Difference between revisions of "Talk:Book - Buchanan's Manual of Anatomy including Embryology 14"

From Embryology
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see of the occipital bone, and locking takes place. In complete forward or  
 
see of the occipital bone, and locking takes place. In complete forward or  
 
ntral flexion the anterior margins of the superior articular processes of the  
 
ntral flexion the anterior margins of the superior articular processes of the  
as come into contact with the occipital bone in front of each condyle.  
+
as come into contact with the occipital bone in front of each condyle.
 
 
 
 
==CHAPTER XV THE NERVOUS SYSTEM==
 
 
 
 
 
The nervous system is arranged in two main divisions, cerebro-spina
 
and autonomic; this last contains the sympathetic and the parasym
 
pathetic.
 
 
 
The sympathetic system consists of two gangliated cords situate*
 
on either side of the vertebral column, and three main prevertebra
 
plexuses: the cardiac situated in the thorax; the epigastric or solar
 
and the hypogastric plexus, the latter two being situated in th
 
abdomen; subsidiary plexuses are associated with these.
 
 
 
The parasympathetic system includes cranial and sacral outflows
 
leaving the cerebro-spinal axis through certain nerves without joininj
 
the sympathetic cords.
 
 
 
The cerebro-spinal nervous sytem or axis consists of the encephaloi
 
and the spinal cord, the former being situated within the crania
 
cavity, and the latter within the spinal canal. The continuity betwee;
 
these two divisions is established through the foramen magnum.
 
 
 
The cerebro-spinal axis is central in position, and is connecte*
 
with the various parts of the body by the cranial and spinal nerves
 
It is composed of two kinds of nervous matter, white and grey. Th
 
white matter consists chiefly of nerve-fibres, and the grey matter c
 
nerve-cells, with their axis-cylinder processes or axons and dendrites
 
the pervading supporting tissue in each case being called neuroglk
 
In the spinal cord the white matter is disposed externally, whilst th
 
grey matter is situated in the interior. In the brain there is the sam
 
arrangement of grey matter in the centre, surrounded by white mattei
 
but a third and more modern layer of cortical grey matter has bee
 
added to the surface of the white, a layer which is unrepresented i
 
the spinal cord.
 
 
 
The cerebro-spinal axis is surrounded by three membranes, c
 
meninges , which, from without inwards, are named the dura matei
 
arachnoid membrane, and pia mater.
 
 
 
 
 
THE SPINAL CORD.
 
 
 
Membranes of the Spinal Cord. —The membranes are three: th
 
dura mater, the arachnoid membrane, and the pia mater.
 
 
 
Dura Mater. —This is the most external covering of the cord. I
 
forms a dense fibrous tube, known as the theca, which extends fror
 
the margin of the foramen magnum of the occipital bone to the lowe
 
level of the second sacral vertebra. Inferiorly, where it has becom
 
 
 
1410 1
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1411
 
 
 
 
 
Frontal Lobe
 
 
 
 
 
Temporal Lobe
 
 
 
/. Basilar Artery
 
Vertebral Arteries
 
 
 
 
 
[■six
 
 
 
 
 
j -— Superior Cervical Sympathetic
 
/ Ganglion
 
 
 
 
 
1>. Cervical Plexus
 
 
 
■j -Vertebral Artery
 
 
 
i-Middle Cervical Ganglion
 
 
 
Brachial Plexus
 
ist Thoracic Ganglion
 
 
 
 
 
4th Intercostal Nerve
 
Anterior Spinal Artery
 
 
 
 
 
U_ Thoracic Sympathetic Cord
 
 
 
 
 
 
 
 
 
 
 
 
 
. Spinal Ganglion
 
 
 
 
 
Subcostal Nerve
 
 
 
 
 
L-. Lumbar Sympathetic Cord
 
 
 
 
 
Lumbar Plexus
 
 
 
 
 
Pelvic Sympathetic Cord
 
 
 
 
 
^— Sacral Plexus
 
 
 
 
 
Ganglion Impar
 
 
 
 
 
Eig. 859.—The Cerebrospinal and Sympathetic Systems (Anterior
 
 
 
View) (Hirschfeld and Leveille).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1412
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
tapering behind the second sacral vertebra, the theca is perforate
 
by the filum terminale, and from this level the spinal dura mater i
 
prolonged downwards around the filum terminale, with which it blend:
 
Finally, it is attached, along with the filum terminale, to the bac
 
of the first coccygeal vertebra, where it is incorporated with th
 
periosteum. In this situation the spinal dura mater is firmly fixed.
 
 
 
The theca surrounds the spinal cord very loosely, and it is separate
 
from the wall of the spinal canal by an interval, called the extra-dur;
 
space, which is occupied by venous plexuses and loose areolar tissue.
 
 
 
Opposite the intervertebral foramina of each side the theca has
 
series of openings, which are arranged in two parallel rows. Th
 
openings constituting each pair are placed side by side, but are distinc
 
from each other, and they transmit the ventral or anterior and dors;
 
or posterior roots of the spinal nerves. Each of these roots, as it make
 
its exit, receives a tubular sheath from the margin of the corresponds
 
thecal opening, and these sheaths remain distinct as far as the spin;
 
ganglion of the dorsal root. After this the neighbouring sheath
 
form one which blends with the sheath of the corresponding spin;
 
nerve.
 
 
 
The spinal dura mater is maintained in position by several cor
 
nections. (i) Superiorly it is fixed to the margin of the forame
 
magnum of the occipital bone. (2) Opposite the body of the ax:
 
it is firmly attached anteriorly ’ to the posterior occipito-axial ligamen
 
(3) Below the level of the axis it is loosely connected anteriorly wit
 
the posterior longitudinal ligament of the bodies of the vertebrae b
 
fibrous bands. (4) Laterally it is connected with the sheaths of th
 
spinal nerves by means of the tubular sheaths which it gives to th
 
ventral and dorsal nerve-roots. (5) Inferiorly it blends with th
 
periosteum over the back of the first coccygeal vertebra through th
 
filum terminale. Posteriorly it is quite free from connections.
 
 
 
The spinal dura mater differs from the cranial dura mater in th
 
following respects: (1) It is destitute of an outer or periosteal layei
 
(2) it does not send septa into the spinal cord; and (3) it does nc
 
contain venous sinuses.
 
 
 
Blood-supply of Spinal Dura Mater.—The arteries are derive
 
from (1) the spinal branches of the vertebral, intercostal, and lumba
 
arteries; and (2) the lateral sacral arteries, which are branches of th
 
internal iliac artery.
 
 
 
Nerve-supply.—The nerves are partly spinal and partly sympatheth
 
 
 
Lymphatic Vessels.—There are no lymphatic vessels, their plac
 
being taken by perivascular lymph-spaces in connection with th
 
arteries.
 
 
 
Structure. —The spinal dura mater consists of fibrous tissue and some elast:
 
tissue disposed in parallel longitudinal bundles. Its internal and extern;
 
surfaces are covered by endothelial cells.
 
 
 
Subdural Space.—Between the spinal dura mater and the arachnoi
 
there is a narrow cleft-like interval, which is known as the subduri
 
space. It contains a small amount of fluid, and communicates freel
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
T 4 X 3
 
 
 
 
 
Dura Mater (Theca)
 
 
 
 
 
—-Arachnoid
 
 
 
 
 
h the lymph-spaces or clefts in the sheaths of the spinal nerves,
 
has, however, no communication with the subarachnoid space.
 
Spinal Arachnoid Membrane.—This is a delicate transparent
 
mbrane which loosely surrounds the spinal cord between the theca
 
ernally and the pia mater internally. It is separated from the
 
:ca by the subdural space, and from the pia mater by the sub.chnoid space. Superiorly it is continuous with the cranial arachd, and inferiorly it encloses the cauda equina. On either side it
 
ms sheaths for the processes of the ligamentum denticulatum as
 
as the inner surface of
 
» theca. The ventral and
 
:sal roots of the spinal
 
:ves also receive sheaths
 
m it, which accompany
 
un through the openings
 
the theca, but soon cease.
 
 
 
It is of practical importce to remember that the
 
ichnoid membrane usually
 
Is at the lower level of the
 
iond sacral vertebra, and
 
ver extends lower than the
 
ird.
 
 
 
Subarachnoid Space (Ca- ,
 
m Subarachnoidale).—This l
 
ice, which is wide, is
 
uated, as stated, between
 
s arachnoid and pia mater,
 
contains cerebro-spinal
 
 
 
id, and its dorsal part is
 
 
 
ntinuous superiorly with Fig - 86 °- Portion of the Spinal Cord,
 
 
 
- rerebello rnednllarv cis- showing the Membranes, Ligamenta
 
o LEiEDEiio-iiiEuuiiaiy Lis Denticulata, and Roots of the Spinal
 
 
 
"na of the cranial sub- Nerves.
 
 
 
ichnoid space, which com
 
micates with the fourth ventricle by the ‘ foramen of Magendie,’
 
e median aperture of the roof.
 
 
 
The subarachnoid space is partially divided into two compartmts, ventral and dorsal, by ligamenta denticulata, which form inmplete lateral septa. The ventral roots of the spinal nerves traverse
 
e ventral compartment, and the dorsal roots the dorsal compartsnt. The dorsal compartment is partially subdivided into two
 
•rtions, right and left, by means of a third incomplete septum, called
 
e posterior septum. This partition extends from the pia mater as
 
crosses the dorsal median fissure of the spinal cord to the dorsal
 
-rt of the arachnoid at the median line. All the compartments of
 
 
 
 
 
 
 
Ligamentum Denticulatum
 
 
 
-Anterior Nerve-Root
 
 
 
Posterior Nerve-Root
 
Pia Mater
 
 
 
 
 
_ Spinal Cord
 
 
 
 
 
Anterior Nerve-Root (cut)
 
 
 
 
 
e subarachnoid space communicate freely with each other.
 
 
 
The subarachnoid space has no communication with the subdura
 
ace.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1414
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Structure of the Arachnoid Membrane. —The arachnoid consists of fine fibrou
 
tissue arranged in interlacing bundles, the intervals between these bundle
 
being occupied by delicate cellular membranes. Several such layers, intimatel
 
blended together, form the membrane.
 
 
 
Beneath the arachnoid, and constituting a part of it, there is a reticulum c
 
subarachnoid trabeculce. These trabeculae consist, as in the case of the arachnoi
 
proper, of fine fibrous tissue, but the intertrabecular spaces, instead of bein
 
occupied by cellular membranes, contain cerebro-spinal fluid. The trabecula
 
reticulum connects the arachnoid with the subjacent pia mater, and varie
 
greatly in density in different parts.
 
 
 
 
 
Spinal Pia Mater.—This is the deepest membrane of the spins
 
cord. It is definitely fibrous and very vascular, and closely invest
 
 
 
the cord. Superiorly it is con
 
 
 
 
 
 
 
A] Dura Mater (Theca)
 
 
 
 
 
. Linea Splendens
 
 
 
 
 
Ligamentum Denticulatuir.
 
 
 
 
 
Pia Mater
 
 
 
 
 
J_L \nterior Nerve-Root
 
 
 
 
 
Fig. 86i.—A Portion of the Spinal Cord
 
(Anterior View).
 
 
 
The theca has been laid open, and the
 
arachnoid membrane removed.
 
 
 
 
 
tinuous with the cranial pi
 
mater, and inferiorly it is pro
 
longed from the conus medul
 
laris over the upper half of th
 
intrathecal part of the filur
 
terminate. On either side i
 
forms tubular sheaths for th
 
ventral and dorsal roots of th
 
spinal nerves, which blend wit]
 
the sheaths of the nerves.
 
 
 
Along the course of th
 
ventral median fissure of th
 
cord it sends a vascular fob
 
into that fissure. Along th
 
course of the dorsal medial
 
fissure, over which it passes
 
the neuroglial septum occupy
 
ing that fissure is attached t<
 
it. From the deep orifice o
 
the pia mater several septa ar
 
 
 
 
 
prolonged into the cord, which carry with them portions of the glia
 
sheath.
 
 
 
The pia mater is separated from the arachnoid by the subarach
 
noid space, and opposite the dorsal median fissure of the cord it i
 
connected with the dorsal part of the arachnoid by the posterio
 
subarachnoid septum.
 
 
 
Blood-supply.—The pia mater derives its arteries from the anterio
 
and posterior spinal arteries, and the neural branches of the latera
 
spinal arteries.
 
 
 
Nerve-supply.—The nerves are derived from the sympathetic system
 
 
 
 
 
Structure. —The spinal pia mater consists of two layers—outer and innei
 
The outer layer consists of fibrous tissue, which is disposed for the most part i]
 
parallel longitudinal bundles. The inner layer consists of areolar tissue containing
 
a great many bloodvessels, and its outer and inner surfaces are covered by endcj
 
thelial cells. Between the two layers there are narrow cleft-like lymphati
 
spaces, which communicate with the subarachnoid space, and with lymphati
 
clefts around the arteries of the pia mater.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1415
 
 
 
 
 
The spinal pia mater differs from the cranial pia mater in being
 
icker and more adherent to the nervous matter. The greater thick:ss is due to the presence of the outer layer, the cranial pia mater
 
presenting the inner layer of the spinal pia mater.
 
 
 
Linea Splendens.—The pia mater at times presents a glistening
 
>pearance immediately in front of the ventral median fissure. This
 
ea is known as the linea splendens, and it extends along the entire
 
ngth of the cord and along the conus medullaris on to the filum
 
rminale.
 
 
 
Ligamentum denticulatum is a band of pia mater which extends
 
ong the spinal cord on each side opposite the corresponding lateral
 
>lumn. It lies between the ventral and dorsal roots of the spinal
 
irves, and extends from the margin of the foramen magnum to the
 
wer end of the cord. It lies within the subarachnoid space, and
 
 
 
 
 
Dura Mater
 
 
 
 
 
 
 
Fig. 862._Diagram of a Transverse Section of the Spinal Cord
 
 
 
and its Membranes.
 
 
 
 
 
A.M.F. Anterior Median Fissure, with
 
Process of Pia Mater
 
P.M.F. Posterior Median Sulcus
 
A.C. Anterior Column
 
L.C. Lateral Column
 
P.C. Posterior Column
 
 
 
 
 
A.R. Anterior Nerve-Root
 
P.R. Posterior Nerve-Root
 
G. Spinal Ganglion
 
S.P. Spinal Nerve
 
A.P.D. Anterior Primary Ramus
 
P.P.D. Posterior Primary Ramus
 
 
 
 
 
irtially divides that space into two compartments—ventral and
 
orsal
 
 
 
Internally it forms an uninterrupted band which is attached to
 
le pia mater along the lateral column of the cord. Laterally it is
 
enticulated. The denticulations (about twenty-one m number) carry
 
ith them sheaths from the arachnoid, and their pointed outer ends
 
re attached to the inner surface of the theca in the intervals between
 
ich pair of openings for the exit of the ventral and dorsal nerve-roots,
 
he topmost denticulation is at the foramen magnum, lying between
 
le eleventh nerve and the vertebral artery; the lowest is e ween
 
tie last thoracic and first lumbar nerves, at the first lumbar vertebral
 
 
 
iygl
 
 
 
The two ligamenta denticulata act as lateral supports to the spinal
 
°rd. ,. ,
 
 
 
Structure— Each ligamentum denticulatum consists of fibrous tissue, which
 
; continuous with the outer layer of the pia mater.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1416 A MANUAL OF ANATOMY
 
 
 
External Characters of the Spinal Cord. — The spinal cord, o
 
medulla spinalis, which is somewhat cylindrical, is that division o
 
the cerebro-spinal axis which is situated within the spinal canal. I
 
extends from the lower margin of the foramen magnum in the occipita
 
bone to about the level of the disc between the bodies of the firs
 
and second lumbar vertebrae, and it is about 18 inches in length
 
Superiorly it is continuous with the medulla oblongata, and inferiorh
 
it terminates in a tapering portion, called the conus medullaris. Fron
 
the lower end of this cone a slender, glistening thread, called tb
 
 
 
filum terminale, about io inche
 
long, is continued downward
 
between the bundles of lumbar
 
sacral, and coccygeal nerve
 
of either side, which constitut
 
the cauda equina, to be attache<
 
to the back of the first coccy
 
geal segment.
 
 
 
The spinal cord is of smalle
 
dimensions than the spina
 
canal, and is therefore relieve*
 
from pressure during the ordi
 
nary movements of the verte
 
bral column. It is surrounde*
 
by the three membranes alread;
 
described—the dura mater, th
 
archnoid membrane, and th
 
pia mater. Within its theca o
 
dura mater the cord is sus
 
pended by means of the liga
 
menta denticulata, and th
 
nerve - roots as they emerg
 
through the openings in th
 
theca.
 
 
 
The spinal cord varies ii
 
shape in different regions. L
 
the cervical region, as seen ii
 
transverse section, it is trans
 
versely oval, and is slights
 
flattened from before backwards. In the thoracic region it is almos
 
circular, but the transverse diameter exceeds the antero-posterior
 
In the lumbar region it is still more circular than in the thoraci
 
region.
 
 
 
The cord has two swellings, which are known as the cervical an*
 
lumbar enlargements, and are associated with the numerous larg<
 
nerve-trunks destined for the upper and lower limbs. The cervica
 
enlargement extends from near the upper end of the cord to the secon*
 
thoracic vertebra, and its breadth is greatest opposite the sixth cervica
 
vertebra. The lumbar enlargement, which is less conspicuous thai
 
 
 
 
 
 
 
Fig. 863. —Lumbar and Sacral Portions
 
of Spinal Canal, showing Lateral
 
View of Conus Medullaris, Filum
 
Terminale, and Theca (Testut).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1417
 
 
 
 
 
he cervical, extends from the level of the tenth thoracic vertebra
 
o the conus medullaris, and its breadth is greatest opposite the twelfth
 
horacic vertebra.
 
 
 
Filum Terminale.—This delicate glistening thread lies in the
 
nedian line between the lumbar, sacral, and coccygeal nerves of either
 
side, which constitute the cauda equina, and it extends from the apex
 
)f the conus medullaris to the back of the first coccygeal segment.
 
 
 
[t is about 10 inches in length. As low as the back of the body of
 
;he second or third sacral segment it is situated within the theca,
 
Dut at that level it pierces the theca,
 
from which it receives an investment,
 
md then passes to be attached to the
 
back of the first coccygeal segment, where
 
it blends with the periosteum. The intrathecal portion is known as the filum
 
terminale internum, and the extrathecal
 
portion as the filum terminale externum.
 
 
 
Structure. —The filum terminale internum in its upper half consists of pia
 
mater prolonged from the conus medullaris of the spinal cord. This encloses
 
grey matter, within which, over about
 
the upper third, there is a continuation
 
of the central canal of the cord. The
 
lower half consists chiefly of connective
 
tissue. The filum terminale externum is
 
a mere fibrous filament invested by a
 
prolongation of the theca which blends
 
with it. It is also composed of pia mater
 
prolonged downwards from the conus
 
medullaris, and reinforced by fibres derived from the lower portions of the ligamenta denticulata and linea splendens.
 
