal arteries penetrate to the grey matter, and pour their blood into the
close capillary network which pervades it, supplying the parts not served by the
centrifugal vessels. The capillaries of the substantia gelatinosa are less numerous
than in the rest of the grey matter, and their meshes are mostly longitudinal.

Special mention may be made of a series of small median arterial branches which
enter the posterior fissure, penetrating in it to the posterior commissure, and giving
off branches which supply the adjacent parts of the posterior white columns and
Clarke's column, where this is found ; and of the vessels which enter the grey matter
with the bundles of the anterior and posterior nerve-roots, and are distributed to the
corresponding cornua. It would appear however that no one part is supplied by only
one set of arterioles, nor is any one set of arterioles confined in its distribution to

1 For the origin and course of the spinal arteries see Vol. II., pp. 421 and 422.

BLOOD-SUPPLY OF THE BttAIN.

any one white column or group of cells in the grey matter. At the same time it
should be noted that within the cord itself (as within the brain), all the arteries are
" terminal arteries," in Cohnheim's sense, that is to say, they do not anastomose with
other arteries, but each one terminates in its own capillary area, and supplies no
other. There is however much variation in the extent of the capillary area supplied
by any of the arterial branches, and no definite statement can be made concerning
the exact region supplied by any set of arterioles (Kadyi).

The origin and course of the veins of the spinal cord have been described
in Vol. II., pp. 533, 534. The most considerable are two longitudinal median
vessels, one running along the anterior median fissure along with the anterior spinal
artery, and another over the posterior median fissure, unaccompanied by any
considerable artery. Both of these median veins have a tortuous course, and the
posterior one is frequently broken up into a kind of venous plexus, with longitudinal
meshes, which extends over the whole posterior surface of the cord. There is also
a less perfect lateral anastomotic chain lying behind the line of exit of the anterior
nerve roots. All these vessels communicate freely with one another by lateral offsets.
They receive the venous blood from the cord on the one hand, and on the other hand
carry it away by veins which accompany, at frequent intervals, the nerve roots. In
the upper part they join the veins of the cerebellum and pons, and the venous
sinuses around the foramen magnum. Within the cord their branches anastomose
frequently. The vein accompanying the anterior spinal artery receives, like that
vessel, very numerous tributaries from the anterior median fissure (central venules) :
these carry away a large part of the blood from the grey matter ; the peripheral
venules, which enter the veins of the pia mater which covers the general
surface of the cord, chiefly carry away the blood from the capillaries of the white
matter.

Blood-supply of the brain. — The origin and course of the vessels which supply
the brain have already been described in the section Angeiology, Vol. II. pp. 411 to
415 (arteries), and 519 to 524 (veins). In passing to their distribution the several
arteries, having passed across the subdural space, enter the subarachnoid space and
then divide and subdivide into branches, which, in their further ramification on the
nervous centres, are supported by the pia mater, and, it may be remarked, are more
deeply placed in the various fissures and sulci than the small veins, which do not
accompany the arteries, but pursue a different course, and are chiefly seen upon the
surface of the pia mater. From the arteries in the pia mater of the hemispheres
very numerous small branches pass vertically into the grey matter of the convolutions.
Most of these (cortical arteries) at once break up into a close plexus of capillaries for
the grey matter ; but others (medullary arteries), larger but less numerous, pass
through the grey matter, giving off only a few small branches to it, and penetrate
for some distance into the medullary centre, where they divide into a long-meshed
capillary network. The smaller branches of arteries anastomose together to a
certain extent in the pia mater before penetrating into the superficial grey matter
(Huebner), but the branches which pass to the chief ganglia, such as the optic
thalamus or corpus striatum, do not anastomose with one another.

Moreover, it is to be observed that, whilst the main branches of the arteries are
situated at the base of the brain, the principal veins tend towards the upper surface
of the hemispheres, where they enter the superior longitudinal sinus, most of them
looping forwards as they pass into the sinus, and often entering the dura mater
a short distance from the sinus, but more usually having a free course, sometimes
of considerable length, through the subarachnoid space in passing from the pia into
the dura mater. The veins of Galen, coming from the lateral ventricles and choroid
plexuses, run backwards to the straight sinus, in the subarachnoid tissue which lies
between the two layers of the velum interpositum.

VOL. III. O

194 THE BRAIN.

It may be convenient here to recapitulate the sources of the blood supply to the
several parts of the encephalon.

The medulla oblongata and pons Varolii are supplied by branches from the

Fig. 136. — THE ARTERIES OF THE BASE OF THE CEREBRUM. (G. D. T., after Duret, and from nature.)

On the left side of the brain the temporal lobe is cut away so as to open the inferior and posterior
horns of the lateral ventricle. The mid-brain is divided close above the pons and the posterior cerebral
arteries are cut at their origin from the basilar.

Central arteries (to the basal ganglia) : am, antero-mesial group arising from the anterior cerebral ;
al, antero- lateral group, from the middle cerebral ; pm, pi (on the optic thalamus), postero-mesial and
postero-lateral groups, from the posterior cerebral.

Choroidal arteries: a ch, anterior, from the internal carotid ; p ch (on the splenium), posterior, from
the posterior cerebral.

Peripheral arteries: 1, 1, inferior internal frontal, from the anterior cerebral ; 2, inferior external
frontal ; 3, ascending frontal ; 4, ascending parietal, and 5, temporo-parietal, from the middle cerebral ;
6, anterior temporal, 7, posterior temporal, and 8, occipital, from the posterior cerebral.

anterior spinal, the vertebral, the basilar, and the posterior cerebral arteries. The
branches enter the pons and medulla oblongata in two sets, lateral or radicular

BLOOD-SUPPLY OF THE BRAIN. 195

(following the roots of the nerves), and median, — the latter passing in the raphe
to the grey matter on the posterior surface. The valve of Vieussens and the
superior peduncle of the cerebellum receive twigs from the superior cerebellar
arteries. The choroid plexuses of the fourth ventricle are supplied by the inferior
cerebellar arteries.

Cerebellum. — The under surface is supplied by the inferior cerebellar arteries
from the vertebral, and the anterior from the basilar. The upper surface is supplied
chiefly by the superior cerebellar arteries from the basilar : its posterior portion
from the inferior cerebellar.

The crura cerebri derive their blood supply from the posterior communicating
and the posterior cerebral arteries. Branches of the latter, and also others from the
end of the basilar, enter the posterior perforated space.

The corpora quadrigemina and corpora genie ulata are both supplied by the
posterior cerebral artery, but branches of the superior cerebellar arteries pass to the
inferior corpora quadrigemina.

The optic thalamus is supplied above and on the outer, inner and posterior

Fig. 137. — CORTICAL DISTRIBUTION OP THE MIDDLE CEREBRAL ARTEKY. (G. D. T., after Charcot.)

Diagrammatic.

CENT., antero-lateral group of central arteries : 1, inferior external frontal artery ; 2, ascending
frontal artery ; 3, ascending parietal artery ; 4, parieto-temporal artery.

sides by branches of the posterior cerebral artery, but its anterior and inner
portion receives twigs from the posterior communicating arteries of the circle of
Willis and its anterior and outer portion from the middle cerebral.

Cerebral hemispheres.— Frontal lobe. — The superior frontal and anterior two-
thirds of the middle frontal convolution, with the upper extremity of the ascending
frontal, are supplied by the anterior cerebral. The inferior frontal convolution, the
posterior extremity of the middle frontal, and the greater part of the ascending
frontal convolutions are* supplied by the middle cerebral. The orbital surface is
supplied, outside the orbital sulcus, by the middle cerebral : within that sulcus
(including the olfactory bulb) by the anterior cerebral.

Parietal lobe. — All the convolutions of the parietal lobe are usually supplied
by the middle cerebral artery.

Occipital lobe. — This lobe is supplied entirely by the posterior cerebral artery.

Temporal lobe. — The superior and upper parts of the middle temporal convo-

o 2

196

Fig. 138. — DIAGRAMS SHOWING THE AREAS OF CORTICAL DISTRIBUTION OF THE ANTERIOR, MIDDLE, AND

POSTERIOR CEREBRAL ARTERIES RESPECTIVELY. (E. A. S.)

A, lateral ; B, mesial aspect ; o, basal aspect.

The area supplied by the middle cerebral frequently extends to the upper border of the hemisphere
in the region of the parietal lobe, and therefore somewhat further than is represented in A.

BLOOD-SUPPLY OF THE BRAIN.

197

lutions are supplied by the middle cerebral artery. The lower portion of the lobe
by the posterior cerebral.

Inner surface of the hemispheres. — The whole anterior and upper portion, as far
back as the parieto-occipital fissure, is supplied by the anterior cerebral artery ; the
cuneate lobule and the occipito-temporal region by the posterior cerebral.

The distribution of arteries to the several parts of the cerebral cortex is
illustrated in the accompanying diagrams (fig. 138).

The corpus callosum is chiefly supplied by the anterior cerebral.

The grey substance at the base of the cerebrum is supplied by small twigs from
the adjacent vessels of the circle of Willis, or from the roots of the cerebral
vessels which pass off from the anastomosis.

Central parts — corpus striatum. — Both nucleus caudatus and nucleus lenticularis

are supplied almost exclusively by the middle cerebral artery, the numerous branches
to these parts entering through the foramina in the anterior perforated space
(fig. 136). They are divided by Duret into lenticular, lenticulo-striate, and lenticulo-
optic (lenticulo-thalamic). These pass directly to their destination without anasto-
mosing with one another, and traverse the zones of the lenticular nucleus and the
internal capsule, to terminate finally in the caudate nucleus and optic thalamus
(fig. 139). One in particular of the lenticulo-striate arteries which passes through
the outer part of the putamen is very frequently the seat of haemorrhage, and
it has accordingly been termed by Charcot the " artery of cerebral haemorrhage "
(fig. 139, z).
The anterior part of the caudate nucleus is also supplied by the anterior cerebral,

198 THE BRAIN.

and its upper surface receives fine twigs from the lateral choroidal branch of the
posterior cerebral.

The choroid plexuses of the lateral ventricles are supplied (1) by the anterior
choroid branch of the internal carotid which passes obliquely backwards and out-
wards, and enters the choroid plexus at the anterior end of the descending cornu,
supplying two-thirds of the plexus of the lateral ventricle ; (2) by the postero-
laterat choroid artery, a branch of the posterior cerebral, which supplies the
remaining third of the plexus. The choroid plexus of the third ventricle is
supplied by a branch (postero- mesial) of the posterior cerebral. The velum

Fig. 139. — FRONTAL SECTION OF THE BBAIN, SHOWING THE MODE OF ORIGIN AND DISTRIBUTION OF

THE LENTICULO-STRIATE AND LENTICULO-THALAMIC ARTERIES. (E. A. S..) Diagrammatic.

c.c., corpus callosum ; fo., fornix ; a.c. , anterior commissure ; a, corpus albicans ; i, infundibulum ;
ch., chiasma ; tr., optic tract; v.L, lateral ventricle; n.c., nucleus caudatus ; n.L, nucleus lenticu-
laris ; th., thalanms ; c.i., internal capsule ; d., claustrum ; am., nucleus amygdalae ; above x, artery
of haemorrhage. (The plan of the section is copied from Merkel. )

interpositum is also supplied by the two last-named branches of the posterior
cerebral. The parts in the quadrilateral space at the base of the brain including
the chiasma, the infundibulum and the corpora mamillaria receive branches directly
from the circle of Willis.

For further details on the subject, which derives importance from the relation
of different local pathological conditions to the vascular distribution, the reader is
referred to a series of articles by Duret in the Archives de Physiologic for 1873 and
1874, to a paper by Huebner in the Med. Centralblatt, 1872 ; and to a work
entitled " Die luetische Erkrankung der Hirnarterien," Leipzig, 1874, by the same
author.

Lymph-paths of the brain and spinal cord. — Neither the brain nor the spinal cord
possesses true lymphatic vessels. The lymph finds its way out of these organs by means of
perivascular spaces in the tunica adventitia of the blood-vessels ; these perivascular spaces
communicate with the subarachnoid space at the surface of the brain and cord (Key and Retzius).

RECENT LITERATURE OF THE BRAIN. 199

RECENT LITERATURE OP THE BRAIN.'

GENERAL LITERATURE.

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1886.

Dalton, J. C., On the form and topographical relations of the corpus striatum, Brain, vol. Hi.,
1880 ; Topographical Anatomy of the Brain, Atlas, 1882.

Edinger, L., Unttrsuchungen uber die vergleichende Anatomic des Gehirns : I. Das Vorderhirn ;
II. Das Zwischenhirn, Frankfurt-a. -M., 1892 ; Zwolf Vorlesungen, &c., 3rd edition, 1892.

Ferrier, The functions of the Brain, 2nd edition, 1886.

Gavoy, L 'encephale, structure it description iconographique, 1886.

Gowers, W. R., Diseasfs of the Nerrous System : Vol. L, Diseases of the Spinal Cord; Vol. II.,
Diseases of the Brain.

Henle, J., Handbuch der Ntrvenlehre, Braunschweig, 1879.

Hill, A., The plan of the central nervous system, Cambridge, 1885.

Luys, J., Recherches sur le systeme nerveux cerebro-spinal, Paris, 1865 ; Iconographie photo-
graphiquc des centres ntrveux, 2me edition, Paris, 1890.

Mendel, Gehirn, Anatomisch, Eulenburg's Real-Encylop. der Gesammt. Heilkunde, vii. , 1886.

Meynert, Psychiatry, translated by £achs, 1885; Article "Brain" in Strieker's Histology,
Sydenham Society's translation, vol. ii.

Obersteiner, H., The Anatomy of the Central Nervous Organs in health and in disease, trans,
by A^ex. Hill, London, 1890, and German 2nd edition, 1892.