 
 
Its lower part is purely fibrous. Fig . 864 ._the terminal
 
 
 
Cauda EQuina.—This is situated witmn Part of the Spinal Cord,
 
 
 
the lower part of the theca. It consists and the Cauda Equina
 
of the roots of the lumbar, sacral, and ~
 
 
 
coccygeal nerves of each side, which are arranged m the form o a
 
leash, and the filum terminale lies in the median line between the
 
two nerve-leashes. On account of the high origins of the individual
 
nerves, relatively to the positions of the intervertebral foramina
 
through which they pass, the direction of the nerves is almost vertical
 
until they reach the level of their respective foramina o exi .
 
 
 
Fissures of the Spinal Cord.—The spinal cord, which is somewhat
 
flattened in front and behind, is incompletely divided into two symmetrical halves by two median formations, anterior and posterior.
 
The anterior median Assure extends into the cord for one-third of its
 
thickness from before backwards, and it contains a o c o le pia
 
 
 
 
 
 
 
 
 
_ Linea Splendens
 
 
 
 
 
Cauda Equina
 
Conus Medullaris
 
 
 
 
 
If
 
 
 
 
 
_Filum Terminale
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1418
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
mater. At the bottom of the fissure the transverse band of nervefibres, called the anterior white commissure , crosses between the two
 
halves of the cord. The posterior median septum is not an actual
 
fissure like the anterior, and does not contain a fold of the pia mater,
 
but is a septum of neuroglia, which extends into the cord for about
 
half its thickness from before backwards. The posterior grey commissure lies at the bottom of the septum. The anterior median fissure
 
is a definite depression, but it is not so deep as the posterior septum.
 
 
 
The posterior septum is marked on the surface by a median sulcus.
 
 
 
Each half of the cord presents a groove along the line of entrance
 
of the fasciculi of the posterior nerve-roots, called the postero-lateral
 
sulcus, but there is no similar groove along the line of emergence of
 
the fasciculi of the anterior nerve-roots, these being spread over an
 
area of some breadth. By means of the postero-lateral sulcus on the
 
one hand, and the area corresponding to the emergence of the fasciculi
 
of the anterior nerve-roots on the other, each half of the spinal cord is
 
divided superficially into three white columns—anterior, lateral, and
 
posterior.
 
 
 
The anterior white column is situated between the anterior median
 
fissure and the most lateral fasciculi of the anterior nerve-roots; the
 
lateral white column is the area between the most lateral fasciculi of
 
the anterior nerve-roots and the postero-lateral sulcus; and the posterior
 
white column lies between the postero-lateral sulcus and the posterior
 
median sulcus. Practically the anterior column represents the region
 
in front of the anterior nerve-roots, the lateral column the region between the anterior and posterior nerve-roots, and the posterior column
 
the region behind the posterior nerve-roots. According to some
 
authorities there are only two columns—namely, antero-lateral and
 
posterior, the former extending from the anterior median fissure to the
 
postero-lateral sulcus, and representing the combined anterior and
 
lateral columns.
 
 
 
In the cervical region the surface of each posterior white column
 
presents a slight groove which is situated nearer the posterior median
 
sulcus than the postero-lateral sulcus. This groove is called the
 
posterior intermediate or paramedian furrow . It contains a septum of
 
pia mater, and in this manner the posterior column of the cord is
 
marked off into two tracts. The medial and smaller tract is called
 
the fasciculus gracilis (postero-median column of Goll), and the lateral
 
and larger is called the fasciculus cuneatus (Burdach’s column, posterolateral column). These two columns extend throughout the cord, but it
 
is only above the level of the mid-thoracic region that they are separated
 
from each other by a septum of pia mater, known as the posterior
 
intermediate septum.
 
 
 
Origin of the Spinal Nerves.—There are thirty-one pairs of spinal
 
nerves, which arise from the sides of the spinal cord. They are arranged in five groups on either side as follows: cervical, eight in number;
 
thoracic, twelve ; lumbar, five ; sacral, five ; and coccygeal, one. Each
 
spinal nerve is attached superficially to the cord by two roots, anterior
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1419
 
 
 
 
 
nd posterior, the posterior root being the larger of the two. The
 
ortion of the cord from which each pair of spinal nerves arise is spoken
 
f as a segment of the cord. Each root is ensheathed by tubular probations of the coverings of the cord—namely, the pia mater, arachnid, and dura mater, in this order from within outwards—and these
 
heaths ultimately blend with the perineurium. The roots are separated
 
rom each other by the lateral column of the cord and the ligamentum
 
enticulatum, and they pass through separate openings in the theca of
 
;ura mater.
 
 
 
The anterior roots are composed of efferent or motor fibres, and their
 
asciculi emerge from the cord in an irregular manner, being spread
 
ver an area corresponding in breadth to the caput of the anterior
 
 
 
A
 
 
 
2
 
 
 
 
 
 
 
?IG. 865.—Two Segments of the Spinal Cord, showing the Attachments
 
of the Anterior and Posterior Nerve-Roots, and the Spinal Ganglia.
 
 
 
A, superior view; B, anterior view.
 
 
 
1, 1. Anterior Median Fissure 5 > 5 - Spinal Ganglion
 
 
 
2, 2. Posterior Median Sulcus 6, 6. Spinal Nerve
 
 
 
a, a. Anterior or Motor Nerve-Root 7 , 7 - Anterior Primary Ramus
 
 
 
4, 4. Posterior or Sensory Nerve-Root 8, 8. Posterior Primary Ramus
 
 
 
9, 9. Medial and Lateral Branches of Posterior Primary Ramus
 
 
 
horn of the grey matter in the interior. The posterior roots are composed of afferent or sensory fibres, and their fasciculi enter the cord
 
in a straight line along the course of the postero-lateral sulcus. Each
 
posterior root presents an oval swelling, called the spinal ganglion.
 
These ganglia are for the most part situated in the intervertebral
 
foramina, and immediately beyond each ganglion the anterior and
 
posterior roots unite to form a spinal nerve, which is necessarily a
 
mixed nerve, inasmuch as it is composed of afferent and efferent fibres.
 
 
 
Each spinal nerve breaks up into an anterior and a posterior primary
 
yamus
 
 
 
The upper cervical nerve-roots are short, and pass almost horizontally outwards. The succeeding nerve-roots, however, gradually
 
increase in length, and incline downwards as they pass outwards,
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1420
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
This downward inclination goes on increasing until it becomes almost
 
vertical in the case of the lumbar, sacral, and coccygeal nerves, which
 
constitute the cauda equina. From this disposition it follows that
 
in the majority of cases the superficial origins of the spinal nerves are
 
on a higher level than the intervertebral foramina through which they
 
emerge from the spinal canal.
 
 
 
Relation of the Spines of Vertebrae to the Bodies and to the Origins of the
 
Nerves. —In the case of the cervical and the eleventh and twelfth thoracic vertebra
 
the extremities of the spinous processes correspond to the lower margins of
 
the bodies of the respective vertebrae. In the case of the thoracic vertebra,
 
from the first to the tenth inclusive, the extremity of each spinous process corresponds to some part of the body immediately below. In the case of the lumbar
 
vertebrae the extremity of each spinous process corresponds to the centre of the
 
body of its own vertebra.
 
 
 
Each cervical spinous process is nearly opposite the lower fasciculi of the
 
roots of the nerve below. The spinous process of the seventh cervical vertebra
 
(vertebra prominens) is opposite the roots of the first thoracic nerve. From
 
the third to the tenth thoracic vertebrae the spinous processes correspond to
 
the second root below. The eleventh thoracic spine corresponds to the first and
 
second lumbar nerves. The twelfth thoracic spine corresponds to the third,
 
fourth, and fifth lumbar nerves. The first lumbar spine corresponds to the
 
first, second, and third sacral nerves. (Gowers, from an original investigation.)
 
 
 
 
 
Mode of distinguishing the Anterior and Posterior Surfaces of the
 
Spinal Cord.—These surfaces may be recognized by attending to the
 
following points:
 
 
 
 
 
Anterior Surface.
 
 
 
1. Linea splendens in median line,
 
 
 
especially in lower part.
 
 
 
2. Anterior spinal artery in
 
 
 
median line.
 
 
 
3. Fasciculi of anterior nerve
 
roots spread over a wide
 
area.
 
 
 
4. Presence of an anterior median
 
 
 
sulcus which can be opened.
 
 
 
 
 
Posterior Surface.
 
 
 
1. Ganglion on each posterior nerve
 
root.
 
 
 
2. Arterial anastomotic chain behind and
 
 
 
in front of the posterior nerve-roots.
 
 
 
3. Fasciculi of posterior nerve-roots lie
 
 
 
in a straight line, and enter through
 
postero-lateral sulcus.
 
 
 
4. Presence of a posterior median sulcus
 
 
 
which cannot be opened.
 
 
 
5. Presence of gracile and cuneate fasci
 
culi in upper part.
 
 
 
 
 
Internal Structure of the Spinal Cord.—The spinal cord, as seen in
 
transverse section, consists of a central portion composed of grey matter,
 
and an external portion composed of white matter.
 
 
 
Grey Matter.—This is arranged in the form of two irregular crescents,
 
the concavities of which are directed outwards, and the convexities
 
inwards, the latter being connected across the middle line by the
 
grey commissure. The arrangement has been likened to the letter )-(.
 
The grey commissure lies at the bottom of the posterior median sulcus,
 
and presents about its centre the minute opening of the central canal
 
of the cord. The part of the commissure in front of this canal is
 
known as the anterior grey commissure, and the part behind as the
 
posterior grey commissure. In front of the anterior grey commissure
 
there is a transverse band of white matter, called the anterior white
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1421
 
 
 
 
 
immissure, which lies at the bottom of the anterior median fissure,
 
ach crescent of grey matter consists of two horns, anterior and
 
osterior, the former being in front of, and the latter behind, the grey
 
mnmissure. The anterior horn is broad and blunt, and it stops short
 
f the surface of the cord, being separated from the surface by white
 
latter which is traversed by the fasciculi of the anterior nerve-roots,
 
he blunt extremity of the anterior horn is called the caput cornu, and
 
le portion adjoining the grey commissure, which is slightly constricted,
 
; called the cervix cornu. The posterior horn is for the most part
 
mg, narrow, and tapering, and its pointed extremity almost reaches
 
tie surface of the cord at the bottom of the postero-lateral sulcus,
 
'his pointed extremity is called the apex cornu, and it contains a transient substance, known as the substantia gelatinosa (of Rolando),
 
diich forms the cap for the caput cornu posterioris. It contains a
 
 
 
 
 
Central Canal
 
 
 
 
 
 
 
?i G . 866._ Transverse Section of the Spinal Cord in the Upper Thoracic
 
 
 
Region, showing the Arrangement of the Grey Matter and Cells
 
(Semi-diagrammatic) (after Poirier).
 
 
 
small amount of neuroglia, and numerous nerve-cells. The portion
 
idjoining the grey commissure, which is slightly constricted, is called
 
the cervix cornu, and the portion contiguous to the cervix, w 11c is
 
slightly enlarged, is called the caput cornu. The part between the
 
 
 
two cornua is called the body. ' ,
 
 
 
About the centre of the concavity of the body crescent the grey
 
 
 
matter projects into the lateral column in the form of processes arranged
 
in a reticular manner and enclosing white matter. This network is
 
sailed the processus reticularis, and it is most conspicuous m the
 
cervical region. In the thoracic region, more particular y in 1 s uppei
 
part, the grey matter of each crescent forms a triangular projection
 
which extends laterally for a short distance immediately m front of
 
the processus reticularis, and adjacent to the junction o e an erior
 
:ornu with the grey commissure. This projection is known as the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1422
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
lateral horn. When followed into the lower cervical and into the
 
lumbar regions it blends with the anterior horn, the thickness of which
 
it increases, but it is again present above the level of the fourth cervical
 
vertebra.
 
 
 
The grey matter has been described, so far, as it would be seen on
 
looking at transverse sections through the cord; under such conditions
 
the use of the term ' horn ’ or ' cornu * is quite appropriate. As it
 
exists in the complete cord, however, the grey matter is in the form
 
of a continuous column , and in considering it in such a way it should
 
be described as possessing anterior, posterior, and lateral ' columns,’
 
rather than ‘ horns.’
 
 
 
The grey matter varies in amount in different parts of the cord.
 
It is present in largest quantity in the lumbar enlargement, where
 
the large nerve-trunks for the lower limbs arise, and next to this in
 
the cervical enlargement, where the large nerve-trunks for the upper
 
limbs arise.
 
 
 
The horns of the crescents of grey matter vary in shape, as seen
 
on section, in different regions. In the cervical region the anterior
 
 
 
 
 
A
 
 
 
 
 
 
 
Fig. 867. —Transverse Sections of the Spinal Cord in Different
 
 
 
Regions.
 
 
 
A, cervical region; B, mid-thoracic region; C, lumbar region; D, conus
 
 
 
medullaris.
 
 
 
horns are short, broad, and blunt, and the posterior horns are long,
 
narrow, and pointed. In the thoracic region both horns are narrow,
 
though the posterior is more so than the anterior. In the lumbar
 
region both are broad, though the anterior is more so than the posterior.
 
These differences render sections of the spinal cord in the cervical,
 
thoracic, and lumbar regions easily recognizable. As stated, the lateral
 
horn is also a characteristic of the cord in the thoracic region, more
 
particularly in its upper part.
 
 
 
Central Canal.—This minute canal is situated about the centre of
 
the grey commissure, and extends throughout the entire length of the
 
spinal cord. Superiorly it is continued into the lower half of the
 
medulla oblongata, and it opens into the lower part of the fourth
 
ventricle at the calamus scriptorius. Interiorly, near the apex of the
 
conus medullaris it becomes enlarged, and assumes the shape of an
 
inverted ±. This enlargement is known as the ventriculus terminalis.
 
From this point it is prolonged for some distance into the filum terminale,
 
and it ends in a closed extremity. In the cervical and thoracic regions
 
the central canal is nearer the anterior surface of the cord than the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
i 4 2 3
 
 
 
 
 
sterior, but in the lumbar region it occupies the centre. In the
 
aus medullaris it is near the posterior surface.
 
 
 
The canal is lined with ciliated columnar epithelium, the columnar
 
Is being known as ependymal cells.
 
 
 
The central canal represents the lumen of the neural tube of ectoderm from
 
ich the spinal cord is developed.
 
 
 
White Matter of the Spinal Cord.—The white matter forms the
 
ter part of the cord, and is arranged in three columns—anterior,
 
teral, and posterior. The anterior column is situated between the
 
iterior median fissure and the anterior horn of grey matter, and
 
tends as far as the most lateral fasciculi of the anterior nerve-roots,
 
therefore includes the superficial coating of the anterior horn, where
 
is traversed, over an area of some breadth, by the scattered fasciculi
 
the anterior nerve-roots. The lateral column is situated between the
 
iterior and posterior horns of grey matter, in the concavity of the
 
escent. Its superficial limits are the most lateral fasciculi of the
 
iterior nerve-roots and the fasciculi of the posterior nerve-roots at
 
e postero-lateral sulcus. The posterior column is situated between
 
e posterior median sulcus and the posterior horn of grey matter, its
 
perficial limit being the fasciculi of the posterior nerve-roots at the
 
>stero-lateral sulcus.
 
 
 
The white matter increases in quantity from below upwards, and
 
pta of pia mater and neuroglia fibres pass into it at various points.
 
 
 
 
 
Jhief Distinguishing Characters of the Spinal Cord in Different Regions, as
 
 
 
seen in Transverse Sections.
 
 
 
 
 
Cervical Region.
 
 
 
Transversely oval.
 
 
 
Anterior Horn, short,
 
broad, and blunt.
 
 
 
Posterior Horn, long,
 
narrow, and tapering.
 
 
 
Formatio Reticularis, well marked.
 
 
 
Lateral Horn, merged
 
into anterior, except above fourth
 
cervical vertebra.
 
 
 
White Matter, large
 
in amount.
 
 
 
 
 
Central Canal,
 
nearer the ventral
 
than the dorsal
 
surface.
 
 
 
Postero - intermediate Sulcus and
 
Septum of pia
 
mater, well
 
marked.
 
 
 
 
 
Thoracic Region.
 
 
 
1. Circular.
 
 
 
2. Anterior and Posterior
 
 
 
Horns, both narrow,
 
posterior more so
 
than anterior.
 
 
 
3. Formatio Reticularis,
 
 
 
not very distinct.
 
 
 
4. Lateral Horn, con
 
spicuous, especially
 
in upper part
 
 
 
5. White Matter, less in
 
 
 
amount, but large
 
in proportion to
 
Grey Matter.
 
 
 
6. Central Canal, nearer
 
 
 
the ventral than the
 
dorsal surface.
 
 
 
7. Postero - intermediate
 
 
 
Sulcus, absent, but
 
Septum of pia mater
 
recognizable.
 
 
 
 
 
Lumbar Region.
 
 
 
1. Almost circular.
 
 
 
2. Anterior and Posterior
 
 
 
Horns, both broad,
 
anterior more so
 
than posterior.
 
 
 
3. Formatio Reticularis,
 
 
 
absent.
 
 
 
4. Lateral Horn, merged
 
 
 
into anterior.
 
 
 
 
 
5. White Matter, small
 
 
 
in amount, and Grey
 
Matter, large.
 
 
 
6. Central Canal, in the
 
 
 
centre.
 
 
 
 
 
7. Postero - intermediate
 
Sulcus and Septum
 
of pia mater, absent.
 
 
 
 
 
I 4 2 4
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Minute Structure of the Spinal Cord—Grey Matter.—The grey
 
matter consists of nerve-cells, nerve-fibres, and neuroglia, and is very
 
vascular.
 
 
 
The nerve-cells are present in great numbers, and are multipolar.
 
Each cell sends off at various points several protoplasmic processes,
 
one of which becomes the axis-cylinder of a nerve-fibre, and is called
 
the axis-cylinder process, or axon. The other processes are known as
 
the protoplasmic processes {of Deiters), or dendrites, and, after successive
 
branchings, they terminate in free extremities. There are no anastomoses between the dendrites of the same cell, nor between those of
 
contiguous cells. A multipolar nerve-cell, with its axon and dendrites,
 
constitutes a neuron. The multipolar cells form longitudinal columns
 
of various lengths, and, as seen in transverse sections of the cord,
 
they are arranged in groups which occupy particular regions. These
 
 
 
Central Canal
 
 
 
 
 
 
 
Fig. 868.— Transverse Section of the Spinal Cord in the Upper Thoracic
 
Region, showing the Arrangement of the Grey Matter and Cells
 
(Semi-diagrammatic) (after Poirier).
 
 
 
cell-columns or groups are three in number—namely, anterior or
 
ventral, in the anterior horn of grey matter; lateral, in the lateral
 
horn of grey matter; and posterior, constituting the thoracic nucleus
 
(or posterior vesicular column of Lockhart Clarke), and being very
 
conspicuous in the medial portion of the cervix of the posterior grey
 
horn in the thoracic region. Besides these main columns or groups,
 
other nerve-cells are present, which are scattered irregularly throughout
 
the other portions of the grey matter.
 