Spitzka, E. C., Architecture and Mechanism of the Brain, Journ. of Nerv. and Ment. Diseases,
1878 et seq.

Schwalbe, G., Lehrbuch der Neurologic, 1881.

Testut, L., Trait6 d' anatomic humaine. T. ii. fasc. 2. Neurologic. Paris, 1891.

Wernicke, C., Lehrbuch der Gehirnkrankheitcn, vol. i., 1881.

Wilder, B. Q., Article "Brain — Gross or Macroscopic Anatomy," Reference Handbook of the
Medical Sciences, viii., 188i.' ; and "Malformations of Brain," Ibid.

Wundt, W., Grundziige der physiologische^ Psychologic, Leipzig, 1880.

SURFACE MORPHOLOGY OF THE HEMISPHERES.

Bastian, H. C., and Horsley, V., Arrest of development of the upper limb in association with
an extremely small right ascending parietal convolution, Brain, vol. iii., 1880.

Beer, On the development of the Sylvian fissure in the human embryo, Journal of Anat. and Phys.,
1890.

Beevor, C. E., and Horsley, V., A minute analysis of cortical centres in the monkey, Phil.
Trans., 1887 and 1888.

Benedikt, M., Der Raubthiertypus am menschlichen Gehirne, Vorlaufige Mittheilung, Centralblatt
fur die medieinischen Wissenschaften, 1876; Der Hinterhauptslappen der Sdugethiere, Ibid., 1877;
Anatomische Studic-n an Verbrecher-Gehirnen, Wien, 1879; Zur Frage'des Vierwindungstypus,
Centralblatt f. d. med. Wissenschaften, 1880 ; Beitrage zur Anatomic der Gehirn- Oberfldche, Wiener
Jahrbucher, 1888, s. 39 ; Ueber die Fissura calloso-marginalis, Verh, d. internat. Congress, Berlin,
1890, Bd. ii. ; Some points on the sur face- anatomy of the brain, Journ. of Anatomy, vol. xxv., 1891.

Bischoff, Th. L. W., Die Grosshirnwindungen des Menschen, Abhandlungen der k. bayer.
Akademie d. Wissensch., Munchen, 1868 ; Ueber das Gehirn eines Gorilla und die untere oder dritte
Stirnwindung, Sitzungsberichte der k. bayer. Akademie der Wissenschaften, Munchen, 1877.

Broca, A., Anatomic descriptive des cir -convolutions ce're'brales, Gaz. hebdom., T. xxxviii., 1891.

Broca, P., Anatomic comparee des circonvolutions ce'rebrales. Le grand lobe limbiqueet lascissure
Hmbique dans la serie des mammiferes, Revue d'anthrcpologie, 1878 ; Recherches sur les centres olfactifs,
Ibid., 1879 ; Description elementaire des circonvolutions cMbrales de Vhomme d'apres le cerveau
sche'matiquc, Ibid., 1883 and 1884 ; Memoircs sur le cerveau de Vhomme et des primates, Paris,

Cunningrham, D. J., The complete fissures of the human cerebrum, and their significance in
connection with the growth of the hemisphere, Journ. of Anatomy and Physiology, xxiv., 1890 ; On
cerebral anatomy, Brit. Med. Journ., Aug., 1890 ; The surface anatomy of the primate cerebrum,
Cunningham Memoirs of the Royal Irish Academy, No. VII., 1892.

Debierre, C., Sur les anomalies des circonvolutions du cerveau de Vhomme, Comptes rendus de la
societe de biologic, 1891.

Dercum, A note on the " pli de passage inferieur interne" in the human brain, Journ. of nerv.
and mental disease, 1889 ; A description of two Chinese brains, Ibid.

Donaldson, H. H., Nervous System. Report of 6 lectures on cerebral localization delivered in
Boston, Amer. Journ. of Psychol. , vol. iv., 1891.

Duval, M., La corne d' Amman, Arch, de neurol., 1881-2.

Dwigrbt, T., Remarks on the brain of a distinguished man, Proc. Amer. Acad., vol. 13, 1887,

1 For literature of Cerebellum, see p. 95 ; for Mid-brain and Interbrain, see p. 120.

200 RECENT LITERATURE OF THE BRAIN.

Eberstaller, O., Zur Oberflachenanatomie der Grosshirn- Heminphdre, Wiener med. Blatter,
1884 ; Zur Anatomic u. Morphol. der Insula Reilii, Anat. Anz. ii., 18b7 ; Das Stirnhirn, &c. , 1890.
Eeker, A., Die Hirnwindungen des Menschen, Braunschweig, 1869 and 1883.
Fraser, A., A guide to operations on the brain, London, 1891.

Giacomini, C., Varietes des circonvohitions cerebrales chez I'homme, Arch. ital. de biologic, t. i.,
1882 ; Beiiderella dell' uncus dell' hippocampo, <fcc., Giorn. d. R. accad. d. Torino, 1882, and in Arch,
ital. de biologic, t. ii. , 1882; Fascia dentata del grande hippocampo, Ibid. ; Varieta d. circonvol.
cerebrali nelluomo, 1884 ; Guida atto studio delle circonvoluzioni cerebrali deWuomo. 1884 and 1891 :
Sur le cerveau d"un Chimpanze, Arch. ital. de biologic, vol. 3, 1890, and in Atti d. R. accad. d. sci.
di Torino, 1889 ; Les cerveaux des microcephales (avec 1 pi.), Arch. ital. de Biol., t. 15, 1891 ; /
cervelli dei microcefali, Torino, 1890.

Gowers, W. B,., The brain in congenital absence of one hand, Brain, vol. i., 1878.
Gratiolet, Mimoire sur les plis cerebraux de I'homme et des primates, Paris, 1854.
Guldbergr, Bidrag til Insula Reilii's Morphologie, Christiania, 1887, and Anat. Anzeiger, 1887.
Hatch, J. lieffingrwell, Some studies upon the Chinese Brain, Intern. Monatsschr. f. Anat. u.
Phys., Bd. viii., 1891.

Herve, La circonvolutwn de Broca, These, Paris, 1888.

Heschl, Die Tiefcnwindungen d. menschl. Gehirns, <£•<;., Wiener med. Wochenschr., 1877; Ue.
d. vordere quere Schldfenwindung, Wien, 1878.

Horsley, V., and Schafer, E. A., A record of experiments upon the functions of the cerebral
cortex, Phil. Trans., vol. 179, 1888.

Howden. R.., Variations in the hippocampus major and eminentia collateralis in the human
brain, Journ. of Anat. and Phys., xxi., 1888.

Huxley, T. H., On the brain of Ateles paniscus, Proc. Zool. Soc., 1861.

Jelg-ersma, G., Ueber den Ban des Sdugethiergehirns, Morph. Jahrb., 1888 ; Das Gehirn ohne
Balken, ein Beitrag zur Windungstheorie, Neurol. Centralbl. ix. , 1890.

Jensen, J. , Die Furchen und Windungen der menschlichen Grosshirn-Hemisphdren, Zeitsch. f.
Psychiatric, 1871.

Kowalewsky, P., Das Vcrhdltniss des Linsenkerns zur Hirnrinde, Sitzungsb. cl. Wiener Akacl.
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Lussana, Ph., Circumvolutionum cerebralium anatomes humana et comparata, Editio 2da.
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Pansch, A., Die Furchen und Wulste am Grosshirn des Menschen, Berlin, 1879 ; Ueber die
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Parker, A. J., Cerebral convolutions of the negro, Proc. of the Philadelphia Academy, 1878.
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Pitres, A. , Sur les atrophies partielles des circonvohitions cerebrales, consecutivement aux ampu-
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Ketzius, G., Notiz u. d. Windungen an der unteren Fldche des Splenium corporis callosi, Arch,
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Richter, Ueber d. Entstehung d. Grosshirnwindungen, Arch. f. path. Anat., 1887.
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Ruding-er, N., Vorlaufige Mittheilungen iiber die Unterschiede der Grosshirnwindungen nach
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Schnopfhagren, F., Die Entstehung der Windungen des Grosshirns, Jahrb. d. Psych., ix.,
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Seitz, J., Zwei Feuerlander-Gehirne, Zeitschrift f. Ethnologic, Berlin, 1886.
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Trolard, De I'appareil nerveux central de I'olfaction, Arch, de neurol., 1890, 1891.
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Vanhersecke, G., La morphologic des circonvohitions cerebrales, Lille, 1891.
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RECENT LITERATURE OF THE BRAIN. 201

Weisbach, A., Die Supraorbital-windungen des menschlichen Gehirns, Wien. med. Jahrb., 1870.

Wilder, Burt Q-., Human cerebral fissures, their relations and names and the methods of
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Zilgrien, Etude d'un cerveau sans circonvolutions chez un enfant de onze ans et demi, Journal de
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Zuckerkandl, E., Beitrage zur Anatomic des menschlichen Korpers, IV. Ueber den Einfiuss des
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COURSE OF WHITE TRACTS AND COMMISSURES.

Bechterew, W. v., Zur Frage u. d. dusseren Associationsfasern der Jfirnrinde, Neurol.
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Beevor, C. E., and Horsley, V., Arrangement of the excitable fibres in the internal capsule of
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Beevor, C. E., On the course of the fibres of the cingulum, and the posterior parts of the corpus
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Bruce, A., On the absence of the corpus callosum in the human brain, Proc. Roy. Soc. of
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Dejerine, Contribution a I' etude de la degeneretence des fibres du corps catteux, Soc. de Biologic,
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Edingrer, L., Zur Kenntniss des Faserverlauf im Corpus striatum, Neurol. CentralbL, 1884.

Flechsig-, P., Die Leitungsbahnen im Gehirn u. Rilckenmarlc, Leipzig, 1876 ; Plan des menschl.
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France, E. P., On the descending degenerations which follow lesions of the gyrus marginalis and
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Ganser, Ueber die vordere Hirncommissur der Sdugethiere, Arch, fur Psychiatric, vol. ix., 1878.

G-udden, B. v., Gcsammelte und hinterlassene Arbeiten, 1889.

Hamilton, D. J., On the corpus callosum in the adult brain, Journal of Anatomy, vol. xix., 1885 :
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Honegrgrer, S., Vergleichend-anatwn. Untersuchungen uber den Fornix, tfcc., Zurich, 1891.

Hdsel (u. Flechsig:), Die Centralwindungen ein Centralorgan der Hinterstrange, Neurol.
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Lang-ley and G-riinbaum, On the degenerations resulting from removal of the cerebral cortex and
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Luys, Nouvelles rechcrches sur la structure du cerveau et agencement des fibres blanches cerebrales,
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1886.

Sachs, H., Das Hemisphdrenmark des menschlichen Grosshirns, I. Der Hinterhauptlappen,
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Sherriugton, Nerve tracts degenerating secondarily to lesions of the cortex cerebri, Journ.
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Zacher, Beitr. z. Kenntniss des Faserverlaufs im Pes Pedunculi, sow. u. d. corticalen Beziehungen
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Zuckerkandl, Ue. d. Riechbundel des Cornu Ammonis, Anat. Anzeiger, iii., 1888.

MINUTE STRUCTURE.

Berkley, H. J., The meduttated cortical fibres, <kc., Medical Record, New York, 1892.

Betz, Ueber diefeinere Struktur d. menschl. Gehirnrinde, Med. CentralbL, 1881.

Blumenau, !•., Zur Entwickl. u. feineren Anatomie des Hirnbalkenit, Arch. f. mikr. Anat.,
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voluciones cerebrales, Graceta catal., Barcelona, 1890; Textura de las circunvoluciones ctrebrales de
las mameferos inferioreft, Gaceta sanitaria, Barcelona, 1890 ; Estructura fund, de la corteza cerebral de
los batracios reptiles y aves, Trabajos del laboratorio histologico, Barcelona, 1891 ; Sur la structure de
Vecorce cerebrals de quelyues mammiferes, La Cellule, torn, vii., 1891.

Conil, C. , Des resultats obtenus par la methode de Golgi appliquee d V etude du bulbe olfactif, Mem.
de la soc. de bidlogie, 1892.

Exner, Zur Kenntniss vom feineren Bau der Grosshirnrinde, Wiener Sitzungsb., Bd. 83, 1881.

Gehuchten, v., et Martin, Le bulbe olfactif chez quelques mammiferes, La Cellule, t. vii., 1892.

Golgi, Sulla fina struttura d. bulbi olfattori, 1875 ; Origine du tractus olfactorius et structure
des lobes olfactif s, Arch. ital. de biologic, t. i., 1882 ; Sulla, fina anatomia, degli organi centrali del
sistema nervoso, Rivista sperim. di freniatria, 1883.

202 RECENT LITERATURE OF THE BRATN.

Kb'lliker, v., Ue. d. feineren Ban des Bulbus olfactorius, Sitzungsb. d. Wiirzburg phys.-med.
Gesellschaft, 1892.

Lewis, Sevan, On the comparative structure of the cortex cerebri, Brain, vol. i., 1878.

Lewis, Bevan, and Clarke, On the cortical lamination of the motor area of the Brain, Proc.
Roy. Soc., 1878.

Major, H. C., Histology of the Island of Rei', West Riding Asylum med. Reports, vol. vi. ; and
Monthly Microsc. Journal, 1877.

Marchi, Sulla Jina anatomia, dei corpi striati, Rivista sperim. di freniatria, &c., 1883.

Martinotti, C., Beitrag z. Studium d. Hirnrinde u. d. Centralur sprung der Nervcn, Monthly
Int. Journ. of Anatomy and Physiology, vii., 1890.

Meynert, Th., Article "Brain," in Strieker's Histology, 1872.

Richet, C., Structure des circonvolutions cerebrales, Paris, 1878.

Sala, L., Zur feineren Anatomie des grossen Seepferdefusses, Zeitsch. f. wiss. Zool. , Bd. 52,
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Schaffer, K., Beitragzur Histologie der Ammonshornformation, Arch. f. mikr. Anat., xxxix., 1892.

Spitzka, E. C., Article " Brain, Histology," Ref. Handbook of the Medical Sciences, viii., 1889.

"Valpius, O., Ue. d. Entwickl. u. Ausbreitung der Tangentialfasern in der menschlichen Grcss-
hirnrinde, Arch. f. Psych., Bd. 23, 1892.

Weigrert, Bemerkungen u. d. Neurogliageriist, Anat. Anzeiger, 1890.

BBAIN-ME ASTJREMENT S.

Baistrocchi, Sul peso speciftco delTencefalo umano, &c., Rivist. sperim. di frenatr., 1884.

Bastian, H. C., Ue. d. specif, Gewicht verschiedener Theile d. menschl. Gchirns, Arch. f.
Heilkunde, 1866.

Bischoff, Th. L. W. v., Das Hirngewicht des Menschen, 1880.

le Bon, Of. , Recherches sur les Lois des variations du volume du cerveau, <fcc., Revue d'Anthropol.,
1879.

Braune, "Wilh., Das Gewichtsverhdltniss der rechten zur linken Hirnhdlfte beim Menschen, Archiv
fur Anat., 1891.

Buchstab, Beitr. z. Frage v. d. Gewichts- u. Grossenverhdltnissen des Gehirns, Abstr. in Neurol.
Centralbl. , 1885 (from a Russian dissertation, 1884).

Calori, Del cervello nei due tipi brachictphalo e dolicfiocephalo italiani, Bologna, 1875.

Clapham, C., On the weight of the brain in the insane, West Riding Asylum Medical Reports,
vols. iii. and vi. ; The brain-weights of some Chinese and Pelew Islanders, Journ. of the Anihropol.
Institute, 1878.

Conti, A., De I'dpaisseur de I'tcorce du cerveau humain, Internationale Monatsschrift fur Anatomie
u. Physiologic, vol. i., 1884.

Crichton-Browne, J., On the weight of the brain and its component parts in the insane, Brain,
vols. 1 and 2, 1879.

Danilewsky, B., Die quantitativen Bestimmungen der grauen und weissen Substanzen im Gehirn,
Centralblatt f. d. medicinischen Wissensch., 1880.

Davis, B., Contributions towards determining the weight of the brain in different races of man,
Phil. Trans., 1869.

Donaldson, H. H., Anatomical observations on the brain and sense organs of the blind deaf-
mute Laura Bridgman, Journal of Psychology, vols. 3 and 4, 1890 and 1891.

Huschke, E., Schadel, Him und Seele des Menschen und der Thieve nach Alter, Geschlecht und
Race, 1854.

Jensen, J., Untersuchungen uber die Beziehungen zwischen Grosshirn und Geistesstorung an scchs
Gehirnen geisteskranker Individuen, Archiv f. Psychiatric, vol. v. , 1875 ; Unters. u. 453 nach
MeynerVs methode getheilten u. gewogen Gehirnen, <£•<;., Ibid., xx. , 1889.

Krause, W., Ueber Gehirngewichte, Allgem. Wiener med. Zeit., 1888, and Internat. Monatschr. f.
Anat. u. Phys., V., 1888.

Major, H. C., A new method of determining the depth of gray matter of the cerebral convolutions,
West Riding Lunatic Asylum Med. Reports, 1872.

Manouvrier, De la quantite dans I'encephale, Mem. de la societe de 1'anthropologie, t. iii., 1888.

Marshall, J., Relations between the weight of the brain and its parts and the stature and mass of
the body in man, Journal of Anatomy and Physiology, July, 1892 ; The brain of the late George Grote,
with comments and observations on the human brain and its parts generally, Ibid., Oct., 1892.

Meynert, Th., Das Gesammfgcwicht u. die Theilgeivichte des Gehirnes, &c., Vierteljahrsschr. f.
Psych., 1867 ; Uc. d. Methode der Gehirnwdgungcn, Mittheil. d. Wiener anthropol. Gesellsch., Bd. 1,
1870.

Mercier, A., On the u-eight of the brain in the insane with reference to the hemispheres, lobes,
brain-stem and cerebellum, Journ. Mental Sc., vol. xxxvii., 1891.

Paulier, A. B., Recherches sur la notion de surface en anatomie. Determination de la surface du
cerveau, etc., 1892.

Snell, O., Die Abhdngigkeit des Hirngewichts von dem Korpergewicht und den geistigcn Fahig-
keiten, Archiv f. Psychiatric, Bd. xxiii., 1891 : Das Gewicht des Gehirnes, <&c., Miinchener medic.
Wochenschr., 1892.

Topinard, Le poids de I'encephale, Mem. de la societe de 1'anthropologie, t. iii., 1888.

Vierordt, H., Anatomixche, physiologixche und physikalische Datenund Tabellen, 1888.

RECENT LITERATURE OF THE BRAIN. 203

Wagner, H., Maassbestimmungen der Oberflache des grossen Gehirns, Inaug. Diss. , Gottingen, 1864.

Wagner, R., Vorstudien zu eincr v:isscnschaftiichen Morphologic und Physiologic dfs menschlichen
Gehirns ah Seelenorgan , 1860, 1862.

Weisbach, A., Die Gewichtsverhaltnisse d. Gehirns dsterreichischer Volker, Arch. f. Anthrop., I.,
1886.

MEMBRANES AND VESSELS OF THE BRAIN AND CORD.

Adamkiewicz, Albert, Die Blutgefasse des menschlichen Riickenmarkes ; I. Theil : Die Gefasse
der Riickenmarkes- Substanz, Sitzungsberichte der k. Akad. d. Wiss. in Wien, Bd. Ixxxiv., 3 AbtL.,
1881 ; //. Theil: Die Gefasse der Ruckenmarkes-Oberflache, Ibi.l., Bd. Ixxxv., 3 Abth., 1882 ; Die
Arterien des verldngerten Markes, Denkschr. d. Wiener Akademie, 1890.

Browning-, The veins of the brain and its envelopes, Brooklyn, 1884 ; Article " Vessels of the
Brain," Ref. Handbook of the Medical Sciences, viii., 1889 ; The arrangement of the supracerebral
veins in man, as bearing on HiWs theory of a developmental rotation of the brain, Journal of
Nervous and Mental Diseases, vol. 18, 1891.

Duret, H., Sur la, distribution des arteres nourricieres du bulbe rachidien, Archives de Physiologic,
1873 ; Rccherches anatomiques s. I. circulation de Vencephale, Ibid. 1874.

Hedon, E., Etude anatomique sur la circulation veineuse de I'encephale, These, 1888 ; abstract
in International Monthly Journal of Anatomy and Physiology, 1889.

Huebner, Zur Topographic der Erndhrungsgebiete d. einzelnen Hirnarterien, Centralbl. f. d.
raed. Wissen., 1872 ; Die luetische Erkrankung der Hirnarterien, Leipzig, 1874.

Kadyi, H., Ueber die Blutgefasse des menschlichen Riickenmarkes, 1889.

Key u. Retzius, Studien in der Anatomic des Nervensy stems, Stockholm, 1876.

Kolisko, Ue. d. Beziehung d. art. chor. ant. zum hinteren Schenkel der inneren Kapsel, Wien,
1891.

Labbe, C., Note sur la, circulation veineuse du cervcau, Archives de Physiologie, 1879 ; Etude, sur
les granulations de Pacchioni, <&c., These, Paris, 1882.

Mierzejewsky, J., Die Ventrikcl des Gehirns, Centralbl. f. d. med. Wissensch., 1872,

Ross, James, Distribution of the Arteries of the Spinal Cord, Brain, April, 1880.

Rossbach u. Lehrwald, Ueber die Lymphicege des Gehirns, Centralbl. f. d. med. Wissensch.,
1888.

See, M., Sur la communication des cavites ventriculaires de I'encephale avec les espaces sous-
arachnoidiens, Revue mensuelle, 1878 & 1879.

Sperino, GK, Circolazione venosa del capo, Torino, 1884.

Symington, J., On the valvular arrangements in connection with the cranial venous circulation,
Brit. Med. Journal. 1882.

Trolard, Recherches sur Vanatomie du systeme veineux de Vtnce'phale et du crane, These, 1868,
and in Archives generales de medecine, 1870 ; Les granulations de Pacchioni, Journ. de 1'anatomie et
de la physio!., t. 28 ; De quelques particularites de la dure-mere, Ibid., 1890.

Valenti, G., e Abundo, GK, Sutta vascularizazione ccrebralc, <kc., Atti d. soc. toscana di sci.
natur., vol. xi., 1890.

Windle, B. C. A., On the arteries forming the circle of Willis, Journ. of Anat. and Phys., xxi.,
1888.

ADDENDUM TO LITERATURE OP SPINAL CORD. (See pp. 34 to 37.)

Sherrington
Section I V. Relation
No. 6, 1892.

, C. S., Notes on the arrangement of some motor fibres in the lumbo sacral plexus,
ation of the limb to cell-groups in the spinal cord, Journal of Physiology, vol. xiii.,

INDEX AND GLOSSARY TO VOL. III. PART I.

ABDUCENT nerve. See NERVE, SIXTH.
Aberrant bundle of medullary striae, 50
Accessory auditory nucleus, 55, 60

cuneate nucleus. 53

flocculi, 76

nucleus, 20, 55

olivary nuclei, 57

Vttgal nucleus, 55

Acervulus cerebri (dim. of accrvus, heap), 114
Acoustic tubercle, 50

Affenspalte (German, ape-fissure), 143, 150, l$i
Age, influence of on brain-weight, 178, 180
Ala cinerea (grey wing), 50

lobuli centralis, 71, 73, 82
Algieri on tracts of Burdach, 32
Alveus (trough), 158, 172, 173
Amygdala cerebelli (amygdala, tonsil), 74, 76, 82
Amygdaloid nucleus, 124, 131, 135, 160, 169
Amygdalo-uvular lobe, 76
Angle, Rolandic, 143

Sylvian, 142
Angular gyrus, 151, 153
Annectent (connecting) gyri, 143, 144, 145, 146,

147, 148, 149, 150, 151, 152, 153, 156
Ansa (loop) lenticularis, 103, 112, 114, 135, 164

peduncularis, 112
Anterior column of cord, 9, 12, 22, 65

commissure of brain, 38, 98, 131, 135, 156,

160, 164
of cord, 6, 7, 10, 18

marginal bundle, 25

pillars or columns of fornix, 97, 113, 116,
129, 131, 158

pyramidal tract, 24, 31, 32, 45

roots of spinal nerves, 19, 32, 94
Antero-lateral ascending tract, 24, 25, 32, 34,
65, 85, 103, 104

descending tract, 24. 25, 32, 86, 93, 94

ground bundle, 26, 32

white columns, 9, 24, 31, 32, 64, 86, 95, 104
Apex cornu posterioris, 8
Aqueduct, nucleus of, 65

Sylvian, 96

central grey matter, 96, 98
epithelium of, 96

Arachnoid (opix^??, spider or spider's web) mem-
brane, i, 3, 137, 181, 187
Arachnoidal villi (villus, tuft of hair), 184, 190
Arbor vitse (from resemblance to shrub so

called) cerebelli, 71, 74, 76, 78
Arched or arcuate fibres, external or superficial,

44, 45, 58, 59
internal or deep, 53,

58, 93, 95. I04
Arcuate sulci of cerebellum, anterior, middle

and posterior, 75, 77
AreaofBroca, 159, 160
Areas of medulla oblongata, anterior, 43, 45
lateral, 43, 45
posterior, 41, 43

Arteries, cortical, 193
of dura mater, 184
lenticular, 197

lenticulo-optic (lenticulo-thalamic), 197
lenticulo-striate, 197
medullary, 193
of spinal cord, 191
Arterioles, central, 192
Artery of " cerebral haemorrhage," 197
Ascending auditory fibres, 63

cerebellar tract. See GEREBELLAR TRACT.
degeneration, 24, 27
frontal gyrus, 148, 163
parietal gyrus, 143, 148, 150, 151, 163
root of fifth nerve, 52, 63
tracts, 25, 26

Association-bundle, anterior, 165
inferior, 165
superior, 165
fibres, 158, 163, 165, 169

of cerebellum, 84
Auditory nerve. See NERVE.
nucleus, 104, 106

accessory, 55, 60
inner or dorsal, 56, 62
outer or superior, 56, 62
ventral, 56, 63
connections of, 103, 104, 106
Auerbach on degeneration in spinal cord, 34
Australians, brain- weight of, 180
Axis, cerebro-spinal, i

BAIF.LARGER on grey cortex, 177

lines of, outer and inner, 167
Band, furrowed, 76
Basal ganglia, 163, 172

optic ganglion, 116, 120
Basis pedunculi, 100
Basket cells, 89, 91
Bechterew on connections of upper olive, 60

fillet, 65

Beevor on cingulum, 158
fornix, 129
lyra, 131

Bellonci on optic lobes of birds, 107
Benedikt on brain of criminals, 161
Bergmann's fibres, 87
Bigeminal bodies, 106
Birds, cerebellum of, 69

optic lobes of, 107
Bischotf on brain- weight, 1 78
Biventral lobe of cerebellum, 74, 76, 82
Blood- vesssels of brain and cord, 191
Bochdalek on nerves of arachnoid, 189
Body of fornix, 129, 158
Body -weight, relation of brain-weight to, 178
Bordering gyrus, 159
Borders of cerebral hemisphere, 137
Boyd on brain- weight, 178

206

INDEX AND GLOSSARY TO VOLUME III. PART I.