 
 
The anterior or ventral cell-column is situated, as stated, in the
 
anterior horn of grey matter, and extends throughout the whole length
 
of the spinal cord. Its cells are of large size and very conspicuous,
 
and their axons, which are at first non-medullated, become medullated,
 
and then constitute the fasciculi which emerge to form the anterior
 
nerve-roots. These cells are therefore the sources from which the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
*4 25
 
 
 
 
 
Trent or motor nerve-fibres proceed, and the ventral column is
 
nsequently spoken of as the motor column. The ventral or motor
 
11 s of this column are arranged in two groups, medial and lateral,
 
re medial group occupies the medial part of the anterior grey horn,
 
id the lateral group is situated in its outer part. In the cervical and
 
mbar enlargements of the cord the cells of the lateral group are very
 
imerous, and are arranged in two sub-groups, ventro-lateral and
 
)rso-lateral.
 
 
 
The intermedio-lateral cell-column is situated, as stated, in the
 
teral horn of grey matter, and the cells constitute a column known
 
 
 
; the intermedio-lateral nucleus.
 
 
 
The thoracic cell-column is situated in the medial part of the
 
:rvix of the dorsal cornu of grey matter. This extends throughout
 
le entire thoracic region of the cord, and for a short distance into
 
le cervical and lumbar enlargements. The cells make an elongated
 
jcleus (often termed Clarke’s column), and are of large size. This
 
)lumn exists chiefly in the thoracic portion of the cord, whence the
 
ime thoracic nucleus.
 
 
 
The cells of the grey matter differ as regards their axons, some having short,
 
id others long, axons.
 
 
 
The cells with short axons have their axons confined to the grey matter,
 
which they ramify not far from the parent-cells. They serve to bring contiguis cells into relation with one another.
 
 
 
The cells with long axons are partly root-cells and partly association-cells^
 
id their axons travel for some distance from the parent-cells. The axons of
 
le root-cells leave the cord in the fibres of the ventral or motor nerve-roots,
 
he axons of the association-cells constitute association-fibres, which are disused in two ways: (1) Some enter the white matter of the same side of the
 
>rd, in which they divide into ascending and descending branches. Eventually
 
iey re-enter the grey matter, and terminate in arborizations at some distance
 
om the parent-cells. (2) Other association-fibres cross to the opposite side
 
1 the ventral or white commissure. Some of these end in arborizations around
 
le cells of the grey crescent, whilst others enter the white matter, in which
 
ley are disposed as on the side from which they have crossed.
 
 
 
Destination of Axons of Cells of Grey Matter.
 
 
 
Cells of Ventral Horn. —(1) Many axons become the axis-cylinder processes
 
f the efferent fibres of the ventral nerve-roots. (2) Other axons constitute
 
ssociation-fibres, which cross to the opposite side in the ventral 01 white comlissure. After crossing, some end in arborizations around the cells of the
 
entral horn * others enter the white matter; and a few are regarded by some
 
uthorities as entering the ventral nerve-roots of the side to which they have
 
rossed
 
 
 
Cells Of Lateral Horn.—The axons of the cells of the intermedio-lateral nucleus
 
ass to the efferent fibres of the ventral nerve-roots, and they are regarded as
 
irnishing the white rami communicantes of the sympathetic system.
 
 
 
Cells Of Dorsal Horn. —The axons of the cells of the dorsal horn have various
 
irections; (1) Some pass to the ventral horn and ventral 01 white commissure.
 
>) The axons of the cells of the thoracic nucleus pass to the lateral column, and
 
re usually regarded as entering the dorsal cerebellar and ventro-lateral cereellar tracts. (3) The axons of the cells of the substantia gelatmosa pass partly
 
3 the lateral column, adjacent to the dorsal horn, where they divide into ascenc ig and descending branches, and partly into the posterior marginal bun e o
 
 
 
90
 
 
 
 
 
1426
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Lissauer. (4) The axons of other cells in the lateral part of the cervix of tb
 
dorsal horn pass to the lateral and ventral horns, the ventral or white commissure
 
and the lateral column. (5) The axons of the cells of the caput cornu posteriori
 
pass to the lateral column of the same side, and a few are regarded as passinj
 
to the opposite side in the ventral or white commissure.
 
 
 
Dorsal or Grey Commissure. —This commissure lies at the bottoir
 
of the dorsal median septum. It consists of (1) grey matter, con
 
taining a few small nerve-cells, and (2) medullated nerve-fibres. Thes(
 
fibres pass across from one side to the other, and later on diverge ir
 
each grey crescent. They serve as association fibres which bring th(
 
cells of opposite sides into relation with one another. This commissun
 
contains the central canal of the cord, which for the most part is nearei
 
the ventral portion of the commissure than the dorsal. The part o:
 
the commissure surrounding the central canal is called the substantia
 
gelatinosa centralis. It consists of neuroglia, a few nerve-cells, anc
 
nerve-fibres; and it is invaded by processes derived from the deep end. c
 
of the ciliated columnar epithelial cells which line the central canal.
 
 
 
Summary of the Gelatinous Substances of the Grey Matter. — These are
 
 
 
(1) The substantia gelatinosa, which forms a cap for the caput cornu posterioris :
 
 
 
(2) the substantia gelatinosa centralis, which surrounds the central canal ©f the
 
cord; and (3) the substantia gelatinosa externa, which forms the glial sheath oj
 
the cord beneath the pia mater.
 
 
 
White Matter. —The white matter of the cord consists of longitudinal medullated nerve-fibres, traversed by septa of the pia mater,
 
and embedded in neuroglia. The fibres have no primitive sheath or
 
neurilemma.
 
 
 
Ventral or White Commissure. —This commissure lies at the bottom
 
of the ventral median fissure, and it is separated from the central canal
 
of the cord by a part of the dorsal or grey commissure. It consists ol
 
medullated nerve-fibres, destitute of a neurilemma, some of which
 
pass transversely, but most of them decussate, entering the commissure ventrally on one side, and leaving it dorsally on the opposite
 
side. The fibres, after crossing, enter the grey crescent and the ventral
 
column. They are derived from (1) the anterior cerebro-spinal tract,
 
(2) the processes of root-cells and of association cells, and (3) the fibres
 
of the spino-thalamic tract, to be presently described.
 
 
 
Fibres of Roots of Spinal Nerves—Ventral or Anterior NerveRoots. —The fibres of the ventral nerve-roots arise within the cord
 
from several sources. (1) Many of them are axons of the medial cells
 
of the ventral horn of grey matter of the same side. (2) Some are axons
 
of the lateral cells of the ventral horn. (3) Others are axons of the
 
cells of the thoracic nucleus of the same side. (4) A few are axons
 
of cells in the dorsal horn of grey matter of the same side. (5) A few
 
are regarded as being axons of the medial cells of the ventral and intermediate grey matter of the opposite side , which cross in the ventral
 
or white commissure. All the axons receive their medullary sheaths
 
near the parent cells, and they form funiculi, which leave the white
 
matter of the ventral column over an area corresponding to the caput
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1427
 
 
 
 
 
the ventral horn of grey matter, after which each fibre acquires its
 
imitive sheath or neurilemma.
 
 
 
Most of the axons of the fibres of the ventral nerve-roots belong to the
 
ntral (motor) cells of the ventral horn of grey matter of the same side.
 
 
 
Dorsal or Posterior Nerve-Roots.—The fibres of the dorsal nerveots arise from the unipolar (orginally bipolar) cells of the spinal
 
nglia. The single pole or process of each of these cells is T-shaped,
 
le half of the horizontal limb of the T is central, and enters the cord
 
 
 
 
 
 
 
 
 
' IG . 869.— Course of Nerve-Fibres in the Spinal Cord (from Halliburton’s
 
* Handbook of Physiology ’ (after Schafer).
 
 
 
 
 
P. Cerebro-spinal Tract
 
1, 2, 3, 4. Anterior Cornual Cells
 
K, A, A, A. Axons of Anterior Cornual Cells
 
M. Muscular Fibre
 
 
 
G. Unipolar Cell of a Spinal Ganglion, giving
 
Origin to a Fibre of a Posterior NerveRoot
 
 
 
B. Peripheral Branch of Fibre
 
S. Skin . .
 
 
 
(lowerC) Central Branch of Fibre, passing into the
 
Spinal Cord
 
 
 
. Descending Branch of Fibre in the Spinal Cord
 
 
 
 
 
D. Ascending Branch of Fibre in the Spinal Cord
 
Pi, P2. Posterior Cornual Cells
 
 
 
C (upper C). Cell of Clarke’s Column or Thoracic
 
 
 
Nucleus .
 
 
 
5. Collateral, passing directly to arborize around an
 
 
 
Anterior Cornual Cell (2). >
 
 
 
6. Collateral, with an Intermediate Cell-Station in a
 
 
 
Posterior Cornual Cell (P 2 ).
 
 
 
7. Collateral, arborizing around a Cell ot Clarke s
 
 
 
Column (upper C). ,
 
 
 
8. Continuation of Main Ascending Branch of Fibre.
 
 
 
 
 
the dorso-lateral sulcus between the dorsal and lateral coiumns of
 
ilte matter. The other half of the horizontal limb is peripheral, and
 
 
 
sses outwards in the course of the nerve. • ol K 11 n f
 
 
 
Within the cord a few lateral fibres enter the marginal bundle
 
3sauer, and the dorsal horn of grey matter, but most of them pass
 
-o th e poslero-lateral column (Burdach) close to the dorsal horn of
 
;y matter. Within this column the fibres divide into ^ branches
 
lending and descending. The descending branches, after a short
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1428
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
course, enter the dorsal horn. These descending fibres are usualh
 
regarded as forming the ‘ comma tract.’ The ascending branches
 
are longer than the descending, and, at various levels, they also enter
 
the dorsal horn. The ascending branches of the fibres of the dorsal
 
roots of the lower spinal nerves enter the postero-medial column.
 
 
 
The ascending and descending branches give off numerous collateral
 
fibrils, which enter the dorsal grey column. These collaterals have
 
the following destinations: (1) The dorsal horn of the same side, and
 
that of the opposite side through the dorsal or grey commissure; and
 
(2) the ventral and lateral horns of the same side. In each case they
 
 
 
come into close relation with the corresponding nerve-cells_ e.g., the
 
 
 
cells of the dorsal horn, including the thoracic nucleus, the ventral or
 
motor cells of the ventral horn, and the cells of the thoracic nucleus
 
in the lateral horn.
 
 
 
 
 
Sensory Fibres entering Fasciculus Cuneatus (Burdach)
 
Cells of Posterior Column and Thoracic Nucleus ' Posterior Ro<
 
 
 
 
 
 
 
Spinal Ganglia. — these are situated on the posterior roots of the
 
spinal nerves in the intervertebral foramina, and outside the theca,
 
though invested by a prolongation from it. Each ganglion is oval,
 
and consists of unipolar nerve-cells. The single pole of each cell
 
divides into two processes, one of which is centripetal and forms part
 
of the posterior nerve-root, whilst the other is centrifugal and passes
 
into the spinal nerve. The pole and its inward and outward processes
 
resemble the letter T. In early life the cells are bipolar.
 
 
 
The fibres of the posterior nerve-roots have their deep origins in
 
the unipolar cells of the spinal ganglia, and they grow into the spinal
 
cord. On the other hand, the fibres of the anterior nerve-roots have
 
their deep origins within the spinal cord, where they arise as the axons
 
of the multipolar nerve-cells of the anterior column of grey matter, and
 
they grow outwards.
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1429
 
 
 
 
 
Tracts of the Spinal Cord.
 
 
 
Posterior Column. —The tracts of this column are ascending and
 
xending, and they are as follows:
 
 
 
Ascending Tracts. Descending Tracts
 
 
 
Fasciculus gracilis (Fig. 871, 1). Semilunar (comma) tract (Fig. 871, 9).
 
Fasc. cuneatus (Fig. 871, 2). Septo-marginal bundle (Fig. 871, 10).
 
 
 
Postero-lateral tract (of Lissauer)
 
 
 
(Fig. 871, 3).
 
 
 
Lissauer’s tract also belongs to the lateral column.
 
 
 
 
 
 
 
19
 
 
 
Descending
 
 
 
 
 
Ascending.
 
 
 
 
 
; F IG . 871.— The Tracts of the Spinal Cord.
 
 
 
 
 
Ascending.
 
 
 
Fasciculus gracilis (Goll’s column).
 
 
 
:. Fasciculus cuneatus (Burdach’s column).
 
 
 
Fasciculus postero-lateralis (Lissauer’s tract). _
 
 
 
|.. Posterior spino-cerebellar fasciculus (Flechsig’s
 
tract).
 
 
 
5. Anterior spino-cerebellar fasciculus (Gower’s
 
tract).
 
 
 
5 . Lateral spino-thalamic tract.
 
 
 
7. Anterior spino-thalamic tract.
 
 
 
1 . Intersegmental tract (fasciculus proprius: ground
 
bundle).
 
 
 
 
 
Descending.
 
 
 
9. Semilunar (or comma) tract.
 
 
 
10. Septo-marginal bundle.
 
 
 
n. Lateral cerebro-spinal fasciculus (crossed pyramidal tract).
 
 
 
12. Anterior cerebro-spinal fasciculus (direct pyra
 
midal tract).
 
 
 
13. Lateral intersegmental tract.
 
 
 
14. Anterior intersegmental tract.
 
 
 
15. Sulco-marginal tract.
 
 
 
16. Rubro-spinal tract (Monakow’s bundle).
 
 
 
17. Tecto-spinal tract.
 
 
 
18. Olivo-spinal tract (Helweg’s tract).
 
 
 
19. Vestibulo-spinal tract.
 
 
 
 
 
Ascending Tracts. —The fasciculus gracilis (tract of Goll) is situated
 
ose to the posterior median septum. Its fibres are derived from the
 
orsal roots of the coccygeal, sacral, lumbar, and lowei thoracic nerves,
 
hey are at first contained in the cuneate tract, but as they ascend
 
ley are gradually displaced medially, and so foim a special tract,
 
he fibres terminate superiorly in connection with the cells of the
 
 
 
ucleus gracilis of the medulla oblongata.
 
 
 
The fasciculus cuneatus (tract of Burdach) is situated on the lateial
 
ide of the tract of Goll next to the dorsal horn of grey mattei.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1430
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Above the mid-thoracic region it is separated from Goll’s tract by
 
the dorsal intermediate or paramedian furrow and a septum of pia
 
mater. Its fibres are derived from the dorsal nerve-roots. Above
 
the mid-thoracic region they are derived from the dorsal roots of the
 
upper thoracic and cervical spinal nerves, and these fibres terminate
 
superiorly in connection with the cells of the nucleus cuneatus of the
 
medulla oblongata. Below the mid-thoracic region the fibres are
 
derived from the lower dorsal nerve-roots, and these, being displaced
 
inwards into the gracile tract, terminate in connection with the cells
 
of the nucleus gracilis.
 
 
 
The postero-lateral fasciculus (Lissauer’s tract) is close to the outer
 
surface of the cord. It embraces the contiguous parts of the posterior
 
and lateral columns, and occupies the region of the dorso-lateral sulcus
 
where the funiculi of the dorsal nerve-roots enter the cord. It lies
 
between the substantia gelatinosa and the surface of the cord. Its
 
fibres are derived from the dorsal nerve-roots, and they ascend close
 
to the substantia gelatinosa , in which they terminate at different
 
levels.
 
 
 
Descending Tract.—The semilunar tract (comma) is situated in the
 
cuneate fasciculus. Its fibres are usually regarded as being derived
 
from the descending branches of the fibres of the dorsal nerve-roots,
 
in which case they are exogenous. The other view, however, is that
 
the fibres are intrinsic or endogenous, and spring from the cells of the
 
dorsal cornu of grey matter.
 
 
 
Antero-lateral Column,—1 he tracts of this column are arranged into
 
descending and ascending, and are as follows:
 
 
 
 
 
Descending Tracts.
 
 
 
1. Lateral cerebro-spinal (crossed pyra
 
midal) tract (Fig. 871, 11).
 
 
 
2. Anterior cerebro-spinal (direct pyra
 
midal) tract (Fig. 871, 12).
 
 
 
3. Intersegmental tract (Fig. 871, 13 and
 
 
 
14).
 
 
 
4. Rubrospinal tract (Fig. 871, 16).
 
 
 
5. Vestibulo-spinal tract (Fig. 871, 19).
 
 
 
6. Olivo-spinal tract (Fig. 871, 18).
 
 
 
7. Tecto-spinal tract (Fig. 871, 17).
 
 
 
 
 
Ascending Tracts.
 
 
 
1. Dorsal spino-cerebellar tract
 
 
 
(Fig. 871, 4).
 
 
 
2. Ventral spino-cerebellar tract
 
 
 
(Fig. 871, 5).
 
 
 
3. Anterior spino-thalamic tract
 
 
 
(Fig. 871, 7).
 
 
 
4. Lateral spino-thalamic tract
 
 
 
(Fig. 871, 6).
 
 
 
5. Spino-tectal tract (Fig. 871, 6).
 
 
 
 
 
Descending Tracts.—The crossed pyramidal or lateral cerebro-spinal
 
tract (fasciculus spinalis lateralis, Fig. 871, 11) is a long descending
 
tract of large size, which is situated deeply in the dorsal part of the
 
lateral column directly in front of the dorsal cornu of grey matter. It
 
is separated from the outer surface of the cord by the dorsal spinocerebellar (or direct cerebellar) tract. It diminishes in size as it
 
descends, and in the lumbar region it becomes superficial. At about
 
the level of the third sacral nerve it ends. The fibres of this tract have
 
their origin in the pyramidal cells of the motor area of the cortex of the
 
cerebral hemisphere of the opposite side. From this origin they descend
 
through (1) the internal capsule of the corpus striatum, (2) the crus
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
i43i
 
 
 
 
 
srebri, and (3) the pons. On leaving the pons they enter the pyramid
 
f the medulla oblongata on the side from which they have arisen,
 
t the lower part of the pyramid they cross to the opposite side and
 
ike up their position deeply in the dorsal part of the lateral column
 
f the spinal cord. The fibres of the crossed pyramidal tract of one
 
de therefore come from the cerebral hemisphere of the opposite side,
 
nd they form the inner and larger part of the pyramid of the medulla
 
blongata, also of the opposite side. As this tract descends, fibres
 
;ave it in each segment of the cord. These fibres enter the ventral
 
orn of grey matter, and end in close relation with the ventral or
 
lotor cells, the axons of many of which form the axis-cylinder prossses of the fibres of the ventral or motor nerve-roots.
 
 
 
The direct pyramidal or anterior cerebro-spinal tract is of small size,
 
nd is situated in the anterior column, where it lies close to the ventral
 
ledian fissure. It diminishes in size as it descends, and usually
 
srminates about the centre of the thoracic region, but fibres have been
 
raced as low as the fourth sacral nerve. The fibres of this tract, like
 
lose of the crossed pyramidal tract, have their origin in the pyramidal
 
ills of the motor area of the cortex of the cerebral hemisphere, but in
 
his case of the same side. The fibres of the direct pyramidal tract of
 
ne side therefore come from the cerebral hemisphere of the same side,
 
hey pursue a similar downward path as low as the pyramid of the
 
ledulla oblongata of the same side, of which they form the smaller
 
art. They take no part, however, in the decussation of the pyramids,
 
s do the fibres of the crossed pyramidal tract. Their course is directly
 
ownwards into the corresponding half of the spinal cord, where most
 
fthem take up their position in the anterior column close to the ventral
 
ledian fissure. The fibres of the direct pyramidal tract, though they
 
ike no part in the decussation of the pyramids, cross to the opposite
 
ide at regular intervals as they descend in the anterior column of
 
tie cord. The crossing takes place in the ventral or white commissure,
 
nd, having entered the ventral horn of grey matter of the opposite
 
ide, the fibres end, like those of the crossed pyramidal tract of that
 
ide, in close relation with the ventral or motor cells, the axons of
 
lany of which pass to the ventral or motor nerve-roots.
 
 
 
Most of the pyramidal fibres therefore cross from the side on which
 
hey arise to the opposite side. In the case of the crossed pyramidal
 
ract the crossing takes place in the lower part of the medulla obmgata. In the case of the direct pyramidal tract the crossing takes
 
lace in the ventral median fissure of the spinal cord along the course
 
f the tract.
 
 
 
The ground-bundle or intersegmental tracts (fasciculus proprius
 
nterior, Fig. 871, 14; lateralis, Fig. 871, 13; and posterior , Fig. 871, 8)
 
ontain association fibres linking together various parts of the cord,
 
he fasciculus proprius anterior is continued up into the medulla as
 
he posterior longitudinal bundle, but the ground-bundles, as a whole,
 
re regarded as descending tracts.
 
 
 
The vestibulo-spinal tract (fasciculus vestibulo-spinalis, Fig. 871,
 
 
 
 
 
1432
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
ig) is situated in the anterior column, where it lies superficially. It
 
forms a communication between the vestibular structures, through
 
Defiers’ nucleus, with the motor cells of the cord.
 
 
 
The prepyramidal or rubro-spinal tract (Fig. 871, 16) is situated
 
in the lateral column on the ventral aspect of the crossed pyramidal
 
tract. Its fibres are chiefly derived from the red nucleus of the tegmentum or dorsal part of the crus cerebri of the opposite side, and they
 
are regarded as terminating in the dorsal part of the ventral grey
 
matter.
 
 
 
The tecto-spinal tract (fasciculus tecto-spinalis , Fig. 871, 17) runs
 
from the superior corpus quadrigeminum of the opposite side to the
 
motor cells, and lies in front of the rubro-spinal tract.
 
 
 
The bulbo-spinal or olivo-spinal tract, or bundle of Helweg (Fig. 871)
 
18), is confined to the cervical region of the cord, and is triangular.
 
Its fibres are regarded as arising in the medulla oblongata behind the
 
olive, but their mode of termination is not known. They lie near the
 
surface of the cord external to the anterior nerve-roots.
 
 
 
Ascending Tracts.—The dorsal spino-cerebellar tract, or direct
 
cerebellar tract (of Flechsig) (Fig. 871, 4), is situated in the lateral
 
column. It lies in front of the dorso-lateral sulcus, between the
 
crossed pyramidal tract and the outer surface of the cord.. It commences in the lower part of the thoracic region, and superiorly it
 
traverses the lower part of the medulla oblongata on its lateral aspect,
 
after which it'enters the restiform body, by which it is conducted to
 
the vermis of the cerebellum. Its fibres are usually regarded as being
 
derived from the thoracic nucleus or column of Clarke.
 
 
 
The ventral spino-cerebellar tract, or tract of Gowers (Fig. 871, 5),
 
is situated chiefly in the lateral column, in front of the dorsal cerebellar tract, close to the outer surface of the cord. It is comma-shaped
 
in section, its dorsal part being broad, but as it extends forwards
 
between the funiculi of the ventral nerve-roots it tapers and enters
 
the ventral column superficially. It begins near the lumbar region
 
of the cord. Superiorly it extends through the medulla oblongata
 
and pons, and afterwards passes along the superior cerebellar peduncle
 
into the cerebellum, terminating in the vermis. It therefore takes an
 
indirect course as compared with that of the dorsal spino-cerebellar
 
tract. Its fibres are crossed and are usually regarded as being derived
 
from the thoracic nucleus and posterior horn of the opposite side. The
 
ventral spino-cerebellar tract contains the spino-thalamic and spinotectal tracts.
 
 
 
The spino-thalamic tract (Fig. 871, 6) consists of fibres which arise
 
as the axons of cells of the dorsal grey matter, around which cells the
 
fibres of the dorsal nerve-roots have terminated. The spino-thalamic
 
fibres cross to the opposite side in the ventral or white commissure,
 
thus giving rise to a spinal inferior sensory decussation or spino-thalamic
 
decussation, as distinguished from the superior sensory decussation in
 
the bulb, called the decussation of the fillets, which is produced by the
 
deep arcuate fibres which arise from the cells of the nucleus gracilis and
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1433
 
 
 
 
 
ucleus cuneatus. The spinothalamic fibres, having crossed in the
 
entral white commissure, ascend in the tract of Gowers, and after
 
raversing the bulb and pons they terminate in the optic thalamus
 
f the side to which they have crossed as a cell-station. It is important
 
d note that there are two sensory decussations —lower or spinal, and
 
pper or bulbar. In unilateral lesions of the spinal cord there would
 
nly be partial anaesthesia on the opposite side; whereas in unilateral
 
:sions of the bulb, involving both the fillet-fibres and the spino-thalamic
 
bres, there would be complete anaesthesia on the opposite side.
 
 
 
The spino-tectal tract (Fig. 871, 6) is also an ascending tract. Its
 
bres are connected with the cells of the ventral cornu of grey matter,
 
hey ascend in conjunction with the ventral spino-cerebellar tract, and
 
ass through the formatio reticularis of the bulb and pons. After
 
lis they decussate with those of the opposite side, forming the fountain
 
ecussation (of Meynert), which lies between the two red nuclei, to
 
duch nuclei the spino-tectal fibres furnish collaterals. After the
 
ecussation the fibres of either side pass to the corresponding superior
 
illiculus of the corpora quadrigemina.
 
 
 
The tracts of the antero-lateral column may be otherwise arranged
 
s follows:
 
 
 
 
 
Ventral Column.
 
 
 
nterior cerebro-spinal tract (descending). (12).
 
 
 
nterior intersegmental (descending)
 
 
 
( 1 4 ) - . ;
 
 
 
ulco-marginal tract (descending)
 
 
 
( 15 )
 
estibulo-spinal tract (descending)
 
 
 
( T 9);
 
 
 
nterior spino-thalamic tract (ascending) ( 7 ).
 
 
 
 
 
Lateral Column.
 
 
 
Lateral cerebro-spinal tract (descending) (11).
 
 
 
Rubro-spinal tract (descending) (16).
 
Tecto-spinal tract (descending) (17).
 
Olivo-spinal tract (descending) (18).
 
Dorsal cerebellar tract (ascending)
 
 
 
( 4 )-.
 
 
 
Anterior spino - cerebellar tract
 
(Gowers, ascending) (5).
 
 
 
Posterior spino-thalamic and spinotectal tracts (ascending) (6).
 
Lateral intersegmental (descending)
 
( 13 )
 
 
 
The spino-thalamic and spino-tectal tracts (ascending) are contained
 
1 the ventral spino-cerebellar tract. A part of the postero-lateral
 
isciculus (Lissauer’s tract) lies superficially in the dorsal part of the
 
iteral column, and it has been described in connection with the dorsal
 
olumn.
 
 
 
 
 
Association Fibres of Antero-lateral Column—Intersegmental Fasciculi.— The
 
 
 
art of the antero-lateral column which is not occupied by the descending and
 
scending tracts is adjacent to the grey matter, and it constitutes the antero,teral ground-bundle. It is divided into two parts—anterior and lateral.
 
 
 
The anterior intersegmental group is situated in the ventral column in front
 
: the ventral cornu of grey matter, and has been already described.
 
 
 
The lateral group occupies the lateral column ventral and medial to the crossed
 
framidal tract.
 
 
 
The portion of the ventro-lateral ground-bundle adjacent to the grey matter,
 
id almost surrounding it, is known as the limiting zone.
 
 
 
The fibres of the entire antero-lateral ground-bundle are association or
 
ngitudinal commissural fibres, which serve to connect the grey matter of sue
 
 
 
 
 
 
 
I 434
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
cessive segments of the spinal cord. They are derived from the cells of the gre
 
matter of the same side, and also of the opposite side, the latter crossing in th
 
ventral or white commissure.
 
 
 
Arteries of the Spinal Canal and Spinal Cord—Arteries of the Spina
 
Canal.—These vessels enter the spinal canal through the intervertebra
 
and sacral foramina. In the cervical region they are branches of th
 
vertebral, deep cervical, and superior intercostal arteries; in th
 
thoracic and lumbar regions they are derived from the dorsal branche
 
of the intercostal lumbar and ilio-lumbar arteries; and in the sacra
 
region they come from the lateral sacral arteries. Within the spina
 
canal each spinal artery divides into three branches—neural or central
 
and anterior and posterior parietal. The neural or central brand
 
pierces the theca of the spinal cord. It supplies the coverings of th
 
cord and the nerve-roots, and it anastomoses with the anterior anc
 
posterior spinal arteries on the cord. This branch is sometimes spokei
 
of as the lateral spinal artery. The parietal branches divide and joii
 
again with one another in such a way that they form five anastomoti(
 
chains in the spinal canal outside the dura mater; of these, one i:
 
antero-median, two antero-lateral, and two postero-lateral.
 
 
 
Arteries of the Spinal Cord.—These are: (i) the anterior spina
 
artery; (2) the posterior spinal arteries, right and left; and (3) th
 
lateral spinal arteries, right and left (neural or central branches jus described in connection with the spinal canal).
 
 
 
The anterior spinal artery is formed by the union of the anterior
 
spinal branches, right and left, of the vertebral arteries. It descend:
 
along the front of the cord in the median line, and is reinforced at
 
regular intervals by the lateral spinal arteries. In this manner ar
 
anterior longitudinal anastomotic chain is formed, which descend:
 
for some distance on the filum terminale.
 
 
 
The anterior spinal branches of the vertebral arteries are seldom of equa
 
size, and often only one is present.
 
 
 
The posterior spinal arteries are two in number, right and left, anc
 
each is a branch of the corresponding vertebral artery. Each vesse
 
descends on the side of the cord in two branches, one being in front
 
of and the other behind the posterior nerve-roots. These are reinforcec
 
by branches from the lateral spinal arteries, and the lateral longitudinal
 
anastomotic chains formed in this manner extend over the entire length
 
of the cord. It will thus be seen that there are five anastomotic
 
chains inside the dura mater in relation to the cord, though they have
 
not quite the same distribution as the extradural; one is antero-median
 
and two on each side postero-lateral. Of these two, one lies in front
 
of and the other behind the posterior nerve-roots.
 
 
 
It is only under very favourable conditions that all these arteries are
 
injected equally.
 
 
 
Veins of the Spinal Column and Spinal Cord—Veins of the Spina)
 
Column.—These veins form two plexuses, extra- and intra-spinal, which
 
for convenience are divided into five groups from behind forward:
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1435
 
 
 
 
 
) posterior extraspinal, (2) posterior intraspinal, (3) veins of the
 
irtebral bodies, (4) anterior intraspinal, (5) anterior extraspinal.
 
 
 
The dorsal spinous venous plexus is situated deeply upon the supernal surface of the neural arches of the vertebrae under cover of the
 
ultifidus spinae muscle. It receives its tributaries from the integuent and muscles of the back, and it communicates with the posterior
 
ngitudinal intraspinal plexus by branches which pierce the ligamenta
 
iva. In the neck the blood is conveyed away from the plexus by
 
uns which open into the vertebral venous plexus around the vertebral
 
tery of each side; in the thoracic region by veins which join the dorsal
 
■anches of the intercostal veins; and in the lumbar region by veins
 
hich join the dorsal branches of the lumbar veins.
 
 
 
The veins of the bodies of the vertebrae (venae basis vertebrae) are
 
mtained within the cancellated tissue of the vertebral bodies. They
 
)mmunicate in front with the anterior extraspinal veins, and posteriorly
 
iey terminate in two venous trunks which, emerging through the
 
 
 
 
 
 
 
 
 
Fig. 872. —Schematic Sections to show Positions of Longitudinal
 
 
 
Arterial and Venous Channels.
 
 
 
vo foramina on the posterior surface of each vertebral body, open
 
ito the transverse communicating branch between the two anterior
 
•ngitudinal intraspinal veins.
 
 
 
The anterior longitudinal intraspinal veins form two anastomotic
 
lains, which are situated on the posterior surfaces of the bodies of
 
le vertebrae, one on either side. They communicate with each other
 
pposite the centre of each body by transverse branches which receive
 
le terminal trunks of the venae basis vertebrae. These transverse
 
ranches pass between the posterior longitudinal ligament and the
 
odies of the vertebrae. Superiorly the anterior intraspinal veins
 
)mmunicate with the vertebral and the transverse or basilar plexuses
 
f veins, and laterally an offset passes outwards through each interertebral foramen, which, with that of the posterior intraspinal vein,
 
)rms a plexus around the adjacent spinal nerve.
 
 
 
The posterior longitudinal intraspinal veins are situated in front of
 
le laminae, one on either side, and they are connected at frequent
 
itervals by transverse branches. They communicate with the dorsal
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
!436
 
 
 
spinous venous plexus by branches which pierce the ligamenta flava.
 
Superiorly they communicate with the marginal sinuses on either side
 
of the foramen magnum and vermiform fossa, which by their union
 
form the occipital sinus. With the marginal sinuses and the anterior
 
intraspinal veins they form a venous ring at the foramen magnum.
 
Laterally each vein sends outwards through the corresponding intervertebral foramen an offset, which, with that of the anterior intraspinal
 
vein, forms a plexus around the adjacent spinal nerve.
 
 
 
The anterior and posterior intraspinal veins are situated between
 
the theca of dura mater and the wall of the spinal canal.
 
 
 
The anterior extraspinal veins form a plexus along the anterior
 
aspect of the bodies of the vertebrae, which is most copious in the neck.
 
On either side it communicates with the vertebral plexus around the
 
vertebral artery in the neck, the intercostal veins in the thoracic region,
 
and the lumbar veins in the lumbar region. It is also connected with
 
the venae basis vertebrae.
 
 
 
Veins of the Spinal Cord.—These vessels lie within the substance
 
of the pia mater, and are disposed as venous chains, one being in front,
 
one behind, and two on either side. The anterior vessel lies over the
 
anterior median fissure beneath the anterior spinal artery; the posterior
 
vessel is also medially placed; and the two lateral vessels are situated
 
one in front of and the other behind the posterior nerve-roots (Fig. 872).
 
Besides these principal chains the veins form a plexus on the surface
 
of the cord. Laterally branches emerge through the intervertebral
 
foramina, which, along with the offsets of the anterior and posterior
 
intraspinal veins, form plexuses around the spinal nerves. From these
 
plexuses the blood is conveyed on either side into the vertebral plexus
 
and deep cervical vein in the neck, and into the intercostal and lumbar
 
veins in the corresponding regions.
 
 
 
Lymphatics.—There are no lymphatic vessels in the spinal cord.
 
Their place is taken by spaces in the outer coat of the arteries, called
 
perivascular spaces, which are in communication with the subarachnoid
 
space.
 
 
 
Development of the Spinal Cord.
 
 
 
The formation of the neural tube from the neural plate and groove is described
 
on pp. 34 and 39. A short general account of the formation of the cord from
 
the tube, and of the spinal nerves, is given on p. 53. Further details are given
 
in the following paragraphs.
 
 
 
The proliferating cells of the early neural tube become confluent and form
 
a syncytium, which is evident in the growing cord to a comparatively late
 
stage. Exhibiting this syncytial character, the ectodermic cells of the wall
 
of the tube undergo proliferation, the wall becomes thickened, and it consists
 
of two kinds of cells—namely, (1) sustentacular or supporting cells, and (2) nervecells proper. The former make the ependyma and neuroglia of the spinal cord,
 
and the latter give rise to the grey and white matter. The loosely arranged
 
syncytial network is known as the myelospongium. This myelospongium becomes
 
condensed internally and externally, and these condensed layers form the internal
 
and external limiting membranes . The wall of the young neural tube is arranged
 
in three layers or zones—namely, (1) inner or ependymal, (2) intermediate or
 
mantle zone, and (3) outer or marginal zone.
 
 
 
The ependymal zone consists of a single layer of elongated cells, connected
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1437
 
 
 
 
 
th the internal limiting membrane. Their bases are directed towards the
 
nen of the neural tube, and from their apices delicate radial fibres pass outrds to the external limiting membrane. Amongst them there are some concuous cells, called germinal cells. These lie close to the wall of the neural
 
?e, and by their proliferation they give rise to ependymal cells and neuroblasts,
 
e latter migrate outwards into the mantle zone.
 
 
 
The mantle layer consists mainly of neuroblasts derived from the lining layer
 
ependymal cells, but smaller neuroglial cells are scattered among- these, and
 
‘ whole is supported by a network of spongioplasm, in which, in fact, the
 
 
 
 
 
 
 
j. 873.—Three Sections from Different Levels of Cord in Embryo
 
 
 
of 4-9 Mm.
 
 
 
ft lower figure, under higher power, shows nerve-fibres leaving ventro-lateral
 
 
 
wall.
 
 
 
dei may be said to be embedded. Neuroglial fibres develop from the neuroil cells, and extend throughout the thickness of the cord, ramifying and joining
 
Tin the spongy basis.
 
 
 
The marginal zone is the peripheral and outlying part of the spongy netrk, forming a definite layer superficial to the mantle zone. It is a region
 
ich will be occupied by the tracts of nerve-fibres as these form, acting as
 
scaffolding or support for them; it increases enormously in thickness as the
 
r asion by fibres progresses.
 
 
 
As just said, the white matter of the cord is made by nerve-fibres growing
 
 
 
 
 
1438
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
in the marginal zone, the grey matter is formed from the mantle zone, and th
 
ependymal layer, when it has ceased to proliferate and give off the cells of th
 
mantle zone, becomes the lining cell layer of the central canal. The cana
 
itself is the remains of the ventral part of the original cavity of the neural tube
 
 
 
Neuroglial cells have many branches, and are spoken of as glia-cells or spidet
 
cells. The neuroglial fibres are fibrillations of the peripheral protoplasm of th
 
cells, from which they become differentiated.
 
 
 
The neuroblasts lie in groups within the mantle layer, and they give ris
 
to the nerve-cells of the spinal cord. Each cell is primarily unipolar and pear
 
shaped. It has a prominent nucleus, and the body is prolonged into a proces
 
or pole, which represents the axon or axis cylinder process of a nerve-fibre. Sub
 
sequently the pear shape is lost, due to the formation of secondary processes o
 
dendrites, the cell being now multipolar.
 
 
 
Formation of the Cord. —The number of neuroblasts within the mantli
 
zone increases rapidly, the multiplication being due to frequent division of th
 
germinal cells in the ependymal zone.
 
 
 
The division of germinal cells is apparently very extensive and rapid
 
There is doubt, however, as to further addition by division of the nucle
 
within the mantle zone; if there is such division, it is probably amitotic
 
as the occurrence of mitotic figures in this zone is very exceptional.
 
 
 
Whatever may be the origin of all the nuclei, they soon show a tendency t(
 
gather more particularly in dorsal and ventral thickenings on each side. Thu:
 
 
 
there occur longitudinal bulgings on eacl
 
side, showing not only on the oute:
 
surface, but also markedly on the in
 
ternal surface, making the prominence:
 
known as the dorsal (or alar) and ventra
 
(or basal) laminae (Fig. 874) which affeci
 
the form of the contained cavity. Ai
 
interlaminar sulcus runs down the sid(
 
wall of the cavity between these tw(
 
laminae.
 