Brachial enlargement of cord, 5

Brachium conjunctivum (connecting arm), 103

of quadrigeminal body, 105, no, in, j
117
Brachycephalic (&paxvs, short ; «€</>a\4 head) '

persons, brains of, 176, 177
Brain, i, 38. See also CERKBRUM, CEREBEL- i
LUM, PONS, and MEDULLA OBLONGATA.

blood-vessels of, 191, 193

commissures of, i, 38

dimensions of, 176

divisions of, 38

literature of, 199

lymphatics of, 198

measurements of, 176

membranes of, i, 181

ventricles of, 38, 47, 96, 97, 122, 188, 189

weight of, 1 78
Brain-sand, 114
Broca, area of, 159, 160

on brain-weight, 178

on grande lobe limbique, 155
Bulb. See MEDULLA OBLONGATA.

offornix, 115

olfactory, 145, 159, 174, 195

of posterior horn of lateral ventricle, 124
Bulbus rhachiticus (^X'J> backbone), 38
Bundle, olfactory, of cornu Ammonis, 1 58

posterior longitudinal, 58, 65, 66, 86, 93,

94, 95. 99. I02> I09, "4, "9
Burdach, tract of, 26, 28, 32, 44

CACUMINATE (cacumen, tip) lobe, 74, 77, 82
Cajal on collateral fibres, 21

on moss-fibres, 91

on optic lobes of birds, 107

on spongioblasts and neuroblasts, 14

on zone of superficial granules, 92
Calamus scriptorius (writing pen), 47
Calcar avis (bird's spur), 124, 144
Calcarine fissure, 124, 143, 144, 172

posterior, 144
Callosal fissure or sulcus, 127, 156

gyrus, 155, 156, 158, 160
Calloso-marginal fissure, 145, 146, 148
Calori on grey cortex, 1 77
Canal, central of cord, 9, 10, 19
Capsule, external, 134, 135, 164

internal, 100, 101, 104, in, 114, 119, 128,
131, 132, 133, 135, 136, 163, 166, 169,
172, 197

Caput cornu (head of horn), 8, 51, 52
Cat, ganglion cells of anterior nerve-roots of. 3

pyramidal tract of, 25
Cauda equiua (horse's tail), 3
Caudate (cauda, tail) nucleus, 124, 131, 134,

I3S» *36, 197

Causation of gyri and sulci, 162
Cavum (a hollow) Meckelii, 182
Cell-columns of cord, 14

of anterior horn, 14

Clarke's, 16, 34, 86

lateral, 16

middle, 17

of posterior horn, 17

posterior vesicular, 16
Cells, degeneration of, 24

ofDeiters, 13

outlying, 17

solitary, 17

Central arterioles, 192

canal of cord, 9, 10, 19

grey matter of mid-brain, 65, 96, 98

gyri, 143. HS, H9, 15°

ligament of cord, 2, 5

lobe of cerebral hemisphere, 133, 135, 145,

154, 177

cerebellum, 71, 73, 77
nucleus, oculomotor, 99
sulcus, 143

tract of tegmentum, 60
venules, 193

Centre, medullary, of cerebral hemisphere, 163
Centres, kinaesthetic, 163
psychomotor, 163, 172
for special senses, 163
visual, connection with cord and bulb, 119
inter-connection of, 119
connection with oculomotor nuclei,

119

Centrifugal arteries of cord, 192
Centripetal arteries of cord, 192
Cerebellar notch, anterior and posterior, 70

tract, antero-lateral descending, 24,

25, 32, 86, 93, 94
ascending bulbar, 86
direct, 24, 25, 32, 34, 44, 65,

85, 86
dorso-lateral ascending, 24, 25,

32, 34, 44, 65, 85, 86
ventro-lateral ascending, 24
25, 32, 34> 65, 85, 103, 104
Cerebellum (dim. of cerebrum, brain), 38, 69
arbor vitse of, 71, 73, 74, 76, 78
blood supply of, 195
commissures of, 84
connection with cortex cerebri, 86
fibres of crusta, 101
fourth nerve, 86
optic tract, 120
sixth nerve, 86, 93
third nerve, 86
cortex of, 87 '
crura of, 46, 84

degenerations following lesions of, 32, 93
divisions of, 69
fibres from posterior longitudinal bundle

to, 103

fissures of. See FISSURES.
hemispheres of, 69, 70, 78
laminae of, 71, 72, 86
literature of, 95
lobes of, 71, 74, 77
of lower animals, 69
nuclei in white mutter of, 83
peduncles of, 38, 46, 84

inferior, 69, 83, 86, 93, 95,

118
middle, 67, 70, 83, 85, 93, 94,

164

superior, 67, 69, 82, 83, 84,
93, 94, 100, 103, 164, 195
situation of, 69
size of, 7 1
sulci of, 71, 75, 78
surfaces of, 71,74
weight, of, 179, 180
white matter of, 71, 78, 87, 91
worm (vermiform process) of, 69, 71, 73, 74,

77, 78, 94

Cerebral hemispheres. See HEMISPHERES.
Cerebro-spinal fluid, i. 3, 188

INDEX AND GLOSSARY TO VOLUME III. PART I.

207

Cerebrum (brain), 38

comparison between male and female, 179

cortex of. See CORTEX.

crura of, 38, 96, 100, 118, 195

fissures of. See FISSURES.

peduncles of, 96, 100, 135

rotation of, 165

weight of, 179

See also HEMISPHERES.
Cervix cornu (neck of horn), 8, 52
Cervical enlargement of cord, 3, 5

nerves, effect of section of posterior roots, 28

nucleus, 16

region of cord, 10
Cetaceans, brain of, 162

Chiasma (x««C<«>, mark with letter X), olfactory,
1 60

optic, 96, 117, 198
Chinese, brain-weight of, 180
Choroid (correctly chorioid, from \6pwv, mem-
brane) plexuses of fourth ventricle, 50,
185, 186, 195

of lateral ventricles, 122, 124, 155, 185, 198

of third ventricle, 98, 185, 198

vein, 185
Choroidal fissure, 126, 155

villi, 1 86

Ciliary muscle, origin of nerve-fibres to, 99
Cingulum (girdle), 129, 158, 165
Cisterna (reservoir) cerebello-medullaris, 188

chiasmatis, 188

corporis callosi, 188

fossae Sylvii, 188

interpeduncularis, 188

laminae cinerese, 188

peripeduncularis, 188

pontis lateralis, 188

media s. basilaris, 188
Cisteruse arachnoidales, 188
Clarke's column, 16, 53, 86

effects of destruction cells

in, 34

Claustrum (rampart), 134, 135. 169
Clava (club), 143
Clendinning on brain- weight, 178
Clivus (slope), 70, 73, 79
lobe of, 74, 77
monticuli, 71

Cochlear root of auditory nerve, 63
Collateral eminence, 127, 145

fibres of, 21, 65, 88, 163, 164
fissure, 127, 144, 153
Columnae fomicis, 129
Columns, white, of cord, 8, 14, 22

anterior, 9, 12, 22, 65
antero-lateral, 9, 24, 31, 32,

64, 86, 95, 104
lateral, 9. 12, 64
of Lissauer, 20, 26, 29
posterior, 9, 26, 27, 29, 32, 53,

63

postero-lateral, 7, 28, 44
postero-mesial, 7, 10, 28, 43
fornix, anterior, 97, 113, lib, 129

posterior, 124, 129, 130
medulla oblongata, 40, 41, 104
Comet cells, 17
Comma tract, 26, 29, 32
Commissnra (uniting band) baseos alba, 128
Commissural fibres of cerebellum, 84

of cerebrum, 163, 164, 169, 1 72
between hippocampi, 131

Commissures; i

anterior, 98, 135
of cerebellum, 84
of cerebrum, anterior, 38, 98, 131, 135, 156,

i 60, 164

middle, 38, 96, 97, in, 113
posterior, 38, 98, 104, 109,

114, 117. 119
of cord, i, 6, 7, 10, 18, 34
great, 127

inferior, of Gudden, 117, 118
of Meynert, 120

middle or soft, 38, 96, 97, in, 113
optic, 117

posterior, 98, 104, 109, 114, 119
Conarium (K&VOS, pine-cone), 1 14
Conducting tracts of cord, 22
Cone, fibrous, 163
Conns medullaris, 5
Convoluted brains, 162
Convolutions. See GTRI.
Cord. See SPINAL CORD.

Cornu Ammonis (from its resemblance to the
horns on the statue of Zeus-Ammon), 124,
158, 169, 172
Cornua of grey matter of cord, 8, 10, 32, 51, 52,

53, 58, 104
cell-columns of, 14
Cornucopia (horn of plenty), 50
Corona radiata, 107, 109, 119, 135, 136, 163
Corpora albicantia (white bodies), s. inamillaria
(mamilla, nipple), 96, 98, III, 113, 115,

129, 1 66, 198

amylacea (&fj.v\ov, starch), 14
bigemina (two), 38, 106

geniculata (genii, knee), 105, 109, in, 117,

118, 119, 195
quadrigemina (four), 38, 96, 104, 109, no,

117, 119, 164, 195
Corpus callosum (callosus, hard), 38, 122, 127,

130, 137, IS6, !64, 166, 197
absence of, 162

peduncles of, 128, 155, 158, 159
Corpus trapezoides, 73, 78, 79, 82
Cortex (bark) cerebelli. 87
cerebri, 163

cells of, 167

connection with cerebellum, 86
crusta, 101, 136
hippocampal and
callosal gyri, 158
internal capsule, 136
lower olives, 86
upper fillet, 104
degenerations after lesions of, 31 . 86,

164

occipital region of, no, 136
prefrontal region of, 136, 163
Rolandic region of, 136
visual area of, 1 10
Cortical arteries, 193
Course of fibres in cord, 22

of cord through medulla oblon-
gata and pons, 63
Cranial nerves, 93, 95

Crescentic lobes of cerebellum, 71, 73, 74, 82
Criminals, frontal lobe of, 161
Crossed pyramidal tract, 24. 31, 32, 51, 64

root of fifth nerve, 62
Crura (crus, leg) ad cerebrum, 84
medullam, 86
poutem, 85

208

INDEX AND GLOSSARY TO VOLUME III. PART I.

Crura — continued.

cerebri, 38, 96, 100, 118, 195
fornicis, 129, 130
Crural enlargement of cord, 5
Crnsta (rind) connection with cortex, 101, 136
mesial bundle of, 67
pedunculi, 100, in, 114, 115, 132, 136,

163, 164

Culmen (summit) monticuli, 70, 71, 73, 79
Cuneate funiculus, 44

lateral, 44
lobule, 152, 197
tubercle, 44

Cuneo-limbic annectent gyrus, 144
Cuueo-lingual annectent gyrus, 144
Cuneo-quadrate annectent gyrus, 144
Cuneus (wedge), 143, 152, 153, 156
Cunningham on cerebral convolutions, 162
inferior frontal sulcus, 148
intraparietal sulcus, 150
Rolandic angle, 143

DANILEWSKY on grey cortex, 177
Darkschewitsch on Gudden's commissure, 118
optic tract, 117
posterior commissure, 109
Decussating commissural fibres of cerebellum, 84
Decussation of fillet, 53

pyramids, 46
Degeneration of nerve-cells, 24

nerve-tracts in spinal cord,
ascending, 24, 27
descending, 24, 27
secondary, 24
tertiary, 24
in spinal cord from lesions in cerebellum,

32, 93

in cerebrum, 31
long, 32
short, 32
Deiters, cells of, 13

on formatio reticularis, 58
nucleus of, 56, 62
Dentate fissure, 156, 158

gyrus, 127, 155, 156, 158, 172
De Regibus on grey cortex, 177
Descending cerebellar tract, antero-lateral, 24,

25, 32, 86, 93, 94
degeneration, 24, 27
horn oflateral ventricle, 122, 124, 130
root of fifth nerve, 65, 100
tracts, 24, 26, 94
Dimensions of brain, 176
Direct cerebellar tract, 24, 25, 32, 34, 44, 65, 85, 86

lateral, 25

pyramidal tract, 24, 31, 32, 45
sensory tract, 163
Dolichocephalic (8oA«x<5s, long ; K«t>a\-fi, head),

persons, brains of, 176, 177
Donaldson on grey cortex, 177
Dorsal cell-group of anterior horn, 14

column of medulla oblongata, 40
longitudinal bundle, 58, 65, 66, 86, 93,

94, 99, 102, 109, 114, 119
nucleus, 16
oculomotor nuclei, 99
olfactory root, 160
part of mid-brain, 104
region of cord, 10
Dorso-lateral ascending cerebellar tract, 24, 25,

32, 34, 44, 65, 85, 86
cell-group of anterior horn, 14
4 'i.

Dura mater (dura, hard ; mater, in the sense of
that which produces or nourishes : trans-
lated from the Arabic), i, 3, 181
anterior ligament of, 182
Duret on arteries of brain, 197, 198

cisternae arachnoidales, 188
Duval on connection between third and sixth
nerves, 63, 99

EDINGER on fillet, 65, 103, 104
and Westphal, nucleus of, 99

Eighth nerve. See NERVE, AUDITORY.

Elasmobranch fishes, pineal body of, 45, 115

Eleventh nerve. See NERVE, SPINAL ACCES-
SORY.

Eminentia cinerea (grey eminence), 50
collateralis, 127, 145
teres (rounded, cylindrical), 51

Encephalon (eV, in ; /ce^aA.ij, head). See BRAIN.