 
 
A semidiagrammatic sectior
 
across the cord of an embryo ai
 
the end of the first month is given
 
in Fig. 874 to illustrate thes*
 
points. The main collections 0:
 
neuroblasts in the mantle zone
 
make the ventral (V) and dorsa'
 
(D) laminae, separated by the
 
sulcus (IL). A floor-plate, (F)
 
connects the two sides and is composed of a thinner ependymal layer with
 
a fairly thick marginal zone; a roof plate (R) is practically only ependymal.
 
The neural crest, described on p. 53, lies beside the tube on each side,
 
and is represented here by a mass of neuroblasts which will become the
 
posterior root ganglion (G); the interganglionic parts of the neural crest
 
(p. 54) have disappeared by this time, leaving the ganglionic masses
 
in position. Differential disposition of neuroblasts in the mantle zone
 
has begun already.
 
 
 
General Formation. —The neuroblasts of the basal lamina make the cells of
 
the anterior grey column, and the fibres of the afferent roots pass out directly
 
from them. Those of the dorsal lamina are utilized in forming the matter of
 
the posterior grey column. The spinal ganglia send nerve-fibres (posterior roots)
 
into the dorsal region of the cord, the ganglia, as seen, being outside the cord
 
from the beginning. The marginal zone carries fibres from the neuroblasts, and
 
thus increases in depth gradually and continuously; in this way the white matter
 
of the cord is laid down round the grey substance. The cavity, becoming
 
relatively smaller, remains only as the central canal', there is some reason to think
 
 
 
 
 
 
 
Fig. 874. —Section across Cord,
 
Semi-diagrammatic, about End
 
of First Month.
 
 
 
(Explanation in text.)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
J 439
 
 
 
 
 
at the dorsal portion of the original cavity is actively obliterated by fusion
 
;tween its walls. The ependymal zone, after its germinal functions have ceased
 
the end of the second month, becomes the ependymal lining of the canal.
 
 
 
The ventral lamina differentiates
 
ore quickly than the dorsal part,
 
id can be described first. In Fig.
 
 
 
74 it can be seen that a tract of
 
ldei ( b ) is present, having a distinct
 
irso-ventral direction and passing
 
edial to the main ventral or ventroteral neuroblastic mass (a). This
 
tract comes early. Its appearance
 
ggests at first a dorso-ventral
 
igration, but such migration is
 
rtainly not present, and the arngement seems only due to the
 
rection of early fibrils in this tract
 
path, directed towards the floorate, where they cross to the other
 
ie.
 
 
 
This early indication of decussation is of interest. For
 
some fundamental but not very
 
evident reason, the passage of
 
impulses—afferent or efferent
 
—to the opposite side seems to
 
be of basic importance, and a
 
glimpse at the drawings given
 
already will make it clear that
 
the floor-plate is the decussating region; the roof-plate does
 
not seem to provide the necessary marginal zone, and is in
 
fact stretched into a transparent cellular layer higher up,
 
so that the commissural fibres
 
have only the floor-plate for
 
their passage. So far, then, as
 
the primary neural tube extends, all commissural fibres
 
pass ventrally, and the tract b
 
might even be spoken of as
 
a ‘ lateral commissure path ’;
 
such a name, however, would
 
not take account of certain
 
other characters, which might
 
be summed up perhaps in a
 
‘ path of least resistance,’ so
 
that, for instance, vessels tend
 
to enlarge and lie in this path.
 
 
 
Without labouring the matter
 
further, it will be enough to direct attention to this ' path,’ to which reference
 
will be made from time to time.
 
 
 
 
 
 
 
Grouping of Ventral Neuroblasts. — Fig. 875 gives tracings from different
 
A els of the cord at 15 mm., showing the modifications found at this period
 
the ventro-lateral group (a of Fig. 874). The groups are not so clearly marked,
 
course, as indicated in the tracings, but are nevertheless quite evident; uC
 
d mC are upper and middle cervical levels, uD and mD are upper and middle
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1440
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
thoracic, and iL and mL are first and middle lumbar levels. The ‘ commissun
 
path ’ already mentioned is shown at b, and the grouping of neuroblasts seems i
 
correspond well with the condition in the adult cord; hence the arrangements i
 
the ventral grey column appear to be attained at an early stage. The group c, i
 
the cervical and upper thoracic sections, increases in size as it is traced upward;
 
It is composed of neuroblasts originating from the ependymal zone at the sam
 
level of origin as. the a group, but separated from this last collection by the pat
 
b ; this suggests that it might be looked on as of the same morphological value a
 
the a group, but of later development. Whether this way of regarding it i
 
justifiable or not, the group is responsible for supplying the hypoglossal nucleu
 
and (possibly) that of the sixth nerve, while the a group, at the hypoglossal leve
 
is apparently taken into the formation of the olive; this will be dealt with in th
 
proper place.
 
 
 
Dorsal Lamina and Associated Formations. —The neuroblasts of the dorsa
 
lamina increase and differentiate slowly, forming a massive but apparent!
 
undifferentiated collection in the second month, when the ventral formation
 
(Fig. 875) are evident. There is at first very little marginal zone over thi
 
dorsal collection, but about the end of the first month the fibrils growing ii
 
from the ganglionic mass, beside the cord, begin to collect as a small bundl
 
(C, Fig. 874) on the dorso-lateral aspect of the neuroblastic mass. This bund!
 
is the earliest sign of the posterior white column, and increases rapidly in size, a
 
the same time extending medially. The bundle is to be identified with thi
 
cuneate fasciculus. The medial extension no doubt helps to form the gracil
 
fasciculus, but this may have some separate formation as well. The postero
 
lateral tract (Lissauer’s zone) begins to form a little later, as the entering fibre;
 
of the posterior root increase in number.
 
 
 
The method of elongation of the posterior horn is not clear; doubtless th<
 
increasing depth of the surrounding white columns has something to do with it
 
but the other factors are not apparent.
 
 
 
The deposition of fibrils within the marginal zone to make the white column!
 
goes on, seemingly, throughout foetal life; they can be recognized in the firs'
 
part of the second month at least, and perhaps earlier than this. It may b(
 
assumed that the shorter fibres are formed first, and occupy the marginal zon<
 
close to the neuroblasts; thus we get the short intersegmental fibres clothing
 
the grey matter. The subsequently developed longer fibres are laid down or
 
these short ones, and the latest developed would be the most superficial; thu;
 
we find long fibres reaching the mid-brain and thalamus, and superficial to these
 
although mixed with them to some extent, fibres running to the cerebellum,
 
a later formation. This, in a general way, agrees with what is known about the
 
position of such tracts in the cord.
 
 
 
The downward-running tracts doubtless follow a comparable regulation ir
 
their disposal, but the matter of decussation is important here. The cerebrospinal fibres, for example, decussate for the most part immediately before entering the cord, and thus pass at once into the b path mentioned above; following
 
this, they reach the space ventral to the posterior horn and Lissauer’s tract, in
 
which they lie as the lateral cerebro-spinal or crossed pyramidal tract. The
 
uncrossed fibres ultimately cross and also enter the b path, from which they reach
 
the anterior horn.
 
 
 
Myelinization. —The tracts are at first made up of axis cylinders alone, and
 
these acquire myelin sheaths subsequently. The time when this occurs differs
 
in the various tracts. The process begins about the fourth or fifth month in
 
the root fibres, and after this appears in the tracts more or less in the order of
 
their formation as laid down above. The pyramidal fibres do not begin to
 
develop their sheaths till about the time of birth, and the process is said to
 
continue until after puberty.
 
 
 
Caudal End of Spinal Cord. —This undergoes certain modifications. It can
 
be seen in Fig. 877 that a tail process, bent dorsally, represents the atrophied
 
remnant, in the early part of the second month, of the large ‘ tail ’ of younger
 
stages. This tail process contains a prolongation from the neural tube; it
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1441
 
 
 
smains up to about the 18 mm. stage, when the atrophied filament vanishes,
 
arrying with it the included neural prolongation. Fig. 876 shows two median
 
mgitudinal sections of the end of the cord in embryos of 16 and 35 mm. repectively, the tail remnant being present in the younger specimen, although
 
rst about to disappear. The neural cell-layers in this remnant are continued
 
ito a canal (c), the walls of which are continuous with the ependymal layers
 
f the cord. A second canal (vc) is seen on its ventral side, the cavity of which
 
pens into the central cavity of the cord (the continuity is not very clear in
 
ledian section). The central cavity of the cord ends in a dilated ventricle,
 
diich seems to be a normal condition at this stage. That part of the neural
 
ibe which corresponds with the quondam tail is evidently disappearing, shows
 
regular growth, and is represented by remnants.
 
 
 
In the 35 mm. embryo the tail has gone, and the caudal neural remnant shows
 
coccygeal vestigial cyst {cyst) where the caudal portion has separated, the
 
 
 
 
 
toirqinal jone
 
/ (ye rtf. comm.)
 
 
 
 
 
 
 
16 mm
 
 
 
 
 
!f- -\coccyK
 
 
 
cyst/ v
 
 
 
 
 
 
 
Fig. 876. —Median Sagittal Sections of Ends of Cords in Sixth and
 
 
 
Ninth Weeks.
 
 
 
Ependymal tissue shown in black. Description in text.
 
 
 
 
 
yrst lying very near the surface. Some nerve-fibres have developed in connection
 
ith this {%/) and pass to the cord itself. Remnants of this canal are seen
 
irther forward, and the ventral canal is seen opening into the ventral part of
 
 
 
le terminal ventricle, as in the younger stage.
 
 
 
After this stage the cord does not grow in length at the same rate as the
 
ertebral column, so that its caudal end gets farther and farther away from the
 
Dccygeal region. Hence, the vestigial cyst remaining in situ with a superficial
 
ttachment, the intervening cell-strands are drawn out in a lengthening conection The main cell masses caudal to the ventricle are drawn up with it,
 
taking the nervous elements found in the upper end of the filum terminate;
 
le rest of the filum is composed of drawn-out pia mater, the included and
 
 
 
fetched nerve-tissue having disappeared.
 
 
 
The coccygeal vestigial cyst enlarges somewhat and develops nerve-tissue
 
)und it, but disappears during the later foetal months; it is a possible cause,
 
y persistence, of certain congenital cysts found near the coccyx.
 
 
 
 
 
9i
 
 
 
 
 
 
 
 
 
1442
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Membranes of Spinal Cord. —The membranes—namely, pia mater, arachnoid
 
and dura mater (theca)—are developed from the mesoderm which invests th
 
neural tube.
 
 
 
Growth of Spinal Cord. —The cord originally occupies the entire length o
 
the spinal canal of the vertebral column. The vertebral column, however
 
grows more rapidly than the cord, so that at the period of birth the cord does no
 
extend lower than the level of the third or fourth lumbar vertebra. Sub
 
sequently its lower limit is the intervertebral disc between the bodies of th
 
first and second lumbar vertebrae. This produces a change in the course o
 
the lumbar, sacral, and coccygeal nerves. In order to reach the level of th
 
intervertebral foramina through which they emerge from the spinal cana
 
they descend almost vertically, and constitute the bundles of nerves known a
 
the cauda equina.
 
 
 
A linear reconstruction of the coccygeal portion of the cord in a 15 mm
 
embryo is given in Fig. 877. It shows the atrophying tail-remnant, with it
 
included piece of neural tissue, but also shows, proximal to this, a portion o
 
nerve-tube truly coccygeal in nature and position, from which take origii
 
four (? or more) nerves behind the coccygeal nerve. These post-coccygea
 
nerves, which have double roots, join with each other and with the coccygea
 
 
 
 
 
 
 
Fig. 877. —Linear Reconstruction of Caudal End (15 Mm.), showing thi
 
Prolongation of Cord into the Tail Filament, and the Presenci
 
of Four Nerves beyond the Coccygeal.
 
 
 
The vertebral levels of the spinal nerves are indicated.
 
 
 
nerve in a series of ill-defined loops. They emerge between the rudimentar]
 
vertebrae caudal to the sacrum. The broken-up post-coccygeal portion of th(
 
cord is in part carried up with the persisting coccygeal portion, and in pari
 
left behind; the intermediate part is drawn out with the filum terminale. Som<
 
nervous matter still persists at the upper end of this structure. The post
 
coccygeal nerves atrophy and disappear, but Rauber has described remains
 
of ganglia and nerves beside the upper part of the filum, which may repre
 
sent remnants of the upper post-coccygeal nerves, drawn up with the cord.
 
 
 
 
 
THE ENCEPHALON.
 
 
 
 
 
The encephalon is the part of the cerebro-spinal axis which if
 
contained within the cranial cavity. It is composed of the medulh
 
oblongata, pons Varolii, cerebellum, and cerebrum. In the embryc
 
it consists of three hollow vesicles.
 
 
 
 
 
Encephalon =
 
 
 
Prosencephalon or Fore-brain.
 
Mesencephalon or Mid-brain.
 
Rhombencephalon or Hind-brain.
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1443
 
 
 
 
 
The subdivisions of the prosencephalon are the telencephalon and
 
he thalamencephalon or diencephalon; the mesencephalon remains
 
mdivided; and the subdivisions of the rhombencephalon are the metncephalon and the myelencephalon.
 
 
 
 
 
Fore-brain or Prosencephalon = { ^alamencephalon or Diencephalon.
 
Mid-brain or Mesencephalon = Mesencephalon.
 
 
 
Hind-brain or Rhombencephalon = { Mydenceplulon.
 
 
 
 
 
rhe various parts of the encephalon which are developed from these
 
ubdivisions will be made evident from the following table:
 
 
 
 
 
Telencephalon
 
 
 
 
 
Thalamencephalon
 
 
 
or
 
 
 
Diencephalon
 
 
 
Mesencephalon
 
 
 
Metencephalon
 
 
 
Myelencephalon
 
 
 
 
 
 
 
 
 
Cerebral Hemispheres.
 
 
 
Lateral Ventricles.
 
 
 
Anterior Part of Third Ventricle.
 
Interventricular Foramina.
 
 
 
Olfactory Lobes.
 
 
 
Posterior Part of Third Ventricle.
 
 
 
Optic Thalami and Corpora Geniculata.
 
Pineal Body.
 
 
 
Interpeduncular Structures.
 
 
 
Pituitary Body.
 
 
 
Optic Nerve and Retina.
 
 
 
Corpora Quadrigemina.
 
 
 
Crura Cerebri.
 
 
 
Aqueduct (of Sylvius).
 
 
 
Cerebellum.
 
 
 
Pons (Varolii).
 
 
 
Pontine Part of the Fourth Ventricle.
 
 
 
 
 
( Medulla Oblongata (or Bulb).
 
 
 
\ Bulbar Part of Fourth Ventricle.
 
 
 
 
 
General Description of the Base and Superior Surface of the
 
 
 
Encephalon.
 
 
 
The inferior aspect of the encephalon is known as the base. In the
 
allowing general description of the parts which it presents the order
 
pursued is, as nearly as possible, from behind forwards and upwards.
 
 
 
The medulla oblongata (or bulb) lies on the under aspect of the
 
:erebellum in the median line, occupying the vallecula which separates
 
the two cerebellar hemispheres. The surface exposed is the ventral
 
surface, which presents (1) the anterior median sulcus, crossed at its
 
tower part by the decussation of the pyramids; (2) the pyramid, on
 
sither side of this sulcus; and (3) the olivary body, external to each
 
pyramid.
 
 
 
The hemispheres of the cerebellum lie one on either side of the
 
medulla oblongata, and they conceal from view the posterior parts
 
of the cerebral hemispheres and the posterior part of the great longitudinal fissure. They are characterized by the laminated arrangement
 
of their nervous matter, the laminae being curved and separated from
 
 
 
 
 
 
 
 
 
1444
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
each other by fissures. Posteriorly the hemispheres are separated fror
 
each other by the posterior notch. When the medulla oblongata i
 
raised, and the cerebellar hemispheres slightly separated from each othei
 
the vallecula is fully exposed, and the inferior vermis is seen lyini
 
deeply in it, with the sulcus vallecula on either side of it.
 
 
 
The pons' (pons Varolii) forms a prominent elevation above th
 
medulla oblongata, the surface exposed being the ventral surface. L
 
the median line this surface presents a longitudinal groove, which i
 
 
 
 
 
Olfactory Bulb
 
Olfactory Tract
 
 
 
 
 
Lateral Sulcus
 
 
 
 
 
Optic Nerve
 
 
 
 
 
Gyrus Rectus
 
 
 
 
 
 
 
Subst. Perfor
 
Ant.
 
 
 
 
 
Tuber Cinere
 
and Infundibi
 
Corpus Mami
 
 
 
 
 
Crus Cerebri
 
 
 
 
 
Area Perforal
 
Post.
 
 
 
 
 
Fifth Nerve
 
Sixth Nerve
 
 
 
Facial Nerve
 
Pars Intermedia
 
 
 
 
 
Auditory Nerve-'
 
Glossopharyngeal Nerve Vagus Nerve
 
 
 
Accessory Nerve
 
 
 
 
 
Oblongata
 
 
 
 
 
Hypoglossal Nerve
 
 
 
 
 
Fig. 878. —The Base of the Encephalon, and the Cranial Nerves.
 
1, frontal lobe (orbital surface); 2, temporal lobe; 3, cerebellum.
 
 
 
 
 
occupied by the basilar artery. On either side the pons becomes th<
 
 
 
middle peduncle of the cerebellum, passing outwards and backwards
 
into the cerebellar hemisphere.
 
 
 
The temporal lobes of the cerebrum are situated in front of the
 
cerebellar hemispheres, and are conspicuous by their prominence.
 
Each terminates anteriorly in a projecting extremity, called the
 
 
 
temporal pole.
 
 
 
The stem of the lateral sulcus lies immediately in front of the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1445
 
 
 
 
 
;mporal lobe, and is occupied by the middle cerebral artery. At the
 
iner end of the stem of the fissure is the depression often referred to
 
5 the vallecula Sylvii or vallecula cerebri.
 
 
 
The frontal lobes of the cerebrum lie in front of the stem of the
 
,teral fissure. The exposed parts are the orbital surfaces, each of
 
hich is separated from its fellow of the opposite side by the great
 
ingitudinal fissure. Each orbital surface presents a straight fissure,
 
died the olfactory sulcus, which is situated near the great longitudinal
 
ssure, and is parallel to it. This sulcus is occupied by the olfactory
 
•act and olfactory bulb.
 
 
 
The crura cerebri, or peduncles, right and left, appear at the upper
 
order of the pons, and soon diverge from each other as they pass
 
awards and upwards to sink into the cerebral hemispheres.
 
 
 
The optic tract of each side winds round the outer and ventral
 
spects of the corresponding crus cerebri. Its course is forwards and
 
lwards towards its fellow of the opposite side.
 
 
 
The optic commissure, or chiasma, connects the two optic tracts
 
fter their convergence.
 
 
 
The optic nerves, right and left, leave the front of the commissure,
 
nd pass forwards and outwards to the optic foramina.
 