Enlargements of cord, 3, 5

Ependyma (^Si^ua, clothing), 62, 98, no, 132

Ependymal fibres, 96

Epidural (tiri, upon ; dura mater) space, 182

Epiphysis (tirityvw, grow upon) cerebri, 114

Ergot (French, spur), 124

Exposed surface of cortex, 137, 177

Extent of grey cortex, 1 76

External capsule, 134, 135, 164

geuiculate body, 105, 109, in 117,

"9, 195

perpendicular fissure, 144
Extraciliar fibres, 85

Extra ventricular portion of corpus striatuin, 132
Eyes, effects of extirpation, no, 118, 119

FACIAL nerve. See NERVE.

nucleus. See NUCLEUS.
Falciform lobe, 155
Falx (falx, sickle) cerebelli, 182, 183

cerebri, 137, 182

minor, 183
Fascia dentata (toothed bundle) Taiini, 156, 172,

174
Fasciculus (small bundle) arcuatus, 165

longitudinal, inferior, 165
superior, 165

perpendicular, 165

retroflexus, 113

(or funiculus) teres, 50, 53, 63

uncinate, 165

Fasciola (small bandage) cinerea, 157, 158
Fibres, collateral, 21, 65, 88, 163, 164

ependymal, 96
Fibrse propriae, 165

rectse, 59
Fibrous cone, 163
Fifth nerve. See NERVE.

nuclei of. See NUCLEUS.
Fillet, 53, 65, 66, 93, 109, 164

decussation of, 53

lateral or lower, 66, 103, 105

mesial, 67, 101, 103

tract of, 103

upper, 104, 107, 114, 119, 120

upper nucleus of, 104
Filum (thread) terminale, 2, 5, 189
Fimbria (fringe), 124, 130, 157, 158, 159, 166,

172

Fimbrio-dentate sulcus, 157
First nerve. See NERVE, OLFACTORY.
Fishes, pituitary body of, 116

segmentation of spinal cord in, 16

INDEX AND GLOSSARY TO VOLUME III. PART I.

209

Fissura choroidea, 155
prima, 159
serotina (late), 159

FISSUKES (see SULCI) of cerebellum, 71, 75,78, 79
antero-superior, 71, 73
great horizontal, 71, 75, 79, 82
intraculrninate, 82
intralobular, 72
midventral, 77
postclival, 71, 73, 79, 82
postero-superior, 71, 73
postnodular, 75, 79
postpyramidal. 75, 79
preclival, 71, 73, 79, 82
prepyramidal, 75, 79
of cerebrum, 137

calcarine, 124, 143, 144, 172

posterior, 144
callosal, 127, 156
calloso-marginal, 145, 146, 148
choroidal, 126, 155
collateral, 127, 144, 153
dentate, 156, 158
external perpendicular, 144
great longitudinal, 129, 137
hippocampal, 124, 156, 158
interior, 124
liinbic, 155, 160
paracentral, 145
parallel, 153

parieto-occipital, 124, 143, 144
paroccipital, 150
prelimbic, 145

of Rolando, 143, 150, 154, 155
of Sylvius, 141, 143, 146, 147,

148, 150
transverse, 124
variations in, 161
See also SULCI.
of medulla oblongata, 40
or furrows of spinal cord, 6, 7
Flechsig on fillet, 65
Flocculus (dim. offloccus, flock of wool), 74, 75,

82

accessory, 76
Fluid, cerebro-spinal, i, 3, 188

subarachnoid, 187
Flumina (rivers), 188
Folia (folium, leaf) of cerebellum, causation of,

162

Folium cacuminis (of the tip), 71, 74, 79
Foramen csecum, 40

of Majendie, 48, 188
of Monro, 97, 122, 129
Forceps (pincers) major, 124, 129, 166

minor, 128

Forel on Meynert's bundle, 1 14
tegmentum, 114
tract of fillet, 103
pillars of fornix, 129
Formatio reticularis, 51, 52, 58, 60, 65, 100, 101,

102, 103, 114, 164
alba (white), 58, 65
grisea (grey), 58

Formation of cornn Ammoni.s, 169
Fornix (arch or vault), 122, 128, 129, 155, 158,

159, 1 66
bulbs of, 115

pillars or columns of, anterior, 97, 113, 116,
129, 131, 158
posterior, 124, 129,
13°, 157, 158

Fossa rhomboidalis, 47
Sylvian, 142
Tarini, 115
Fourth nerve. See NERVE.

nucleus of. See NUCLEUS.
ventricle, 47, 73

floor of, 50

Fovea (pit) inferior, 50
superior, 50

Foville on tsenia semicircularis, 131
Frsenulum (frenum, bridle) veli, 104
Frsenum lingulse, 73
Freud on solitary cells of lamprey, 17
Frontal convolution. See GYRUS.

lobe, 112, 145, 156, 160, 161, 164, 165, 177,

180, 195
operculum, 142
pole of hemisphere, 137, 147
sulci. See SULCI.
Fronto-limbic annectent gyrus, 149
Fronto-marginal sulcus, 146

lateral, 146, 149
Fronto-parietal operculum, 142
Fuchs, brain of, 176
Funiculus cuueatus (wedge-shaped cord), 44

lateralis, 44
gracilis (slender), 43
of Rolando, 44, 52
solitarius, 55
(or fasciculus) teres, 50, 53> 63

nucleus of, 54, 65
Furrowed band, 76
Fusiform lobule, 153, 166

GALEN, veins of, 185
Gambetta, brain of, 161

Ganglia or ganglion (yd.yy\ioi>, swelling), basal,
163, 172

basal optic, 116, 120

ofhabenula, 103, 113, 117

of hemispheres, 131

interpedunculare, 103, 114

optic, 109

radicis cochlearis, 55

of roof, 108

of spinal nerve-roots, 3
Ganser on quadrigeminal bodies, 107
Gauss, brain of, 176
Gehuchten on collateral fibres, 21
olfactory bulb, 176
Geniculate body, external, 105, 109, ill, 117,

"9, 195

internal, 105, 109, 118, 195
Genu (knee) of corpus callosum, 128
of fissure of Rolando, 143
of internal capsule, 136
Giacomini on brains of criminals, 161
gyrus Rolandicus, 143
dentatus, 157
longus insulse, 155
Gland, pineal, 96, 97, 104, 114
Glandulse Pacchionii, 190
Globus pallidus (pale sphere), 134, 164
Glomeruli (dim. of glomus, clue of thread),

olfactory, 175, 176
Glosso-pharyngeal nerve, origin of, 40, 54, 55

nucleus, 55

Golgi on classification of nerve-cells, 17
collateral fibres, 22
fascia dentata, 173
olfactory bulb, 176

210

INDEX AND GLOSSARY TO VOLUME III. PART I.

Goll, tract of, 26, 28, 32, 34, 43

Graaf, de, on pineal body, 115

Gracile nucleus, 53, 86

Grande lobe limbique, 155

Granule-layer of cerebellar cortex, 87, 89, 90

of olfactory bulb, 174
Great commissure of cerebrum, 127

horizontal fissure of cerebellum, 71, 75, 79, 82
longitudinal fissure, 129, 137
Grey commissure of cord, 7
matter, central, 65, 98

of aqueduct, 96, 98
of cord, 7, 13

connection with visual centres, 119
effect of destruction, 34
ganglionic or cell-columns of, 14
horns or cornua of, 8
intermediate grey substance of, 8
intermedio-lateral tract of, 8
microscopic structure of, 13
processus reticularis of, 8
proportion of, to white matter, 7, 10
of hemispheres, structure of, 166
of medulla oblongata, connection with

visual centres, 119
olfactory root, 159, 160
Grooves or sulci of medulla oblongata, 40, 41
Ground-bundle, antero-lateral, 26, 32
Gudden, commissure of, 117, 118

on connection between cerebellum and olive,

57

optic fibres, 118
pillars of fornix, 129
Guinea-pig, optic chiasma of, 118

pyramidal tract of, 25
GYRUS or GYRI (yvpos, ring), 137
angular, 151, 153
annectent, 143, 144, 145, 146, 147, 148, 150,

151. 152, J53» 156
bordering, 159
breves insula?, 155
brevis accessorius insulse, 155
callosal, 155, 156, 158, 160
causation of, 162
central, 143, 148, 149, 150
of central lobe, 154
cinguli, 156

cuneo-limbic annectent, 144
cuneo-lingual annectent, 144
cuneo-quadrate annectent, 144
dentatus, 127, 155, 156, 158, 172
fornicatus, 156, 158, 165
effect of removal, 32
fornicis, 155, 158
frontal, 143, 146, 147, 148, 150, 154, 161,

163, 165, 172, 195
fronto-limbic annectent, 149
geniculi, 155. 158
hippocampal, 153, 155, 156, 158, 159, 160,

161, 164, 165, 167
infracalcarine, 153
infracallosus, 155, 158, 159
limbicus, 158
lingual, 156
longus insulae, 155
marginal, 145, 146, 148, 150. 159
occipital, 152

occipito-temporal annectent, 152
orbital, 149

parietal, 143, 148, 149, 150, 151, 163
parieto-occipital annectent, 151, 152
postcentral, 150

GYRUS or GYRI — continued.
postparietal, 151, 152, 153
precentral, 147, 148
rectus, 149
Rolandicus, 143
subcalcarine, 153
subcallosus, 155, 158, 159
supracallosal, 155, 158 -
supramarginal, 151, 1 53
temporal, 151, 152, 153, 155
transverse temporal, 153
transversus insulse, 154
nncinate, 156, 172
variations in, 161

HABENULA (dim. of habena, thong or rein), in

ganglion of, 103, 113, 117
Hemiextirpation of cerebellum, 93
Hemisection of spinal cord, 33, 104
Hemispheres of cerebellum, 69, 70, 78

connection with cerebral cortex, 86
of cerebrum, 38, 122, 137
blood-supply of, 195
commissures of. See COMMISSURES.
dimensions of, 176
fissures of. See FISSURES.
ganglia of, 131

grey matter, structure of, 166
intimate structure of, 163
lobes of, 137, 145
mantle of, 135, 142, 154
stem of, 154
ventricles of, 122
weight of, 178

white matter, structure of, 163
Hensen on oculomotor nucleus, 99
Heubner on arteries of brain, 198
Hill on rotation of cerebrum, 165
Hindus, brain-weight of, 180
Hippocampal fissure, 124, 156, 158

gyrus, 153, 155, 156, 158, 159, 160, 161,

164, 165, 167

Hippocampus (from fancied resemblance to limb
of fabulous animal thus named) major,
124, 130, 131, 158, 172
minor, 124
His on funiculus solitarius, 55

origin of neuroglia- and nerve-cells, 14
Hoche on ganglion-cells in anterior nerve-roots, 3
Horizontal fissure, great, of cerebellum, 71, 75,

79, 82

sulcus, lower or lesser, 75, 77
Horns of grey matter of cord. See CORNU.

lateral ventricle, 122, 124, 130
Horse, olfactory lobe of, 159
H-shaped sulcus, 149
Huschke on brain-weight, 180
Hypoglossal nerve. See NERVE.
Hypophysis (virS, under ; <f>vca, grow) cerebri. 97,
116

INCISURA marsupialis (pouch-shaped notch), 70

semilunaris, 70
Index, occipital, 151
Inferior fissure of cerebrum, 124
Infracalcarine gyrus, 153
Infundibulum (tunnel), 96, 97, 98, 116, 198
I nnervation of orbital muscles, 99, 119
Intellectual development, influence of, on dimen-
sions of brain, 176

on fissures and convolutions, 161
Inter-brain, 96

INDEX AND GLOSSARY TO VOLUME III. PART I.

211

Intercentral connections of visual apparatus, 1 19
Interlobular fissures of cerebrum, 137
Intermediate grey substance of cord, 8

process, 8

sulcus, anterior, 24

posterior, 7

Intermedio-lateral tract, 8
Internal capsule, 100, 101, 104, in, 114, 119,
128, 131, 132, 133, 135, 136, 163, 166,
169, 172, 197

medullary lamina, 112, 114, 134
Interolivary layer, 63
Intel-peduncular ganglion, 103, 1 14
Intraciliar fibres, 85
Intraculminate fissures, 82
Intralobular fissures of cerebellum, 72
Intraparietal sulcus, 149, 155
Intra ventricular portion of corpus striatum, 131
Involuted medullary lamina, 174
Island of Reil, 133, 141, 145, 154, 164
Isthmi lobi centralis, 135
Isthmus of brain, 38

of gyrus fornicatus, 156
Iter a tertio ad quartum ventriculum, 96

JELGERSMA'S theory of causation of cerebral
gyri, 162

KEY on cisternse arachnoidales, 188

septum posticum of cord, 188
Kinaesthetic (nivTiais, motion ; &tff6ri(ris, percep-
tion) centres, 163
Kolliker on collateral fibres, 21

nerves of arachnoid, 189
Krau.se, W., white plexuses of, 169

LABORDE on connection between third and sixth

nerves, 63, 99

Lacunae laterales (lateral hollows), 184, 191
Lamina (layer), anterior and posterior perfo-
rated. &ee PERFORATED SPACE.
Laminae arcuatse gyrorum, 165

cinerea (grey), 96, 98, 117

cornea, 122

medullary, inner, 112, 114, 134
involuted, 174
outer, in, 114, 134

quadrigemina, 96

septi lucidi, 155, 159

of cerebellum, 71, 72, 86

trausversales inferiores, 77
Lamprey, solitary cells of, 17
Lancisi, nerves of, 127
Lateral area of medulla oblongata, 43, 45

cell-column of cord, 16

cell-group of anterior horn, 14

column of cord, 9, 12, 64

medulla oblongata, 40

cuneate funiculus, 44

fillet, 66, 103, 105

horn of grey matter, 8, 10, 32, 52
lateral ventricle, 122, 124

nucleus. See NUCLEUS.