 
 
The interpeduncular space is situated in front of and above the
 
ons. It is somewhat diamond-shaped, and its boundaries are as
 
dlows: posteriorly, the divergence of the crura at the upper border
 
f the pons; anteriorly, the optic commissure; and, laterally, the crus
 
erebri and optic tract from behind forwards. The following parts
 
e within this space, in the order named, from behind forwards: (1) the
 
rea perforata posterior; (2) the corpora albicantia or mamillaria;
 
nd (3) the tuber cinereum, with the infundibulum. The structures
 
ccupying the interpeduncular space form for the most part the floor
 
f the third ventricle.
 
 
 
The area perforata posterior or posterior perforated substance
 
 
 
Drresponds to the posterior median angle of the diamond-shaped intereduncular space, and it lies in a deep depression, called the intereduncular fossa (or fossa Tarini). The grey matter which forms it is
 
erforated by openings for the passage of the postero-medial branches
 
f the posterior cerebral arteries.
 
 
 
The corpora mamillaria are situated directly in front of the area
 
erforata posterior, and present the appearance of small, white, peake bodies lying close to the median line.
 
 
 
The tuber cinereum extends from the mammillary bodies to the
 
ptic commissure, and is composed of grey matter. The infundibulum
 
; connected with the tuber cinereum close behind the optic comlissure, and passes downwards to the posterior part of the pituitary
 
ody.
 
 
 
The area perforata anterior or anterior perforated substance of each
 
de coincides with the vallecula at the inner end of the stem of the
 
iteral fissure. It lies outside the interpeduncular space, close to the
 
uter aspect of the optic commissure. It consists of grey matter, which
 
 
 
 
 
I446
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
is perforated by openings for the passage of a few antero-medial branches
 
of the anterior cerebral artery, and numerous antero-lateral branches
 
of the middle cerebral artery. These branches are destined for the
 
nucleus caudatus and nucleus lenticularis of the corpus striatum, the
 
grey matter of which nuclei comes to the surface of the brain at the
 
anterior perforated substance.
 
 
 
The medulla oblongata and pons occupy the basilar groove of the
 
interior of the base of the skull; the cerebellar hemispheres occupy the
 
cerebellar fossae of the occipital bone; the temporal lobes of the cerebrum
 
sink deeply into the lateral divisions of the middle fossa of the base
 
of the skull; the orbital surfaces of the frontal lobes occupy the lateral
 
divisions of the anterior fossa; the stem of the lateral fissure faces the
 
posterior border of the small wing of the sphenoid; the optic commissure lies above the olivary eminence and optic groove of the sphenoid;
 
and the olfactory bulb rests upon one half of the cribriform plate of the
 
ethmoid bone. The olfactory bulb and olfactory tract, essential parts
 
of the brain, occupy the olfactory sulcus on the orbital surface of the
 
frontal lobe near the great longitudinal fissure; and the olfactory filaments pass through the foramina of the cribriform plate of the ethmoid
 
bone on their way from the olfactory cells of the olfactory mucous
 
membrane to the olfactory bulb. Posteriorly the olfactory tract
 
divides into two roots, medial and lateral. The medial root curves
 
inwards behind the ‘ area of Broca ’ to the callosal gyrus. The lateral
 
root passes backwards and laterally across the outer part of the area
 
perforata anterior. The triangular area of grey matter, which is
 
situated between the diverging roots of the olfactory tract, is called
 
the trigonum olfactorium. It is sometimes spoken of as the middle
 
or grey root of the olfactory tract. The area of Broca is situated in
 
front of the medial (inner) root of the olfactory tract, and is continuous
 
with the callosal gyrus.
 
 
 
Superficial Origins of the Cranial Nerves.
 
 
 
The first or olfactory nerve is represented by the filaments which,
 
as has been seen already, have their superficial origin from the lower
 
surfaces of the olfactory bulbs and pass through the cribriform plate.
 
 
 
The second or optic nerve is connected with the lateral extremity
 
of the front part of the optic commissure.
 
 
 
The third or oculo-motor nerve emerges through the oculo-motor
 
sulcus on the inner aspect of the crus cerebri, just above or in front
 
of the pons, and close to the posterior perforated substance.
 
 
 
The fourth or trochlear nerve, having emerged from the upper part
 
of the superior medullary velum, makes its appearance in the interval
 
between the crus cerebri internally and the temporal lobe externally.
 
 
 
The fifth or trigeminal nerve consists of two roots, which emerge close
 
together from the lateral aspect of the ventral surface of the pons.
 
The sensory root is large, and the motor root, which is small, lies above
 
and slightly medial to the sensory root.
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1447
 
 
 
 
 
The sixth or abducent nerve appears at the lower border of the pons
 
ust lateral to the pyramid of the medulla oblongata.
 
 
 
The seventh or facial nerve emerges at the lower border of the pons
 
n front of the restiform body of the medulla oblongata.
 
 
 
The eighth or auditory nerve likewise appears at the lower border of
 
:he pons in front of the restiform body of the medulla oblongata,
 
[t lies on the outer side of the facial nerve.
 
 
 
The N. intermedins is a small nerve which appears between the facial
 
md auditory nerves. It is regarded as the sensory root of the facial
 
lerve.
 
 
 
The ninth or glosso-pharyngeal nerve emerges, in the form of about
 
fix fasciculi, from the postero-lateral sulcus of the medulla oblongata,
 
Detween the olivary body and the restiform body, immediately below
 
the facial nerve.
 
 
 
The tenth or vagus nerve lies directly below the glosso-pharyngeal
 
nerve, and emerges by several fasciculi from the postero-lateral sulcus
 
Df the medulla oblongata in front of the restiform body.
 
 
 
The eleventh or accessory nerve has several roots which lie below
 
the fasciculi of the vagus nerve. These rise (a) from the medulla
 
nblongata and ( b ) the upper part of the lateral column of the spinal
 
:ord as low as the level of the fifth cervical nerve. The first is the
 
zranial origin of the nerve, the second its spinal root. They lie below
 
the fasciculi of the vagus nerve, and external to, or in front of, the
 
posterior roots of the adjacent cervical spinal nerves.
 
 
 
The twelfth or hypoglossal nerve emerges by several fasciculi
 
through the antero-lateral sulcus of the medulla oblongata between
 
the pyramid and the olivary body. These fasciculi lie in line with
 
the sixth nerve superiorly.
 
 
 
Arteries at the Base of the Encephalon. —The arteries which supply
 
the brain are the two vertebral and the two internal carotid arteries.
 
 
 
The vertebral arteries incline medially as they ascend on the ventral
 
aspect of the medulla oblongata, and at the lower border of the pons
 
they unite to form the basilar artery. The branches of each vertebral
 
artery to be noted are as follows: (1) the posterior spinal branch , which
 
arises from the main vessel immediately after it has pierced the dura
 
mater, and descends upon the side of the medulla oblongata to the
 
spinal cord; (2) the anterior spinal branch , which arises higher up than
 
the preceding, and passes downwards and inwards on the ventral aspect
 
of the medulla oblongata to unite with its fellow and form the anterior
 
spinal artery ; and (3) the posterior inferior cerebellar branch, of large
 
size, which arises from the main vessel near the pons, and passes backwards round the medulla oblongata to enter the vallecula of the cerebellum.
 
 
 
The basilar artery extends from the lower border of the pons to the
 
upper border, occupying the basilar groove on its ventral surface.
 
It is formed by the union of the two vertebral arteries, and terminates
 
by dividing into the two posterior cerebral arteries. The branches of
 
the basilar artery to be noted on either side are as follows. (1) the
 
 
 
 
 
 
 
1448 A MANUAL OF ANATOMY
 
 
 
transverse arteries of the pons ; (2) the internal auditory artery , which
 
accompanies the auditory nerve through the meatus auditorius internus; (3) the anterior inferior cerebellar artery , which arises from the
 
basilar about its centre, and passes backwards to the inferior surface of
 
the cerebellar hemisphere; (4) the superior cerebellar artery , which arises
 
from the basilar near its termination, and passes laterally close to the
 
 
 
 
 
 
 
upper border of the pons, and then round the outer side of the crus
 
cerebri to the superior surface of the cerebellar hemisphere; and (5) the
 
posterior cerebral artery , which arises from the termination of the basilar,
 
and passes laterally parallel to the superior cerebellar artery, and then
 
round the crus cerebri to the inferior surface of the occipital lobe. The
 
posterior cerebral and superior cerebellar arteries are separated from
 
 
 
 
 
}
 
 
 
 
 
*
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1449
 
 
 
 
 
iach other by the third and fourth cranial nerves. The branches of
 
;he posterior cerebral artery are: (1) postero-medial, which pass to the
 
posterior perforated substance; (2) postero-lateral, which pass round
 
:he crus cerebri; and (3) posterior choroidal, which pass to the upper
 
Dart of the choroidal fissure.
 
 
 
The internal carotid artery of each side appears at the vallecula
 
:erebri, and there divides into the anterior and middle cerebral arteries.
 
Near its termination it gives off the posterior communicating artery,
 
which passes backwards to join the posterior cerebral artery. It also
 
pves off the anterior choroidal artery, which passes backwards and
 
Dutwards between the crus cerebri and the uncinate gyrus to the lower
 
and anterior part of the choroidal fissure.
 
 
 
The anterior cerebral artery passes forwards and inwards between
 
the optic nerve and the medial root of the olfactory tract, and enters
 
the great longitudinal fissure.
 
 
 
As it is about to enter that
 
fissure it is connected with
 
its fellow of the opposite side
 
by the anterior communicating artery, which is short,
 
but of fairly large size.
 
 
 
Amongst other branches the
 
following are to be noted
 
arising from the anterior
 
cerebral artery: (1) anteromedial, few and inconstant;
 
and (2) antero-lateral, both of
 
which pass to the anterior
 
perforated substance.
 
 
 
The middle cerebral artery,
 
of large size, sinks into the
 
lateral fissure, which it traverses in an outward ‘direction. Before
 
disappearing into the fissure antero-lateral ganglionic branches are to be
 
noted arising from it, which are arranged in two sets, medial and
 
lateral striate, for the corpus striatum and internal capsule.
 
 
 
Circulus Arteriosus.—This is an important communication between
 
the vertebral and internal carotid arterial systems at the base of the
 
brain, which is situated around the interpeduncular space. It is not
 
actually a circle, though so named, but is a heptagon—that is to say,
 
it has seven angles and seven sides.
 
 
 
Beginning at the median line posteriorly, and proceeding forwards
 
on either side to the median line in front, at the great longitudinal
 
fissure, the component arteries of the circle are: (1) the basilar, (2) the
 
posterior cerebral, (3) the posterior communicating, (4) the internal
 
:arotid, (5) the anterior cerebral, and (6) the anterior communicating.
 
These communications serve to insure a uniform supply of arterial
 
fiood to the brain in cases of obstruction to one or other of the principal
 
irterial trunks. The communications also serve to equalize the circu
 
 
 
1. Internal Carotid
 
 
 
2. Middle Cerebral
 
 
 
3. Anterior Cerebral
 
 
 
4. Anterior Communicating
 
 
 
5. Posterior Communicating
 
 
 
6 . Posterior Cerebral
 
 
 
7. Basilar
 
 
 
8 . Superior Cerebellar
 
 
 
9. Transverse Pontine
 
xo. Internal Auditory
 
xr. Anterior Inferior Cerebellar
 
 
 
12. Posterior Inferior Cerebellar
 
 
 
13. Vertebral
 
 
 
14. Anterior Spinal
 
 
 
15. Posterior Spinal
 
 
 
16. Anterior Choroid
 
 
 
17. Posterior Choroid
 
 
 
18. Cential or Ganglionic
 
 
 
19. Central or Ganglionic
 
 
 
20. Central or Ganglionic
 
(Postero-mesial)
 
 
 
‘21. Central or Ganglionic
 
(Postero-lateral)
 
 
 
Fig. 880. —The Arteries at the Base of
 
the Brain, and the Circulus Arteriosus.
 
 
 
 
 
 
 
13 15 14
 
 
 
 
 
 
 
 
 
1450
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
lation of blood through the different parts of the brain, an arrangement
 
which, though doubtless advantageous, cannot be essential, since one
 
or both of the posterior communicating arteries are often very small
 
and sometimes absent.
 
 
 
Superior Surface of the Brain. —The brain is ovoid superiorly, its
 
greatest breadth corresponding to the positions of the parietal eminences
 
of the parietal bones. In the median line it presents a deep cleft,
 
called the longitudinal fissure, which extends from the front to the
 
 
 
 
 
Great Longitudinal
 
Fissjarc
 
 
 
 
 
 
 
Fig. 88i.—The Cerebral Hemispheres (Superior View).
 
Fissure of Rolando—central fissure.
 
 
 
 
 
back, and divides it into two hemispheres, right and left. This fissure
 
is occupied by a process of the dura mater, called the falx cerebri, and
 
the corpus callosum lies at its deep part. In front of the corpus
 
callosum the fissure extends down to, and is visible on, the base of the
 
brain, but behind the corpus callosum it only extends to the level of the
 
tentorium cerebelli, which separates the cerebellum from the posterior
 
parts of the cerebral hemispheres. The fissure, therefore, in this situation is not visible inferiorly until the cerebellum and the tentorium
 
cerebelli have been removed.
 
 
 
 
 
/
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1451
 
 
 
 
 
Each hemisphere is semi-ovoid, its medial surface being flat. The
 
anterior and posterior extremities are rounded, the former being the
 
thicker of the two. The anterior extremity is known as the frontal
 
pole, and the posterior extremity forms the occipital pole. The surface
 
of each hemisphere consists of grey matter, which is spoken of as the
 
cerebral cortex. Superiorly and externally it is convex in adaptation
 
to the concavity of the vault of the cranium. It is broken up into a
 
number of tortuous eminences, called gyri or convolutions, and these
 
are separated from each other by clefts, called sulci or fissures. The
 
surfaces of the gyri which bound the sulci are covered with grey
 
matter, like their exterior. The pia mater closely covers the gyri, and
 
also dips into the sulci, so as to cover the opposed surfaces of the gyri.
 
The arachnoid membrane, however, does not dip into the sulci, but
 
passes over them. The sulci are of various depths, but the average
 
depth is about J inch.
 
 
 
RHOMBENCEPHALON.
 
 
 
1. The Medulla Oblongata.
 
 
 
The medulla oblongata (or bulb) is continuous with the spinal cord,
 
and extends from the lower margin of the foramen magnum of the
 
occipital bone to the lower border of the pons. Its direction is upwards
 
and forwards, and it measures 1 inch in length, f inch in breadth at
 
the widest part, and fully \ inch in thickness. Interiorly its girth
 
corresponds with that of the spinal cord, but it widens superiorly, so
 
that it is somewhat pyramidal. Its ventral surface faces the basilar
 
groove of the occipital bone, and its dorsal surface is directed towards
 
the vallecula of the cerebellum.
 
 
 
The bulb is composed of two symmetrical halves, its bilateral
 
symmetry being indicated superficially by upward prolongations of
 
the ventral or anterior sulcus and dorsal or posterior median septum
 
of the spinal cord. The anterior median fissure extends as high as the
 
lower border of the pons, where it expands slightly and forms a blind
 
recess, called the foramen ccecum. In its lower part this fissure is interrupted and crossed by bundles of nerve-fibres, which are derived
 
from the inner three-fourths of each pyramid, the decussation thus
 
formed being known as the decussation of the pyramids, or motor
 
decussation. The posterior median septum only extends along the lower
 
half of the bulb, and it terminates superiorly at the point of divergence
 
of the margins of the fourth ventricle.
 
 
 
Each half of the bulb presents two grooves. The antero-lateral
 
sulcus is situated between the pyramid and the olivary body, and along
 
this sulcus the roots of the hypoglossal nerve emerge in line with the
 
ventral roots of the spinal nerves. Whilst, however, the latter are
 
spread over a certain area, the hypoglossal roots emerge along a straight
 
line corresponding to the ventro-lateral sulcus of the bulb. This sulcus
 
is not represented on the surface of the spinal cord. The posterolateral sulcus lies on the dorso-lateral aspect of the olivary body. Along
 
 
 
 
 
1452
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
this sulcus, in order from above downwards, there are (i) the roots of
 
the glosso-pharyngeal nerve, (2) the funiculi of the vagus nerve, and
 
(3) the funiculi of the bulbar part of the accessory nerve.
 
 
 
The bulb in its lower half contains a prolongation of the central
 
canal of the spinal cord. This part of the bulb is spoken of as the
 
closed part , and it extends as high as the level of the lower point
 
of the ventricle. In the upper half of the bulb the central canal
 
opens out at this level into the ^fourth ventricle, and the dorsal
 
aspect of the bulb forms the lower,.or bulbar half of the floor of the
 
fourth ventricle. The upper half of. the bulb is therefore spoken of as
 
the open part.
 
 
 
 
 
 
 
Optic Commissure
 
 
 
; Optic Nerve
 
Infundibulum, - ~
 
 
 
Tuber Cinereum '■» * # „ . „
 
 
 
C Optic Tract
 
 
 
Mamillary Body . /
 
 
 
Third Nerve
 
 
 
Mesial Root of Optic Tract '
 
 
 
Lateral Root of Optic Tract
 
Lateral Geniculate Body
 
 
 
 
 
Post.Perforated Subst.
 
 
 
 
 
Fourth Nerve
 
 
 
 
 
Sixth Nerve
 
 
 
 
 
Root of Fifth Nerve
 
Root of Fifth Nerve
 
 
 
 
 
Facial Nerve
 
 
 
Pars Intermedia
 
Auditory Nerve -
 
Glosso-pharyngeal Nerve -Vagus Nerve
 
Superficial Arcuate Fibres—
 
 
 
Accessory Nerve-"
 
 
 
First and Second Cervical Nerves;^
 
 
 
 
 
Middle Peduncle of
 
Cerebellum
 
 
 
Inferior Peduncle
 
- — Hypoglossal Nerve
 
..Anterior Median Fissure
 
 
 
Decussation of the Pyramids
 
 
 
 
 
Fig. 882. —The Medulla Oblongata, Pons, and Interpeduncular Region.
 
C.C., crus cerebri; P., pyramid; O.B., olivary body.
 
 
 
 
 
The surface of each half of the bulb is divided into three areas by
 
the above-mentioned sulci, with the corresponding nerve funiculi.
 
These surface areas are ventral, lateral, and dorsal.
 
 
 
Ventral or Anterior Area.—This superficial area is situated between
 
the median and the antero-lateral sulcus, along which the funiculi
 
of the hypoglossal nerve emerge. It constitutes the pyramid of the
 
bulb. The two pyramids, right and left, represent the motor tracts
 
of the bulb. As regards position, the pyramid is like the anterior
 
column of the spinal cord, and it consists of bundles of nerve-fibres
 
disposed longitudinally. Inferiorly it is somewhat narrow, but it
 
widens superiorly. At the lower border of the pons it undergoes a
 
slight constriction, after which it sinks into the pons. As it traverses
 
the pons its funiculi become separated into several strata, and these
 
are gathered together at the upper border of the pons into the crus
 
cerebri of the corresponding side.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1453
 
 
 
 
 
Inferiorly each pyramid is disposed in two parts—medial and lateral.
 
The medial portion represents as a rule the inner three-fourths, and
 
its fibres cross to the opposite side in the lower part of the ventral
 
median sulcus of the bulb. Thereafter they sink deeply into the dorsal
 
part of the lateral column of the spinal cord on the side to which they
 
have crossed, where they constitute the crossed pyramidal or lateral
 
cerebro-spinal tract. The intercrossing of fibres which takes place in
 
the lower part of the ventral median fissure of the bulb is called the
 
decussation of the pyramids, or the motor decussation, and, as stated, it
 
usually involves the fibres of the inner three-fourths of the pyramid.
 
 
 
The lateral portion of the pyramid represents as a rule the lateral
 
fourth, and its fibres take no part in the decussation. The path of
 
most of them is downwards into the anterior column of the spinal cord
 
of the same side, where they lie close to the anterior median fissure of the
 
cord and constitute the direct pyramidal or anterior cerebro-spinal
 
tract. A few of them, however, descend into the lateral column of
 
the same side, and constitute the uncrossed lateral pyramidal tract.
 
 
 
The pyramid of the bulb, therefore, only corresponds topographically
 
with the anterior column of the spinal cord. The direct cerebro-spinal
 
tract of the anterior column of the cord forms the greater part of the
 
lateral fourth of the corresponding pyramid of the bulb; and the crossed
 
cerebro-spinal tract of the lateral column of the cord forms the medial
 
three-fourths of the pyramid of the opposite side. The remainder of
 
the anterior column of the cord sinks deeply into the bulb and lies on
 
the dorsal aspect of the pyramid.
 
 
 
The ventral surface of each pyramid is crossed above the level of
 
the decussation of the pyramids by the anterior superficial arcuate
 
fibres , which emerge from the ventral median fissure and take an
 
arched course outwards and then backwards to the inferior cerebellar
 
peduncle.
 
 
 
The sixth cranial nerve emerges close to the lower border of the
 
pons, immediately lateral to the pyramid, and in line with the funiculi
 
of the hypoglossal nerve as these leave the ventro-lateral sulcus.
 
 
 
Lateral Area of the Medulla Oblongata.— This superficial area is
 
situated behind the funiculi of the hypoglossal nerve. Superiorly the
 
oval eminence, called the olive, is included in it. Inferiorly it has the
 
appearance of being a prolongation of the lateral column of the spinal
 
cord, but this is not the case. The crossed cerebro-spinal tract of the
 
lateral column of the cord sweeps obliquely across to the opposite side,
 
where it forms the greater part of the pyramid of that side. The
 
parts, therefore, of the lateral column of the cord which form the
 
lateral area of the bulb below the olive are (1) the dorsal or direct spinocerebellar tract, (2) the ventral spino-cerebellar tract, and (3) the lateral
 
intersegmental bundle. The dorsal spino-cerebellar tract, as it ascends,
 
soon inclines obliquely backwards to join the inferior peduncle. The
 
ventral spino-cerebellar tract and intersegmental bundle ascend until
 
they reach the lower end of the olive. They then in part sink deeply,
 
and ascend to the pons on the dorsal or deep aspect of the olive. Most
 
 
 
 
 
T 454
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
of the cerebellar fibres, however, remain on the surface, and ascend in
 
the small interval which lies between the outer part of the olive and
 
the funiculi of the glosso-pharyngeal and vagus nerves.
 
 
 
 
 
 
 
Fig. 883.—A Sketch to show
 
the Disposition of Spinocerebellar Fibres in Lateral Region of Medulla.
 
 
 
 
 
The lateral area of the bulb below the
 
olive thus represents the dorsal or direct
 
spino-cerebellar tract, ventral spino-cerebellar tract, and, deeply, the lateral
 
ground-bundle of the lateral column of
 
the spinal cord of the same side (Fig. 883).
 
 
 
Superiorly, as stated, the lateral area
 
presents an oval eminence, called the
 
olive. It lies between the funiculi of the
 
hypoglossal nerve on the one hand, and
 
the funiculi of the glosso-pharyngeal and
 
vagus nerves on the other, with the
 
intervention of some ascending fibres
 
belonging to the ventral spino-cerebellar
 
tract. Its long axis is placed vertically,
 
and in this direction it measures about
 
J inch. Superiorly it is separated from
 
the pons by a deep transverse groove, and
 
interiorly the anterior superficial arcuate
 
fibres arch over its lower part.
 
 
 
At the lower border of the pons,
 
lateral to the upper end of the olive, the
 
facial and auditory nerves make their
 
appearance. The facial nerve is in line
 
 
 
 
 
The dorsal fibres (interrupted
 
lines) run to inferior peduncle, therefore have a
 
dorsal tendency as they
 
ascend, covering in the
 
spinal root of fifth nerve,
 
which is making a slight
 
prominence, the tuberculum
 
gelatinosum (T). The ventral fibres (Gowers’ tract)
 
are dotted. The arrows
 
indicate many fibres from
 
other parts (olives, etc.),
 
helping to complete the
 
peduncle. C, G, cuneate
 
and gracile tubercles ;
 
P.R.O., position of pallidorubro-olivarv tract.
 
 
 
 
 
closed and open part of the
 
lower and upper.
 
 
 
 
 
with the roots of the glosso-pharyngeal
 
nerve. The auditory nerve appears lateral
 
to the facial nerve, and between the two
 
is the small pars intermedia (of Wrisberg ).
 
 
 
Dorsal or Posterior Area of the Medulla
 
Oblongata.—This superficial area is limited
 
in front by the sulcus containing the
 
funiculi of the glosso-pharyngeal, vagus,
 
and bulbar part of the spinal accessory
 
nerves. Posteriorly its lower half extends
 
as far as the dorsal median fissure, and
 
its upper half extends only as far as the
 
lateral boundary of the lower or bulbar
 
half of the floor of the fourth ventricle.
 
Inasmuch as this area belongs to both the
 
bulb, it will be considered in two sections—
 
 
 
 
 
Lower Portion of Posterior Area. —This, it has been shown, is limited
 
behind by the dorsal median fissure, and it is in direct continuity with
 
the dorsal column of the spinal cord of the same side, which is composed
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
*455
 
 
 
 
 
>f the gracile and cuneate columns. It presents three longitudinal
 
minences—namely, the funiculus gracilis, funiculus cuneatus, and
 
uniculus gelatinosus.
 
 
 
The funiculus gracilis is a prolongation of the column of the spinal
 
ord, and lies close to the dorsal median fissure. The funiculus cuneatus
 
3 a prolongation of the column of the cord, and lies lateral to the
 
uniculus gracilis, from which it is separated by an upward continuation
 
>f the dorsal intermediate or paramedian furrow of the cord.
 
 
 
At the lower level of the ventricle each of these two funiculi
 
)ecomes enlarged and terminates in a prominence or bulb. The enargement formed by the funiculus
 
;racilis is called the clava, or gracile
 
ubercle, and that formed by the funi:ulus cuneatus is termed the cuneate
 
ubercle. The two clavae, right and left,
 
ie on either side of the lower angle of
 
he fourth ventricle, and as the bulb
 
>pens out dorsally at this level to form
 
he lower or bulbar half of the floor of
 
he fourth ventricle each clava is dis)laced laterally. An angular interval
 
low separates the two clavae, and the
 
irolongation of the central canal of the
 
pinal cord through the lower or closed
 
>art of the bulb opens into the fourth
 
ventricle in the angle between the two
 
:lavae.
 
 
 
The funiculus gracilis, with its tu>ercle, and the funiculus cuneatus, with
 
ts cuneate tubercle, are to a large exent produced by the collections of grey
 
natter which they contain—namely, the
 
mcleus gracilis and nucleus cuneatus.
 
 
 
The funiculus gelatinosus is situated
 
>n the outer side of the funiculus cuneatus, between it and the funi:uli of the bulbar part of the spinal accessory nerve. It is produced
 
>y the substantia gelatinosa (of the spinal cord), which is close to the
 
urface in the lower or closed part of the bulb. Interiorly the funiculus
 
s narrow, but it widens as it ascends, and superiorly it terminates
 
n an enlarged extremity, called the spinal tract of the trigeminal or
 
uberculum gelatinosum.
 
 
 
The funiculus and tubercle are covered by a thin layer of longiudinal nerve-fibres which represent the spinal or descending sensory
 
oot of the fifth cranial nerve.
 
 
 
Upper Portion of Posterior Area.— This belongs to the upper or open
 
>art of the bulb, and extends as far as the lateral boundary of the
 
ower or bulbar half of the floor of the fourth ventricle. It presents
 
l prominent round tract, called the restiforrn body , which is situated
 
 
 
 
 
 
 
Fig. 884.—Posterior View
 
of Medulla.
 
 
 
G, C, gracile and cuneate tubercles ; g, c, corresponding
 
tracts; F, gelatinous tubercle; O, obex.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1456
 
 
 
between the lower half of the floor of the fourth ventricle and the
 
funiculi of the vagus and glosso-pharyngeal nerves. Its direction
 
is upwards, outwards, and backwards, and it enters the corresponding hemisphere of the cerebellum. It is otherwise known as the
 
 
 
inferior cerebellar peduncle.
 
 
 
The inferior peduncle succeeds to the funiculus gracilis and funiculus
 
cuneatus of the lower portion of the posterior area of the bulb, but
 
it is quite distinct from these funiculi, and receives no fibres from
 
them. The sources of its fibres will be given in connection with
 
the internal structure of the bulb (see p. 1463). Meanwhile, it is
 
 
 
 
 
 
 
Fig. 885.—Section through Medulla just above Decussation of Pyramids: Shows the Prominence of Spinal Tract of Fifth Nerve.
 
 
 
F is the dorsal spino-cerebellar tract immediately ventral to this, and G is the
 
 
 
ventral tract.
 
 
 
clear that it constitutes the great tract of connection between the
 
cerebellar hemisphere, the bulb, and the spinal cord.
 
 
 
The restiform body becomes conspicuous above the level of the
 
cuneate tubercle, and forms the lateral boundary of the lower or
 
bulbar half of the floor of the fourth ventricle.
 
 
 
Internal Structure of the Medulla Oblongata. —Each half of the
 
bulb is composed of grey nervous matter and tracts of white nervous
 
matter.
 
 
 
Grey Matter. —The grey matter lies largely in the interior. Over
 
the dorsal aspect of the upper or open part of the bulb, however,
 
it comes to the surface, and covers the lower or bulbar half of the
 
floor of the fourth ventricle.
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1457
 
 
 
 
 
As compared with the grey matter of the spinal cord, it presents
 
mportant modifications, and its component parts are as follows:
 
 
 
1. Substantia or formatio reticularis.
 
 
 
2. A thick layer of grey matter around the central canal in the
 
 
 
lower or closed part of the bulb.
 
 
 
 
 
 
 
Fig. 886.—The Decussation of the Pyramids: Scheme representing the
 
Passage of the Various Tracts from the Spinal Cord to the Medulla
 
(L. Testut’s ‘ Anatomie Humaine ’).
 
 
 
 
 
a. Pons
 
 
 
b. Medulla Oblongata (anterior aspect)
 
 
 
c. Decussation of the Pyramids
 
 
 
d. Section of the Cervical Spinal Cord
 
 
 
1. Anterior Cerebro-spinal Tract
 
 
 
2. Lateral Cerebro-spinal Tract
 
 
 
3. Sensory Tract
 
 
 
 
 
3'. Nucleus Gracilis et Nucleus Cuneatus
 
 
 
4. Antero-lateral Intersegmental Tract
 
 
 
5. Anterior Pyramid
 
 
 
6. Fillet or Lemniscus
 
 
 
7. Posterior Longitudinal Bundle
 
 
 
8. Ventral Cerebellar Tract
 
 
 
9. Dorsal Cerebellar Tract
 
 
 
 
 
3. A thick layer of grey matter over the floor of the fourth
 
 
 
ventricle in the upper or open part of the bulb.
 
 
 
4. Substantia gelatinosa (nucleus of spinal tract, N. V.).
 
 
 
5. Nuclei of grey matter.
 
 
 
The modifications undergone by the grey matter of the bulb in
 
ts lower or closed part are brought about by the decussation of the
 
 
 
92
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1458
 
 
 
pyramids. The nerve funiculi of the lateral cerebro-spinal tract
 
of the spinal cord, on one side as they are traced upwards, pass through
 
the base of the ventral grey column of that side, and then cross in the
 
lower part of the ventral median fissure of the bulb to the pyramid
 
of the opposite side, of which they form the inner and larger part.
 
The nerve funiculi of the tract of the other side are disposed in a
 
similar manner. The ventral grey column of either side is thus broken
 
up by the corresponding crossed pyramidal tract. Its basal part
 
remains on the ventral and lateral aspects of the central canal, but
 
its caput is detached and displaced laterally by the pyramid and olive
 
of the same side (see Fig. 887).
 
 
 
The dorsal horn of grey matter is gradually displaced laterally and
 
ventralwards, in the lower or closed part of the bulb, by the funiculus
 
gracilis and funiculus cuneatus. Its basal part remains on the dorsal
 
and lateral aspects of the central canal; its cervix is broken up into
 
a network by intersecting nerve-fibres; and its caput is thereby detached.
 
 
 
 
 
 
 
Fig. 887.— Schematic Sections showing Decussation of Pyramids with
 
the Destruction of Base of Ventral Grey Column (Testut).
 
 
 
The caput lies close to the detached caput of the ventral grey matter,
 
but does not blend with it.
 
 
 
Substantia or Formatio Reticularis. —The grey matter of the detached caput of the ventral grey cornu is broken up into a network
 
by intersecting nerve-fibres, which run longitudinally and transversely. This reticulum, augmented by the network formed in
 
the cervix of the dorsal grey cornu, constitutes the substantia or
 
formatio reticularis of the bulb. It lies deeply within the bulb, dorsal
 
to the olive and pyramid of the same side, and it consists of grey
 
matter, longitudinal and transverse nerve-fibres, and some nerve-cells.
 
 
 
The funiculi of the hypoglossal nerve, as they pass forwards to
 
the ventro-lateral sulcus of the bulb, divide the formatio reticularis
 
into two parts—lateral and medial (Fig. 891). The lateral portion is
 
situated behind the olive, and is called the formatio reticularis grisea,
 
from the large amount of grey matter, with nerve-cells, which it
 
contains. The medial portion is situated behind the pyramid, and is
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1459
 
 
 
 
 
illed the formatio reticularis alba. It contains little grey matter
 
nd few nerve-cells.
 
 
 
Central Grey Matter. —The grey matter which surrounds the
 
jntral canal in the lower or closed part of the bulb is derived from
 
le basal portions of the ventral and dorsal grey columns of the upper
 
art of the spinal cord. In the upper or open part of the bulb this
 
mtral grey matter spreads out and forms a thick layer over the
 
wer or bulbar part of the floor of the fourth ventricle. The medial
 
%rt of this layer represents the basal part of the ventral grey horn,
 
id it contains the hypoglossal nucleus. The lateral part represents
 
le basal part of the dorsal grey horn, and it contains vagus, glossoharyngeal, and vestibular nuclei.
 
 
 
The hypoglossal nucleus is frequently spoken of as ' morphologically continuous with ’ or ‘ representing ’ the ventral grey
 
column above the cervical nerves. This continuity, however,
 
is not an actual anatomical fact; it exists only in the site of
 
ependymal zone origin of the neuroblasts concerned in forming
 
the nuclei. The ordinary motor cells of the ventral grey column
 
in the cord have been derived from the lower part of the ependymal zone, from which they have migrated to form the ventral
 
portion of the marginal zone. Later, when the collections of
 
neuroblasts in the ventral horn have already settled into something approaching their final arrangements, a secondary output
 
of neuroblasts frees itself from the ependymal zone in the same
 
region, but does not migrate any further; this, then, might be
 
looked on as of the same ependymal or original value as the
 
ventral cells, although not anatomically continuous with them.
 
It is from this secondary formation, which is found in the
 
cervical and hind-brain regions, that the hypoglossal nucleus
 
is formed; possibly the sixth nucleus owns a like origin, but
 
this cannot be said with certainty. The other nuclei mentioned
 
in the preceding paragraph are not concerned in this development in any way.
 
 
 
Substantia Gelatinosa (Fig. 885).—This caps the detached and
 
splaced caput of the dorsal horn of grey matter. Having increased
 
 
 
amount owing to the presence of root-fibres of the fifth nerves
 
id lying close to the surface, it gives rise to the tuberculum gelatinosum,
 
metimes referred to simplv as the ‘ spinal tract of the fifth nerve.
 
 
 
Nuclei of Grey Matter.— The nuclei, which will be considered in
 
is place, are as follows:
 
 
 
1. Nucleus gracilis.
 
 
 
2. Nucleus cuneatus.
 
 
 
3. Olivary nuclei.
 
 
 
4. Arcuate nucleus.
 
 
 
5. Nucleus lateralis.
 
 
 
The nucleus gracilis is a collection of grey matter within the funiclis gracilis. For the most part it is connected with the grey matter
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1460
 
 
 
on the dorsal and lateral aspects of the central canal, and it ma]
 
be regarded as being in large part an extension from the basal par
 
of the dorsal grey cornu. It is elongated, and increases in size a:
 
it ascends. It gives rise to the prominence of the funiculus gracilis
 
and to the clava, and the fibres of the funiculus gracilis, as they ascend
 
terminate at intervals around the cells of the nucleus (see Fig. 885).
 
 
 
The nucleus cuneatus is a collection of grey matter within th<
 
funiculus cuneatus. It is a direct extension from the basal part 0
 
 
 
 
 
 
 
Fig. 888.—The Formatio Reticularis of the Medulla Oblongata, showi
 
by a Horizontal Section passing through the Middle of the Olivary
 
Body (Demi-schematic) (L. Testut’s ‘ Anatomie Humaine ').
 
 
 
 
 
1. Anterior Median Fissure
 
 
 
2. Fourth Ventricle
 
 
 
3. Formatio Reticularis
 
3'. Reticularis Alba
 
 
 
3". Reticularis Grisea
 
 
 
4. Raphe
 
 
 
5. Anterior Pyramid
 
 
 
6. Lemniscus
 
 
 
7. Inferior Olive with the two
 
 
 
Accessory Nuclei
 
 
 
 
 
7'. Peduncle of Olivary Body
 
 
 
8. Hypoglossal Nerve
 
8'. Hypoglossal Nucleus
 
 
 
9. Vagus Nerve
 
 
 
g'. Terminal Nucleus of Vagus
 
Nerve
 
 
 
10. External Dorsal Vestibular
 
Nucleus
 
 
 
xx. Nucleus Ambiguus
 
 
 
12. Nucleus Gracilis
 
 
 
 
 
13. Nucleus Cuneatus
 
 
 
14. Caput of Posterior Cornu
 
14'. Lower Sensory Root of Fift
 
 
 
Nerve
 
 
 
15. Fasciculus Solitarius
 
 
 
16. External Anterior Arcuat
 
 
 
Fibres
 
 
 
16'. Arcuate Nucleus
 
 
 
17. Lateral Nucleus
 
 
 
 
 
the dorsal grey cornu, which lies on the dorsal and lateral aspect:
 
of the central canal. Like the nucleus gracilis it is elongated, anc
 
increases in size as it ascends. It gives rise to the prominence 0:
 
the funiculus cuneatus and to the cuneate tubercle, and the fibre:
 
of the funiculus cuneatus, as they ascend, terminate at interval:
 
around the cells of the nucleus.
 