pyramidal tract, 24, 31, 32, 51, 64

recess, 47, 48, 49, 188

sinus, 182, 184

sulcus, 100

ventricle, 97, 122
Latin races, brain-weight of, 180
Latticed layer of thalamus, 112

Lemniscus (ribbon), 53

Lenhossek on basal optic ganglion, 1 16

Lenticular arteries, 197

nucleus, 101, 112, 114, 120, 132, 136, 164,

197
Lenticulo- optic (lenticulo-thalamic) arteries,

197

Lenticulo-striate arteries, 197
Leptomeninx (Kern-fa, thin ; juV'Tl, membrane),

181
Lesions of cerebellum, effects of, 32, 93

cortex cerebri, effects of, 31, 86, 164

optic thalamus, effects of, 85

spinal cord, effects of, 32
Lesser horizontal sulcus. 75, 77
Ligament, anterior, of dura mater, 182

central, of cord, 2, 5
Ligamentum denticuliitnm (denticulus, dim. of

dens, tooth), 3, 188, 189
Ligula (dim. of lingua, tongue), 49, 50
Limbic (limbus, surrounding border) lobe, 145,
149, 154, 155, 159, 160, 161, 165, 166

fissure, 155, 1 60

Limen insulae (threshold of island), 155
Line of Baillarger, inner and outer, 167

Vicq d'Azyr, 167
Linea splendens (brilliant), 186
Lingual gyrus, 156

lobule, 153

Lingula (dim. of linfftia, tongue), 48, 71, 73, 82
Lissauer's column or tract, 20, 26, 29
Literature of brain, 199

cerebellum, 95

medulla oblougata and pons, 67

mid-brain, 120

spinal cord, 34

Lizard, posterior longitudinal bundle of, 102
LOBE or LOBES, amygdalo-uvular, 76

biventral, 74, 76, 82

central, of hemispheres, 133, 135, 145, 154,

177
of vermiform process, 71, 73, 77

of cerebellum, 71, 74, 77

of clivus, 74, 77

cresceutic of cerebellum, 71, 73, 74, 82

falciform, 155

frontal, 112, 145, 156, 160, 161, 164, 165,
177, 180, 195

of cerebral hemispheres, 137, 145

inferior seinilunar, 74, 77, 82

limbic, 145, 149, 154, 155, 159, 160, 161,
165, 166

occipital, 112, 119, 145, 151, 153, 163, 164,
165, 166, 177, 180, 195

olfactory, 145, 158, 159, 164, 174

optic, 38

of birds, 107

parietal, 112, 145, 149, 153, 177, 180, 195

of pituitary body, 116

postero-superior of cerebellum, 71, 74, 82

posterior of cerebellum, 74

of pyramid, 77

quadrilateral of cerebellum, 74

slender, 74, 77

temporal, 112, 145, 149, 152, 156, 160,
163, 164, 165, 177, 180, 195

temporo-sphenoidal, 152

of under surface of cerebellum, 75

of upper surface of cerebellum, 73

of vermiform process, 77
Lobule, cuneate, 152. 197

fusiform, 153, 166

p 2

212

INDEX AND GLOSSARY TO VOLUME III. PART I.

Lobule, lingual, 153

olfactory, anterior, 159, 160
posterior, 159

oval, 149

paracentral, 149, 150

parietal, inferior and superior, 150, 151,
152, 1 66

postccntral, 154, 155, 156

precentral, 154, 155

quadrate, 149, 151, 156
Lobulus gracilis, anterior and posterior, 75
Lobus eacuminis, 74, 77, 82

cen tralis, 77

clivi, 73, 74, 77

cuhninis, 73, 77

gracilis (slender), 77, 82

hippocampi, 161

int'undibuli, 116

lingulte, 77

lunatus (crescent-shaped) anterior, 73
posterior, 74

noduli, 75, 76, 77

pyramidis, 76, 77

tuberis, 75, 77

uvulae, 76, 77
Locus cceruleus (dark-blue place), 51, 98

perforatus posticus, 115
Long association fibres, 165

degenerations, 32

Longitudinal bundle, posterior or dorsal, 58, 65,
66, 86, 93, 94, 99, 102, 109, 114, 119

fissure, great, 129, 137

sinus, inferior, 182

superior, 152, 182, 184, 191
Longitudinal striae, lateral or grey, 127, 155,

157, 158

mesial, 127, 128, 155, 157,158
sulcus of midbrain, 104
Lower stalk of thalamus, 112
Lumbar enlargement of cord, 3, 5

region of cord, 10
Luschka on arachnoid al villi, 191

on nerves of arachnoid, 189
Luys, nucleus of, 114, 120

on outer olfactory root, 160
Lymphatics of brain and cord, 198
pituitary body, 116
Lymph-spaces of dura mater, 184

nerve-sheaths, 189
pia-mater, 186
Lyra (lyre), 130

MAJKNDIE, foramen of, 48, 188
Malays, brain-weight of, 180
Mantle, 135, 142, 154
Marchi on lesions of cerebellum, 32, 93

tract of Burdacli, 32
Marginal bundle of nerve-libres, 8, 25

gyrus, 145, 147, 148, 150, 159

effects of lesion, 31
Marrow, spinal, 2
Marshall on brain -weight, 180
Measurements of brain, 176
Medulla oblongata (medulla, marrow ; oblongrus,
.greater in length than breadth, oblong),
areas of, 41, 43, 45

blood-supply of, 194

columns of, 40, 41, 104

external characters of, 38

fissures of, 40

form of, 39

grooves or sulci of, 40, 41

Medulla oblongata — continued.
internal structure of, 51, 53
literature of, 67
measurements of, 39, 179
origin of nerve-roots from, 40
situation of, 38
structure of, 40, 51
Medulla spinalis (spinal marrow), 2
Medullary arteries, 193

centre of cerebral hemispheres, 163
lamina, external, in, 114, 134
internal, 112, 114, 134
involuted, 174
striae, 50, 59, 94

aberrant bundle of, 50
velum, inferior, 48, 70, 76, 78

superior, 47, 70, 79, 82, 85, 98,

103, 104

Membranes of brain and cord, I, 3, 181
Mendel on origin of facial nerve, 61

superior cerebellar peduncle, 85
Meninges (jU^i/ry£, membrane), 181
Merkel on cleft in descending cornu, 126, 188
Mesencephalon (jueVos, middle ; fjKf^>a.\ov, brain),

96

Mesial bundle of crusta, 67, 115, 164
cell-group of anterior horn, 14
fillet, 67, 101, 103

longitudinal striae, 127, 128, 155, 157, 158
Meynert on brain-weight, 180
bundle of, 103, 113
commissure of, 120
on claustrum, 135

cortical cell-layers, 167
nucleus fastigii, 84
olfactory chiasma, 160
posterior commissure, 109
stratum dorsale, 114

intermedium, 101
Microscopic structure of cord, 12

cerebellar laminae, 86
cerebral cortex, 166
Midbrain, 38, 96

dorsal part of, 104
literature of, 120
transition from pons to, 65
Middle cell-column, 17

cerebellar peduncle, 38, 46, 67, 70, 83, 85,

93, 94, 164

horn of lateral ventricle, 122, 124
or soft commissure, 38, 96, 97, in, 113
Midfrontal sulcus, 146, 147
Midgracile sulcus, 75
Midventr.tl fissure, 77
Mitral cells, 174, 176
Mole, posterior longitudinal bundle of, 103

quadrigeminal bodies of, 105, no
Molecular layer of cerebellar cortex, 87
cerebral cortex, 167
Monakow on anterior brachium, 107
Monkey, fornix of, 129
parallel fissure of, 153
pyramidal tract of, 25, 31
Sylvian fissure of, 142

See also QUADRUMANA.
Monro, foramen of, 97, 122, 129
Monticulus (dim. of mons, mountain) of cere-
bellum, 71
Moss-fibres, 91
Motor cell-column, 14

nucleus of fifth nerve, 61
region, effects of removal, 31

INDEX AND GLOSSARY TO VOLUME III. PART I.

213

Mott on cells of Clarke's column, 16

section of nerve-roots, 2"j
Mouse, optic chiasma of, 118

pyramidal tract of, 25, 31
Munzer on degeneration in spinal cord, 34

on tract of Burdach, 32
Muscles, orbital, innervation of, 99, 119
Myelin-sheath, development of, in cord, 22

NATES, 105

Negro, brain- weight of, 180

first frontal gyrus of, 147
NERVE or NERVES (vevpov, nerve), abducent.

See NERVE, SIXTH.
of arachnoid membrane, 188
auditory, 95, 106

ascending root of, 56
cochlear root of, 63
connection with inferior quadrige-
minal body, 106
restiforinbody, 86
nuclei, see NUCLEUS
origin of, 55
cranial, 93, 95
of dura mater, 184
eighth. See NERVE, AUDITORY.
eleventh. See NERVE, SPINAL ACCESSORY.
facial origin of, 40, 55, 61, 63

degeneration in, after cerebellar le-
sions, 93
fifth, central tract of, 62

degeneration in, alter cerebellar lesions,

93
origin of, 40, 51, 61, 65, 98

trophic fibres of, 51
roots of, ascending, 52, 63, 93

degeneration after section, 53
crossed, 62
descending, 65, loo
raphe, 62

first. See NERVE, OLFACTORY.
fourth, 98, 102, 103

connection with cerebellum, 86

sixth, 66

glosso-pharyngeai, 40, 54, 55
hypoglossal, 93, 95

origin of, 41, 53, 57
of Lancisi, 127

ninth. See NERVE, GLOSSO-PHARYNGEAL.
oculomotor. See NERVE, THIRD.
olfactory, 159, 175,
origin of, from medulla oblongata, 40

spinal cord, 3, 19
optic, 93, 118

connection with anterior quadri-

geminal bodies, 105
phrenic, 16
of pia mater, 187

pneumo-gastric. See NERVE, VAGUS.
second. See NERVE, OPTIC.
seventh. See NERVE, FACIAL.
sixth, connection with cerebellum, 86, 93
fourth, 66
third, 63, 66, 99
origin of, 42

spinal accessory, 16, 20, 40
tenth. See NERVE, VAGUS.
third, 93, 95, 98, 99, 102, 103

connection with cerebellum, 86

sixth, 63, 66, 99
roots of, loo
trigeminal. See NERVE, FIFTH.

Nerve or nerves — continued.

trochlear. See NERVE, FOURTH.
twelfth. See NERVE, HYPOGLOSSAL.
vagus, 40, 54, 55
Nerve-cells of cerebellum, 87
of cord, 10, 13, 14, 34
of cortex cerebri, 167
degeneration of, 24
of medulla oblongata, 53, 56, 58
of optic lobes, 108

Nerve-fibres of cerebral hemispheres, 163
of cord, course of, 22

degeneration of, 24, 27
size of, 12

traced through bulb and pons, 63
Nerve-roots, spinal, 3, n, 20, 94
anterior, 19, 32, 43, 93
ganglia of, 3
posterior, 20, 29

collateral fibres of, 21
degeneration following section of, 27
relation to spines of vertebrae, 3

See also NERVE.
Neurilernina (vtvpov, nerve ; Ae/t^a, peel or skin)

of cord, 1 86
Neuroglia (vevpov ; y\ia, glue), 12, 62, 87, 92,

96, 98, 106, 159, 167, 174
Nidus avis (bird's nest), 76
Ninth nerve. See NERVE, GLOSSO-PHARYNGEAL
Nodule, 74, 75

North American Indians, brain-weight of, 180
Notch, cerebellar, anterior, 70

posterior, 70

NUCLEUS (kernel) or NUCLEI, ambiguus, 55
amygdalae, 124, 131, 135, 160, 169
of aqueduct, 65
auditory, 104, 106
accessory, 55, 60
inner or dorsal, 56, 62
outer or superior, 56
ventral, 56, 63
caudatus (tailed), 124, 131, 134, 135, 136,

197

centralis, 58
cervical, of cord, 16
of corpus albicans, 115
of Deiters, 56, 62
dentatus, 82, 83, 84, 85
dorsal, of cord, 16
of Edinger and Westphal, 99
emboliformis, 83
facial, 6 1

connection with oculomotor, 103
fastigii (roof), 83, 84
of fifth nerve, motor, 61

sensory, lower, 62
upper, 6 1

of fourth nerve, 98, 102
of funiculus cuueatus, 53, 86
external or accessory, 53
of fuuiculus gracilis, 53, 86

teres, 54, 65
globosus (spherical), 83
glosso-pharyngeai, 55
hypoglossal, 53
lateral, of cord, 1 7

of medulla oblongata, 52
of thalarnus, 112
lateralis, 52
lenticular, 101, 112, 114, 120, 132, 136,

164, 197
of Luys, 114, 120

214

INDEX AND GLOSSARY TO VOLUME TIL PART I.

NUCLEUS or NUCLEI — continued.

oculomotor, 98, 102, 109, 114, 117, 118

central, 99

connection with, facial, 103

dorsal, 99

ventral, 99
olivary, 56

accessory, 57

connections of, 56, 86

superior, 47, 60

of optic thalamus, 112, 113, 114, 129
pontis, 60, 86, 93, 101
pyramidal, 57

of quadrigeminal bodies, 105
red, 103, 114
of roof, 84
sacral, of cord, 16
of sixth nerve, 63

atrophy .of, 100
spinal accessory, 20, 55
of superficial arched fibres, 59
tegmental, 93, 94, 103
of third nerve. See NUCLEUS, OCULO-
MOTOR.

upper, of fillet, 104
vagus, 55

accessory, 55
of white matter of cerebellum, 83

OBEX (bolt), 50
Occipital gyri, 152
index, 151
lobe, 112, 119, 145, 151, 153, 163, 164,

165, 166, 177, 180, 195
effect of removal, 32
operculum, 144

pole of hemisphere, 137, 152, 178
region of cortex cerebri, effect of removal,

no

sinus, 183

sulcus, anterior, 144, 152
lateral, 151, 152
transverse, 150, 152
Occipito-temporal annectent gyrus, 152
region of cortex, 136
Ocular muscles, innervation of, 99, 119
Oculomotor nucleus. See NUCLEUS.

sulcus, 100

Olfactory bulb, 145, 159, 174, 195
bundle of cornu Ammonis, 1 58
cells, 176

chiasma (xidfa, mark with letter X), 160
glomeruli (dim. of glomus, clue of thread),

175. 176

lobe, 145, 158, 159, 164, 174
lobule, anterior, 159, 160

posterior, 159
nerves, 159, 175
nerve-fibres, layer of, 175, 176
root, inner or mesial, 128, 156, 158, 159, 160
outer or lateral, 156, 159, 160
middle or grey, 159, 160
upper or dorsal, 160
sulcus. 149

tract, 145, 156, 158, 159, 160, 164, 174
Olivary body, 41, 45, 85
nucleus. See NUCLEUS.
peduncle, 56
Olive, inferior, 41. 45, 86, 93, 94, 118

connection with cerebral cortex,

86
superior, 47, 60

Operculum (cover or lid) of Burdach, 141
frontal, 142
fronto-parietal, 142
of hypophysis, 182
occipital, 144
orbital, 142
temporal, 142
Optic lobes, 38

of birds, 107
chiasma, 96, 117, 198
commissure, 117
ganglion, 109

basal, 1 1 6, 120
optic nerve, 93, 118, 188
radiations, 112
recess, 97
thalamus, 93, 96, 97, no, 122, 136, 163,

164, 1 66, 195, 197
effect of lesion, 85
inferior peduncle of, 164
tract, 96, 105, 107, no, in, 112, 114, 117,

164

connection with cerebellum, 120
Orbital gyri, 149

limbs of Sylvian fissure, 142

muscles, innervation of, 99, 119

sulcus, 149

surface of cerebral hemisphere, 145, 148;

149, 195
Origin of nerves from medulla oblongata, 40

spinal nerves, 3, 19
Osmatic (oer/uaojuoi, smell) mammals, 158, 159,

160, 161

Outlying cells of cord, 17
Oval lobule, 149

PACCHIONIAN glands, 190

granulations, 184
Pachymeninx (iraxvs, thick ; MV'7l» membrane),

181
Paracentral fissure, 145

lobule, 149, 150
Parallel fissure, 153
Paramesial sulcus, 146, 147, 161
Parietal convolutions, 151

ascending, 143, 148, 150,

151, 163
foramen, 115

lobe, 112, 145, 149, 155, 177, 180, 195
lobules, 150, 151, 152, 166
Parieto-occipital annectent gyrus, 151, 152

fissure, 124, 143, 144
Parkes on brain of negro, 161
Paroccipital fissure, 150
Pars ascendens inferior s. postceutralis inferior

of intraparietal sulcus, 150
superior of intraparietal sulcus,

ISO

basilaris of third frontal gyrus, 147, 148
fronto-parietal is of operculum, 142
horizontalis s. posterior of intraparietal

sulcus, 150, 152

intermedia of facial nerve, origin of, 55
occipitalis of intraparietal sulcus, 150
olfactoria of olfactory bundle, 158, 164
orbitalis of operculum, 142

of third frontal gyrus, 147
temporalis of olfactory bundle, 158, 164
triangularis of operculum, 142

third frontal gyrus, 147
Partitions of dura mater, 182
Paulier on grey cortex, 177

INDEX AND GLOSSARY TO VOLUME III. PART I.

215

Peacock on brain-weight, 178
Peduncle (pednnculus, foot-stalk of leaf) or
peduncles, of cerebellum, 38, 46, 84
inferior, 69, 83, 86, 93, 95, 118
middle, 38, 46, 67, 70, 83, 85, 93, 94, 164
superior, 67, 69, 82, 83, 84, 93, 94,

100, 103, 164, 195
of cerebrum, 96, 100, 135
of corpus albicans, 115
of corpus callosum, 128, 155, 158, 159
olivary, 56

of pineal body, 113, 114, 117
of thalamus, inferior, 164
Peduncular tract, 65
Pedunculus conarii, 1 14

flocculi, 76, 82

Perforated space or lamina, anterior, 112, 131,
135, 141,155,158,
159, 165, 197
posterior, 96, 98,

"5, 195

Perineural sheaths, 188
Peripheral venules, 193
Peri vascular sheath, 186, 187
Perpendicular fasciculus, 165

fissure, external, 144
Pes (foot) accessorius, 127
hippocampi, 124
pedunculi, 100
Petrosal sinus, superior. 182
Phrenic nerve, origin of, 16
Pia mater (pia, translation of Arabic word,
meaning properly thin ; mater, see Dura
mater), I, 3, 100, 114, 122, 137, 181,
184
Pillars of fornix, anterior, 97, 113, 116, 129,

131, 158
posterior, 124, 129, 130, 157,

158
Pineal (pinea, pine-cone) body or gland, 96, 97,

104, 114

peduncles of, 113, 114, 117
eye, 115
recess, 97
stria, 98, 114, 129
Pituitary body, 96, 97, 116
Plexuses, choroid, of fourth ventricle, 50, 98,

185, 186, 195
of lateral ventricles, 122,

124, 155, 185, 198
sand of, 114
of third ventricle, 98, 185,

198

white, of cerebral cortex, 169
Pneumo-gastric nerve. See NERVE, VAGUS.

nucleus. See NUCLEUS. VAGUS.
Pole of hemisphere, 137, 147, 152, 178
of island, 155
of temporal lobe, 153
Polymorphous cells, layer of, 168
Pons (bridge) Varolii, 38, 46, 100, 101, 118, 179
blood-supply of, 194
dimensions of, 40
external characters of, 38,

46

internal structure of, 60
literature of, 67
nuclei of, 60, 86, 93
structure of, 47
transition to mid-brain

from, 65
Ponticulus (dim. of pans], 46

Postcentral gyrus, 150

lobule, 154, 155, 156

sulcus of cerebellum, 71, 73, 79, 82

of cerebrum, 143, 150
Postclival fissure, 71, 73, 79, 82
Posterior area of medulla oblongata, 41, 43

calcarine fissure, 144

central gyrus, 150

columns of cord, white, 9, 26, 27, 29, 32,

53, 63

vesicular, 16

of medulla oblongata, 41, 104
commissure of cerebrum, 38, 98, 104, 109,

114, 117, 119
of cord, 7, 18

cuneo-lingual annectent gyrus, 144
descending tract, 29
horn or cornu of cord, 8, 10, 52, 53, 104

of lateral ventricle, 122, 124
intermediate septum of cord, 7
limb of Sylvian fissure, 141, 142
lobe of pituitary body, 116
longitudinal bundle, 58, 65, 66, 86, 93, 94,

95, 99, IO2> IO9, 114, H9

olfactory lobule, 159

orbital gyrus, 149

pillars of fornix, 124, 129, 130, 157, 158

segment of internal capsule, 136

septum of cord, 7, 188

spinal artery, 192

tubercle of optic thalamus, no
Postero-lateral column of cord, 7, 28, 44
Postero-mesial column of cord, 7, 10, 28, 43
Postgracile sulcus, 75
Postnodular fissure, 75, 79
Postparietal gyrus, 151, 152, 153
Postpyramidal fissure, 75, 79
Precentral gyrus, 147, 148

lobule, 154, 155

sulcus of cerebellum, 71, 73, 79

of cerebrum, 143, 145, 146, 148,

155

transverse, 143, 146, 155
Preclival fissure, 71, 73, 79, 82
Precuneate sulci, 151
Precuneus, 151

Prefrontal region of cortex, 136, 163
Pregracile sulcus, 75
Prelimbic fissure, 145
Prepyramidal fissure, 75, 79
Pre-Rolandic sulcus. 145
Primates, third frontal gyrus of, 148
Process, intermediate, 8

vermiform, 69, 71, 73, 74, 77, 78
effects of removal, 94
Processes of dura mater, 182
Processus reticularis, 8
Projection fibres, 163, 164, 169, 172
Proseucephalon (irpos, before ; eyKf<fia\oi', brain),

122

Psychomotor (tyvxh, mind ; motio, motion)

centres, 163, 172
Pulvinar (cushion), no, 117, 119
Purkinje, corpuscles or cells of, 87, 88, 91, 93

on nerves of pia mater, 187
Putamen (husk), 134, 197
Pyramid of worm, 74, 76, 79
Pyramids, anterior, 43, 45

decussation of, 46

large and small, layers of, 168

posterior, 44
Pyramidal bundles, 67, 93

216

INDEX AND GLOSSARY TO VOLUME III. PART I.

Pyramidal nuclei, 57

tract, 93, 100, 101, 163, 164, 172

anterior or direct, 24, 31, 32, 45
of isthmus, 65

lateral or crossed, 24, 31, 32, 51, 64
section of, 31

QUADRATE lobule, 149, 151, 156
Quadrigeminal bodies, 38, 96, 104, 109, no,

117, 119, 164, 195
Quadrilateral lobe of cerebellum, 74
Quadrumana, anterior occipital sulcus of, 152

calcarine fissure of, 144

intraparietal sulcus of, 150

occipital lobe of, 151

parieto-occipital fissure of, 143

third frontal gyrus of, 148
See also MONKEY.

RABBIT, pyramidal tract of, 25

Racial variations in gyri and fissures, 161

Randwindung (German, bordering convolution),

Raphe (^cw/)^, seam) of bulb and pons, 59, 60

of corpus callosum, 127

of midbrain, 100
Raphe-root of fifth nerve, 62
Rat, pyramidal tract of, 25
Recess, lateral, 47, 48, 49, 188

optic, 97

pineal, 97

suprapineal, 97

Recti muscles of eye, innervation of, 99
Red nucleus, 103, 114
Reid, J., on brain-weight, 178
Reid, R. W., on relation between vertebral

spines and nerve-origins, 3
Reil, island of, 133, 141, 145, 154, 164
Relative weight of encephalon to body, 178 -
Reptiles, pineal body of, 115

posterior longitudinal bundle of, 103

segmentation of spinal cord of, 16
Restiforrn (restis, rope) body, 44, 69, 85, 86
Reticular formation, 51, 52, 58, 60, 65, 100,

ipi, 102, 103, 114, 164
Reticulated white substance, 167
Retina, 107, 118, 119
Retinal fibres, no
Retzius, on cisternse arachnoidales, 188

on septum posticum, 188
Rhinencephalon (f>is, f>ivos, nose ; ^yKt(j>a.\ov,

brain), 160, 161

Ridge, connecting, of pyramid, 76
Rivi (streams) and rivuli, 188
Rolandic angle, 143

gyrus, 143

region of cortex, 136
Rokndo, fissure of, 143, 150, 154, 155

funiculus of, 44, 52

substantia gelatinosa of, 8, 10, 13, 44
cells in, 17

tubercle of, 44, 52, 62
Roller on auditory nerve-roots, 56
Roof, ganglion of, 108
Roots, of auditory nerve, 56, 63

of facial nerve, 63

of filth nerve. See NERVE.

olfactory, inner or mesial, 128, 156, 158,

159, 1 60
middle, 160
outer or lateral, 156, 159, 160

Roots — continued.

olfactory, upper or dorsal, 160

of optic tract, 117

of spinal nerves. See NERVE-ROOTS.

of third nerve, 100
Rostral sulci, 149

Rostrum (beak), of corpus callosum, 128
Rust-coloured layer of cerebellar cortex, 87

SACHS on medullary centre of occipital lobe, 166
Sacral nucleus, 16
Sacro-coccygeal region of cord, 10
Sacro-lumbar nerves, effect of section of posterior

roots, 27

Sagittal sulcus of midbraiu, 104
Sala on fascia dentata, 173
Sandwich islanders, brain- weight of, 180
Schwalbe on falciform lobe, 155
on tsenia semicircularis, 131
Sclavonic races, brain-weight of, 180
Sclerosis (aK\rip6s, hard), 24
Second nerve. See NERVE, OPTIC.
Secondary degeneration of nerve-fibres, 24
Section, effects of, of fillet, 53

of nerve-roots, dorsal and cer-
vical spinal.28
sacro - lumbar

spinal, 27
sensory of fifth

nerve, 53

of pyramidal tract, 31
of spinal cord, 32
Segment of spinal cord, 3, 16
Semicircular fibres, 85
Semilunar lobe, inferior, 74, 77, 82
Sensory nuclei. See NUCLEUS OF FIFTH NERVE.
root of fifth nerve, 53
tract, direct. 163
Septa of cord, 7, 9, 12
Septum lucidum (clear partition), 122, 128, 129,

155. 159

posterior intermediate of cord, 7

posticum of cord, 7, 188
Seventh nerve. See NERVE, FACIAL.

nucleus of. Sen NUCLEUS, FACIAL.
Sexual differences in brain-weight, 178, 179, 180

variations in gyri and sulci, 161
Sheath, perineural, 188

peri vascular, 186, 187
Sherrington on degeneration after cortical lesions,

32

on outlying cells of cord, 1 7
Short association fibres, 165

degenerations, 32
Siliqua (capsule) olivse, 45
Sims on brain- weight, 178
Singer on degenerations in spinal cord, 34

on section of nerve-roots, 27

on tracts of Burdach, 32
Siuus (hollow) lateral, 182, 184

longitudinal, inferior, 182

superior, 152, 182, 184, 191

occipital, 183

petrosal, superior, 183

straight, 182, 184
Sinuses of dura mater, 182
Sixth nerve. See NERVE.

nucleus of, 63

Size of body, influence of, on convolutions, 162
Slender lobe, 74, 77
Smooth brains, 162

INDEX AND GLOSSARY TO VOLUME III. PART 1.

217

Soft commissure, 97
Solitary bundle, 63

cells, 17

Solly on fibres of anterior column, 65
Space, epidural, 182

perforated, anterior, 112, 131, 135, 141,

»55, 158, 159, 165, 197
posterior, 96, 98, 115, 195

subarachnoid 3, 186, 187, 198

subdtiral, 3, 181, 184
Special senses, centres for, 163
Speech-centre, 147
Spencer on pineal eye, 115
Sphincter pupillse, innervation of, 99
Spinal accessory nerve, 16, 20, 40

nucleus, 20, 55
Spinal arteries, 191, 192
Spinal bulb. See MEDULLA OBLONGATA.
Spinal cord or marrow, I, 2

blood-supply of, 191

cell-columns of. See CELL-COLUMNS.

central canal of, 9, 10, 19

central ligament of, 2, 5

columns of, white. See COLUMNS.

commissures of, i, 6, 7, 10, 18, 34

conducting tracts of, 22

connective tissue of, 9

course of nerve-tibres in, 22

degenerations in, 27

dimensions of, 2, 3

distribution of nerve-cells of, 14

enlargements of, 3, 5

features of different regions of, 10

fibres of, traced through bulb and pons, 63

fissures or furrows of, 6, 7

form of, 3

grey matter of, 7, 13

See also GREY MATTER.

internal structure of, 7

lesions of, 32

lymphatics of, 198

membranes of, i, 3, 181

microscopic structure of, 12

neurilemma of, 186

neuroglia of, 12

origin of nerves from, 3, 1 1

proportions of grey and white matter in. 7, 10

relation of to vertebrae, 2

segments of, 3, 16

septa of, 7, 9, 12, 188

veins of, 193

weight of, 1 80

white matter of, 9, 12
Spinal nerves, 3, 11, 19, 94
Spitzka on mesial fillet, 101
Splenium (ffirXyviov, pad), 128
Stalk of thai amus, anterior, 112

lower, 112

Stammtheil (German, stem-part), 154
Starr on oculomotor nucleus, 99
Stature, influence of, on brain-weight, 179
Stem of hemisphere, 154
Stieda on optic lobes of birds, 107
Stilling on decussating fibres of cerebellum, 84

on optic tract, 118

on restiform body, 85
Straight sinus, 182, 184
Stratum albo-cinereum (white-grey layer), infe-

rius, 107
superius, 107

cinereum, 107

dorsale, 114

Stratum — continued.

granulosum, 174

intermedium, 101

laciniosum (jagged), 173

lemnisci, 107

opticum, 107

radiatum, 173

zonale, 98, 107, in
Stria (furrow, streak) alba tuberis, 116

medullaris, of mid-brain, 98

pinealis, 98, 114, 129

terminalis, no, 122
Striae, longitudinal, lateral or grey, 127, 155,

157, 158
mesial, 127, 128, 155, 157,

158

medullares seu aeusticse, 50, 59, 94
Subarachnoid fluid, 187

space, 3, 186, 187, 198
Subcalcarine gyrus, 153
Subdural space, 3, 181, 184
Subiculum (support) cornu Ammonis, 1 56
Substantia ferruginea (colour of iron-rust),

5i, 65
gelatinosa of Rolando, 8, 10, 13, 44, 62

cells of, 17
centralis, 18
innominata, 112, 135
interansalis (between the loops), 112, 114
nigra (black), 114
reticularis alba, 156
spongiosa, 13
Subthalamic tegmental region, 112, 113, 122,

136, 164

SULCUS (furrow) or SULCI (see FISSURES), causa-
tion of, 162
of cerebellum, 71, 75, 77

arcuate, anterior, middle and posterior,

75. 77
horizontal, great, 71, 75, 79, 82

lower or lesser, 75, 77
midgracile, 75
postcentral, 71, 73, 79, 82
postgracile, 75
postnodular, 75, 79
postpyramidal, 75, 79
precentral, 71, 73, 79
pregracile, 75
prepyramidal, 75» 79
vallecula?, 75, 76
of cerebral hemispheres, 137, 145, 149, 151,

153, 154, 156
callosal, 127, 156
central, 143
centralis insulae, 154
diagonalis, 146, 148
extremus, 144
fimbrio-dentate, 157
frontalis inferior, 146, 148

medius, 146, 147, 161

mesialis, 149

(of Cunningham), 146, 147

superior, 146, 148
fronto-marginalis, 146

lateralis, 146, 149
fronto-orbitalis, 149
H-shaped, 149
inferior transverse, 143
intraparietal, 149, 155
limitans insult, 154
inarginalis, 149
occipitalis anterior, 144, 150, 152

218

INDEX AND GLOSSARY TO VOLUME III. PART I.

SULCUS or SULCI — continued.

of cerebral hemispheres — continued.
occipitalis lateralis, 151, 152

transversus, 150
olfactory, 149
orbitales sagittales, 149
orbitalis, 149

transversus, 149
paramesial, 146, 147, 161
postcentralis, 143, 150
postcentralis insult, 155
postcentralis superior, 150
postlimbic, 155
precentralis, 143, 145, 155

inferior, 146, 148
insulte, 155
mesialis, 145
superior, 146

transversus, 143, 146, 155
precuneati, 151
pre-Rolandic, 145
radiatus, i46

rectus (straight) Quadrunianorum, 148
retrocentralis transversus, 150
rostral, 149
supraorbital, 149
temporal, 153
transversus anterior, 146
inferior, 143
occipitalis, 150
orbitalis, 149

precentralis, 143, 146, 153
retro-centralis, 150
triradiate, 149
of mid-brain, lateralis, 100

longitudinalis, 104
oculomotorii, 100
sagittalis, 104
transversus, 104

of spinal cord, intermediate, 7, 24
Sunken surface of cortex cerebri, 137, 177
Superficial arched fibres, 44, 45, 58, 59
Superior commissure of cerebellum, 84
fovea, 50
medullary velum, 47, 70, 73, 79, 82, 85,

98, 103, 104
olive, 47, 60
petrosal sinus, 183
worm, 69

Supracallosal gyrus, 155, 158
Supramarginal gyrus, 151, 153
Supraorbital sulcus, 149
Suprapineal recess, 97
Surfaces of cerebellum, Ji, 74

cerebral hemispheres, 137, 197
orbital, 145, 147, 148, 149, 195
Sylvian angle, 142
aqueduct, 96

fissure, 141, 143, 146, 147, 148, 150
fossa, 142

TABLE of parts of cerebellar worm and hemi-
spheres, 78
Tsenia (ratvia, band) of mediilla oblongata, 49

fimbvise, 158

fornicis, 98, no, 114, 129

hippocampi, 130

pontis, 115

semicircularis, 122, 124, 129, 131
Tseniae tectse (concealed), 127
Tapetum (carpet), 124, 129

Tartuferi on quadrigeminal bodies, 106
Tegmental nucleus, 93, 94, 103
Tegmentum (covering), 98, 100, 102, 112, 114,
115, 163, 164

subthalamic, 112, 113, 122, 164
Tela choroidea (choroid web) inferior, 185, 186,
1 88

superior, 185
Temporal division of cerebral hemisphere, 1 37

gyri, 151, 152, 153, 155

lobe, 112, 145, 149, 152, 156, 160, 163,
164, 165, 177, 180, 195

operculum, 142

sulci, 153

Temporo-occipital bundle, 165
Temporo-sphenoidal lobe, 152
Tent of dura mater, 182

fourth ventricle, 78
Tenth nerve. See NERVE, VAGUS.
Tentorium (tent) cerebelli, 182

of hypophysis, 182
Terminal arteries, 193

filament of cord, 5, 189
Tertiary degeneration of nerve-fibres, 24
Testes, 105

Testut on tsenia semicircularis, 131
Teutonic races, brain- weight of, 180
Thalamencephalon (thalamus, bed ; tyKi<j>a\ov,

brain), 96

Thalamus, optic. See OPTIC THALAMUS.
Theca (sheath), 3, 182
Thickness of cerebral cortex, 177
Third nerve. See NERVE.
Third ventricle, 96, 97
Threshold of island, 155
Tiedemann on brain- weight, 178
Tomentum (flock of wool, hair, &c.) cerebri, 184
Tonsil of cerebellum, 74, 76
Tooth on origin of facial nerve, 61
Trabs (beam) cerebri, 127

Tract or tracts, antero-lateral ascending, 24, 25,
32, 34, 65, 85, 103, 104

of antero-lateral column, 24

antero-lateral descending, 24, 25, 32, 65,
85, 86

bulbar ascending cerebellar, 86

of Burdach, 26, 28, 32, 44

central, of fifth nerve, 62
of tegmentum, 60

comma, 26, 29, 32

conducting, of cord, 22

crossed or lateral pyramidal, 24, 31, 32,

51, 64

direct pyramidal, 24, 31, 32, 45
sensory, 163

cerebellar, 24, 25,32, 34, 44, 65. 85, 86
dorso-lateral ascending, 24, 25, 32, 34, 44,

65, 85, 86
of fillet, 103

of Goll, 26, 28, 32, 34, 43
intermedio-lateral, 8
of Lissauer, 20, 26, 29
olfactory, 145, 156, 159, 160, 164, 174
optic, 96, 105, 107, no, in, 114, 117, 164

connection with cerebellum, 120
peduncular, 65
posterior descending, 29
of posterior white columns, 26
pyramidal, 24, 31, 32, 45, 93, 101, 163,

164, 172
of isthmus, 65
Tractus trausversus pedunculi, 118

INDEX AND GLOSSARY TO VOLUME III. PART I.

219

Transition from pous to mid-brain, 65

Transitional tegmental region, 114

Transverse fibres of cerebral hemisphere, 163, 164

fissure, 124

gyri. Sec GYRUS.

sulcus, inferior, 143

of mid-brain, 104
occipital, 150, 152
preceutral, 143, 146, 155

temporal gyri, 153
Trapezium, 47, 104
Trapezoidal body, 73, 78, 79, 82
Trigeminal nerve. See NERVE, FIFTH.
Trigonum (triangle) acustici, 50

habenulee, in, 113, 114

hypoglossi, 50

interpedunculare, 100

olfactorium, 159, 160

vagi, 50

ventriculi, 127
Triradiate sulcus, 149
Trochlear nerve. See NERVE, FOURTH.
Trophic fibres of fifth nerve, origin of, 51
Tuber (swelling) annulare, 39

cinereum, 96, 98, in, 116

posticum, 74, 77, 79

val villa; s. posticum, 74, 77, 79
Tubercle, acoustic, 50

cuneate, 44

of optic thalamus, anterior, no
posterior, no

of Rolando, 44, 52, 62
Tnberculum laterale s. acusticum, 50
Tiirck, column of, 24

Turner, W. A. on origin of facial nerve, 61
Turner, Sir W. on rhinencephalon, 161
Twelfth nerve. See NERVE, HYPOGLOSSAL.

UNOINATE gyrus, 156, 172

fasciculus, 165
Uncus (hook), 156, 158

Uvula (from resemblance to uvula of soft palate),
74, 76, 79

VAGAL nucleus, accessory, 55

Vagus (wandering) nerve. See NERVE.

Vallecula (dim. of vallis, valley), 70

subi of, 75, 76

Sylvii, 137, 141, 158, 159
Valve of Vieussens, 47, 70, 195
Variations in gyri and sulci, 161
Vein, ehoroid, 185

of corpus striatum, 122, 185

of Galen, 185
Veins of dura mater, 184

of spinal cord, 193

Velum (sail or curtain) interpositum, 98, 114,
122, 129, 185, 198

medxillary, inferior, 48, 70, 76, 78

Velum — continued.

medullary, superior, 47, 70, 73, 79, 82, 85,

98, 103, 104
Vena mngna Galeni, 186

Ventricles of brain, 38, 47, 96, 97, 122, 188, 189
of cerebral hemispheres, 122
fourth, 47, 73
floor of, 50
tent of, 78
lateral, 97, 122
of septum, 129
third, 96, 97

Ventro-lateral cell-group of anterior horn, 14
tract, ascending, 24, 25, 32, 34, 65, 85, 103

104

descending, 24
Venules, central, 193

peripheral, 193

Vermiform (vcrmis, worm) process. See WORM.
Vicq-d'Azyr, bundle of, 113, 115, 129, 166

line of, 167

Vieussens, valve of, 47, 70, 195
Villi (villus, tuft of hair), choroidal, 186

arachnoidal, 184, 190
Visual area of cortex cerebri, no

centres, connection with cord and bulb, 119
oculomotor nuclei,

119

interconnection of, 119
Voelckers, on oculomotor nucleus, 99
Volkmann, on nerves of arachnoid, 189

WAGNER on grey cortex, 1 76
Weight of brain, 178
spinal cord, 180
Weisbach on orbital sulcus, 149

weight of brain, 178
Wernicke on nucleus caudatus, 132
Westphal and Edinger, nucleus of, 99
White columns of cord. See COLUMNS.
commissure of cord, 6, 10
matter of cerebral hemispheres, structure

of, 163
cord, 9

microscopic structure of, 12
proportion of to grey, 7, 10
plexuses, 169
substance of cerebellum, 71, 78, 87, 91

commissural fibres in, 84
nuclei in, 83

Worm, 69, 71, 73, 74, 77, 78
effects of extirpation, 94

ZONA incerta, 1 14

Zuckerkandl on bordering gyri, 159

olfactory bundle, 158
gyrus geniculi, 1 58
supracallosus, 158
subcallosus, 159

END OF PART I.

BRADBURY, AGNKW, & CO. LD., PRINTERS, WHITEFRIARS.

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