 
 
 
 
Lateral to the nucleus cuneatus there is a small collection of grey matter
 
which is known as the external or accessory cuneate nucleus. It is on a highe:
 
level than the decussation of the pyramids, and it may be regarded as a detachec
 
portion of the substantia gelatinosa.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1461
 
 
 
 
 
The olivary nuclei are associated with the olive, and are three in
 
imber—inferior, and two accessory (medial and dorsal).
 
 
 
The superior olivary nucleus is situated in the dorsal or tegmental part of
 
5 pons, and is not developmentally associated with those now dealt with.
 
 
 
 
 
The inferior olivary nucleus, which is the chief nucleus, is situated
 
thin the olive. As seen in transverse sections through the olive,
 
appears (Fig. 889) as a wavy lamina of grey matter, curved in such a
 
inner as to form an incomplete capsule, which encloses white matter.
 
 
 
 
 
 
 
Nucl. Grac.
 
 
 
 
 
Nucl. Cun.
 
 
 
— Fasc. Solitar.
 
 
 
Sp. Nucleus of
 
Trigeminal
 
Sp. Root Fibres of
 
Trigeminal
 
Med. Longit. Fasc.
 
(Post. Longit. Bundle)
 
Nucl. Ambiguus
 
Lateral Nucleus
 
 
 
Ant. Sp. Cerebellar
 
Fasc. (Gowers)
 
 
 
Dorsal Acc. 01 .
 
 
 
 
 
ig. 889.—Section through the Lower Half of Inferior Olive (shows
 
also the Medial and Dorsal Accessory Olives).
 
 
 
 
 
racile and cuneate nuclei are seen in position, but spinal tract of fifth is separated
 
from surface by fibres passing to inferior peduncle; these are dorsal spinocerebellar and fibres from olive from opposite side; some fibres from olive
 
pass between the nucleus and the nerve tract. Arrows show the direction
 
of fibres on one side. The upper ones come from the dorsal nuclei and fi th
 
nucleus, and run ventrallv to decussate. The lower fibies are running
 
dorsally, and come mainly from opposite olive, and some from same side.
 
 
 
 
 
he open part of the capsule is called the hilum, and is diiected
 
)wards the median line, but it stops short of either end of the nucleus.
 
 
 
great many nerve-fibres pass through the hilum, some inwards
 
nd others outwards, and these form what is known as the olivary
 
eduncle. The wavy lamina is traversed by nerve-fibres..
 
 
 
The medial accessory and dorsal accessory olivary nuclei are situated
 
n the medial and dorsal aspects respectively of the inferior or chiet
 
fivary nucleus, from which, however, they are distinct. Each consts of a band of grey matter, and the upper part of the medial
 
xessory nucleus lies opposite the hilum of the chief nucleus.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1462
 
 
 
Structure of Inferior Olivary Nucleus. —The wavy lamina consists
 
of many small nerve-cells and nerve-fibres which traverse it. The
 
axons of the nerve-cells leave the nucleus as nerve-fibres, and pass
 
to the raphe of the bulb. Some of the nerve-fibres which traverse
 
the wavy grey lamina terminate in connection with its cells, and
 
other fibres pass through it (see Fig. 889).
 
 
 
There are at least two fibre tracts (in addition to those passing
 
into the inferior peduncle) which connect the inferior olive with
 
more distant parts of the nervous system, and are recognizable
 
in sections; little is actually known about them otherwise. The
 
smaller one (olivo-spinal or Helweg’s tract) lies on the surface
 
of the lower medulla and cord immediately in front of the
 
ventral spino-cerebellar fibres. The upper tract, much larger
 
and longer, is the tractus pallido-rubro-olivaris, a name describing
 
its apparent connections.
 
 
 
The structure of the two accessory olivary nuclei corresponds to
 
that of the chief or inferior olivary nucleus.
 
 
 
Arcuate Nucleus. —This nucleus (seen in Fig. 889) consists of a
 
lamina of grey matter which lies upon the ventral aspect of the pyramid
 
of the bulb above the level of the decussation of the pyramids, and
 
beneath the anterior superficial arcuate fibres as they arch outwards
 
over the pyramid after emerging from the ventral median fissure.
 
Superiorly it lies over the medial aspect of the pyramid close to the
 
ventral median fissure. It contains small nerve-cells, in connection
 
with which some of the anterior superficial arcuate fibres terminate,
 
whilst others arise as axons of the cells, and many of them pass over
 
the nucleus without entering it.
 
 
 
Fibres of various sorts, which may be termed in general
 
circumolivary, may be found turning over the lower part of the
 
olive. Some are superficial arcuate fibres, as just described,
 
but others may come apparently from the pyramid, and others
 
again, associated with the ponto-bulbar body, may be really of
 
the nature of aberrant pontine fibres.
 
 
 
Nucleus Lateralis. —This is a special collection of nerve-cells in
 
that portion of the formatio reticularis grisea which lies on the dorsolateral aspect of the olive. It is situated deeply between the olive
 
and the substantia gelatinosa (see Fig. 889).
 
 
 
White Matter of the Medulla Oblongata. —The white matter is
 
situated chiefly on the surface. Over the dorsal aspect of the upper
 
or open part of the bulb, however, the grey matter comes to the
 
surface, and covers the lower or bulbar half of the floor of the fourth
 
ventricle. The white matter is disposed in tracts or strands which
 
are chiefly longitudinal, but a few run transversely in an arched
 
manner. The tracts are as follows:
 
 
 
1. Pyramidal tract (cerebro-spinal tract).
 
 
 
2. Dorsal spino-cerebellar tract (direct cerebellar tract).
 
 
 
3. Ventral spino-cerebellar tract (tract of Gowers).
 
 
 
 
 
/
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1463
 
 
 
4. Restiform body (inferior cerebellar peduncle).
 
 
 
5. Funiculus cuneatus.
 
 
 
6. Funiculus gracilis.
 
 
 
7. Medial or posterior longitudinal bundle.
 
 
 
8. Tecto-spinal tract.
 
 
 
g. Rubro-spinal tract.
 
 
 
10. Spino-tectal tract.
 
 
 
11. Superficial arcuate tract.
 
 
 
12. Deep arcuate tract.
 
 
 
13. Fillet (lemniscus).
 
 
 
14. Vestibulo-spinal tract.
 
 
 
15. Olivo-cerebellar tract.
 
 
 
The pyramid of either side and the decussation of the pyramids
 
rave been already described. It may, however, be again stated
 
Fat the path of their motor nerve-fibres is downwards into the spinal
 
:ord.
 
 
 
The pyramidal tract has descended from the pons.
 
 
 
Posterior (or Direct) Spino-cerebellar Tract. —This tract extends
 
upwards from the lateral column of the spinal cord. It traverses
 
:he lower part of the lateral area of the bulb nearly as high as the
 
ower part of the olive, and immediately anterior to the tuberculum
 
^elatinosum, after which it passes backwards and upwards into the
 
inferior peduncle, of which it forms a part (Fig. 883).
 
 
 
Anterior Spino-cerebellar Tract. —This tract, like the dorsal or
 
lirect spino-cerebellar tract, extends upwards from the lateral column
 
if the spinal cord. It is situated chiefly on the dorsal aspect of the
 
ilive, but some of its fibres appear close to the outer side of that
 
body. Whilst the dorsal spino-cerebellar tract passes into the restiform body, and so reaches the cerebellar hemisphere directly, the ventral
 
spino-cerebellar tract is continued upwards into and beyond the pons
 
before reaching the cerebellar hemisphere.
 
 
 
Restiform Body.— The restiform body, or inferior peduncle of the
 
cerebellum, is situated on the dorsal aspect of the bulb in its upper
 
ir open part, the funiculus gracilis and funiculus cuneatus occupying
 
the dorsal aspect in its lower or closed part. It succeeds to the clava
 
ind cuneate tubercle, in which these two funiculi respectively end,
 
but it receives no nerve-fibres from the funiculi. It makes its first
 
appearance in relation to the nucleus cuneatus, and above the cuneate
 
tubercle it is a conspicuous massive bundle, which forms the lateral
 
boundary of the lower or bulbar half of the floor of the fourth ventricle.
 
Its course is upwards, outwards, and then suddenly backwards. It
 
sinks into the corresponding hemisphere of the cerebellum.
 
 
 
This peduncle is composed of fibres which are derived from the
 
 
 
following sources:
 
 
 
1. The olivo-cerebellar fibres of the inferior olivary nucleus of the opposite
 
 
 
side
 
 
 
2. The posterior cerebellar tract of the lateral column of the spinal cord of
 
 
 
the same side.
 
 
 
 
 
* 4^4
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
3. The anterior superficial arcuate fibres from the nucleus gracilis and
 
 
 
nucleus cuneatus of the opposite side.
 
 
 
4. The posterior arcuate fibres from the nucleus gracilis and nucleus
 
 
 
cuneatus of the same side.
 
 
 
5. Vestibular fibres from the vestibular nuclei of the vestibular division of
 
 
 
the auditory nerve.
 
 
 
The restiform body, from its composition, serves as an important
 
means of connection between the cerebellar hemisphere superiorly
 
and the medulla oblongata and spinal cord inferiorly.
 
 
 
Funiculus Cuneatus and Funiculus Gracilis. —These tracts are
 
prolonged upwards from the posterior column of the spinal cord.
 
As stated, each contains a grey nucleus, around the cells of which
 
the corresponding sensory nerve-fibres terminate at intervals as
 
they ascend. Towards the clava and cuneate tubercle the fibres
 
become few and are spread over the clava and cuneate tubercle,
 
finally ending in connection with the cells of the grey nuclei which
 
give rise to these prominences (Fig. 885).
 
 
 
Posterior Longitudinal Bundle. —The fibres of this bundle ( fasciculus
 
longitudinalis medialis ), when followed downwards into the anterior
 
column of the spinal cord on the same side, represent the fibres of the
 
ventral intersegmental tract. As these fibres are followed into the
 
lower part of the bulb they form a bundle, which lies close to the
 
median raphe and directly dorsal to the corresponding pyramid. This
 
strand represents the longitudinal bundle in the lower part of the
 
bulb. The deep arcuate fibres, to be presently described, pass obliquely
 
through it to the median line, where they decussate with those of the
 
opposite side. This decussation takes place in the interval between
 
the right and left dorsal longitudinal bundles. Having now reached the
 
other side, the deep arcuate fibres take an upward course, close to the
 
median line, as the medial lemniscus. The dorsal longitudinal bundle
 
and fillet are therefore now closely related to one another in the lower
 
part of the bulb, both lying dorsal to the pyramid, the fillet lying close
 
to the raphe.
 
 
 
In the upper part of the bulb the two tracts become distinct. The
 
posterior longitudinal bundle is displaced dorsalwards during the
 
formation of the fillet, and it comes into contact with the grey matter
 
on the floor of the fourth ventricle, whilst the lemniscus lies on the
 
dorsal aspect of the pyramid.
 
 
 
The posterior longitudinal bundle is prolonged into the ventral
 
column of the spinal cord on the same side, where it is represented,
 
as has been said, by the ventral intersegmental fibres.
 
 
 
A ventral or anterior longitudinal bundle (tecto-spinal tract) is described as
 
lyi n g on the ventral aspect of the dorsal or posterior longitudinal bundle. This
 
bundle, however, is not well defined. It descends into the anterior column of
 
the spinal cord, and is accompanied by the ponto-spinal tract, the fibres of which
 
spring from the cells of the formatio reticularis of the pons.
 
 
 
Arcuate Tracts. —These tracts form two goups—superficial and
 
deep.
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1465
 
 
 
 
 
The superficial arcuate fibres are arranged in two sets—anterior
 
md posterior.
 
 
 
The anterior superficial arcuate fibres arise from the nucleus gracilis
 
and nucleus cuneatus of the opposite side, and a few arise from the
 
arcuate nucleus of the same side. At the median line they decussate
 
with those of the opposite side, and emerge at the ventral median
 
fissure, where many of them arch over the medial and ventral
 
aspects of the pyramid. Others pierce the pyramid, whilst some
 
emerge at the ventro-lateral. sulcus between the pyramid and olive.
 
The fibres now pass outwards and dorsalwards, some arching over
 
the lower part of the olive, and finally enter the restiform body.
 
 
 
The posterior superficial arcuate fibres arise from the nucleus gracilis
 
and nucleus cuneatus of the same side, and they enter the restiform
 
body also of the same side.
 
 
 
 
 
 
 
Trigem. N.
 
 
 
Oblique Fasc.
 
 
 
Facial N.
 
 
 
Aud. N.
 
Flocculus
 
 
 
Circumoliv. Fasc.
 
 
 
 
 
Basilar Groove
 
 
 
 
 
Pyramid
 
 
 
 
 
Fig. 890. —Front Aspect of Pons and Medulla, showing Oblique Fibres
 
 
 
of Pons and Arcuate Fibres on Medulla.
 
 
 
 
 
The deep arcuate fibres are disposed in two sets—lemniscal and
 
olivo-cerebellar. The lemniscal deep arcuate fibres arise from the
 
nucleus gracilis and nucleus cuneatus of the same side. They sweep
 
forwards and inwards (Fig. 889) towards the raphe, passing obliquely
 
through the dorsal longitudinal bundle. At the median line they
 
decussate with those of the opposite side above the level of the decussation of the pyramids. Having reached the opposite side, the
 
deep arcuate fibres change their course, and now pass upwards The
 
ascending tract thus formed constitutes the medial lemniscus (or
 
medial fillet).
 
 
 
The decussation which takes place between the deep arcuate
 
fibres in the median line, immediately above the. decussation of the
 
pyramids, is called the decussation of . the lemnisci (decussatio lemmscorum), or the superior sensory decussation, as distinguished from
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1466
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
the inferior sensory or spino-thalamic decussation, which takes place
 
in the spinal cord.
 
 
 
The olivo-cerebellar deep arcuate fibres arise from the inferior olivary
 
nucleus of one side. Emerging through the hilum, they pass across
 
the median line to the opposite side. They then pass over or through
 
the inferior olivary nucleus of that side, on the dorsal aspect of which
 
they are collected into a distinct tract. This tract, arching backwards,
 
applies itself to the restiform body on its deep aspect, and is thereby
 
conducted to the cerebellar hemisphere. Its fibres terminate in the
 
cortex of the vermis and cerebellar hemisphere. The olivo-cerebellar
 
arcuate fibres constitute the olivo-cerebellar tract, which connects the
 
inferior olivary nucleus of one side with the cerebellar hemisphere of
 
the opposite side.
 
 
 
Lemniscus. —The lemniscus (or fillet), as seen in the bulb, is a wellmarked tract of fibres which lies on the dorsal aspect of the pyramid
 
close to the raphe. As just stated, its fibres are derived from the
 
lemniscal deep arcuate fibres of the opposite side. In the lower part
 
of the bulb the fillet and posterior longitudinal bundle are closely
 
related. In the upper part of the bulb, however, as already said,
 
the posterior longitudinal bundle is displaced dorsalwards by the
 
developing fillet, and the fillet, now distinct from the longitudinal
 
bundle, lies on the ventral aspect of that bundle, and on the dorsal
 
aspect of the pyramid. The ventral region of the bulb is thus traversed
 
by four longitudinal tracts, all of which lie close to the median line.
 
These tracts are related to each other in the following order from
 
before backwards (ventro-dorsally):
 
 
 
Pyramid.
 
 
 
Fillet.
 
 
 
Tecto-spinal.
 
 
 
Posterior longitudinal bundle.
 
 
 
Olivo-cerebellar Tract.— This tract has already been described in
 
connection with the olivo-cerebellar deep arcuate fibres.
 
 
 
Raphe of the Medulla Oblongata. —The raphe of the bulb occupies
 
the median plane above the decussation of the pyramids, and is
 
composed of fibres which, for the most part, cross obliquely from
 
one side to the other. These fibres represent (1) the anterior superficial
 
arcuate fibres, (2) the lemniscal deep arcuate fibres, and (3) the olivocerebellar deep arcuate fibres. A few fibres pass ventro-dorsally, and
 
some are disposed longitudinally. The fibres are therefore arranged
 
in an intersecting manner.
 
 
 
Central Canal of the Medulla Oblongata. —The central canal of the
 
spinal cord is prolonged upwards through the lower or closed part
 
of the bulb. As it ascends it is gradually displaced backwards, first
 
by the decussation of the pyramids, and afterwards by the decussation of the lemnisci. It is surrounded by a thick layer of grey matter,
 
which is derived from the basal portions of the ventral and dorsal
 
grey horns of the spinal cord, Superiorly, at the level of the obex,
 
 
 
 
 
/
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1467
 
 
 
 
 
it opens into the lower part of the fourth ventricle in the angle between
 
the two diverging clavse. The grey matter which surrounds the canal
 
is now spread out, and forms a thick covering over the lower part
 
of the ventricular floor, as has been said already.
 
 
 
Areas of Flechsig. —These areas involve the whole substance of the bulb,
 
and are mapped out by the funiculi of the hypoglossal and vagus nerves. Seen
 
in transverse section, these funiculi lie near each other as they arise from their
 
nuclei in the grey matter of the lower part of the floor of the fourth ventricle.
 
As the funiculi of the hypoglossal nerve pass forwards and those of the vagus
 
nerve outwards they diverge from each other, and the substance of the bulb
 
is thereby divided into three segments, which constitute the areas of Flechsig —
 
ventral, lateral, and dorsal (see Fig. 891).
 
 
 
 
 
 
 
Fig. 891. —Plan to illustrate the Three Areas of Flechsig, showing the
 
 
 
Main Structures in Each of These.
 
 
 
 
 
The ventral area lies between the raphe of the bulb and the funiculi of the
 
hypoglossal nerve. Throughout its thickness this area contains the following
 
structures:
 
 
 
The pyramid and arcuate nucleus (Fig. 891, P).
 
 
 
The lemniscus, decussating (L).
 
 
 
The posterior longitudinal bundle (B).
 
 
 
The formatio reticularis alba.
 
 
 
The lateral area lies between the funiculi of the hypoglossal nerve and those
 
of the vagus nerve. Throughout its thickness this area contains the following
 
structures:
 
 
 
The olive and inferior olivary nucleus.
 
 
 
The nucleus lateralis (NL).
 
 
 
The nucleus ambiguus (to be afterwards described) (NA).
 
 
 
The formatio reticularis grisea.
 
 
 
The dorsal area is the region behind the funiculi of the vagus nerve. Throughout its thickness this area contains the following structures:
 
 
 
The inferior peduncle.
 
 
 
The upper part of the cuneate nucleus (C).
 
 
 
The descending root of the vestibular nerve ^ 'po be afterwards
 
 
 
The fasciculus solitarius (S) \ described.
 
 
 
The spinal root of the fifth cranial nerve (V) )
 
 
 
The substantia gelatinosa (G).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1468 A MANUAL OF ANATOMY
 
 
 
Course of Chief Nerve Funiculi of Spinal Cord through Medulla Oblongata.
 
Spinal Cord. Medulla Oblongata.
 
 
 
Posterior Column.
 
 
 
Column of Goll (fasciculus gracilis).
 
 
 
Column of Burdach (fasciculus
 
cuneatus).
 
 
 
Lateral Column.
 
 
 
(Crossed) lateral cerebro-spinal tract.
 
 
 
Anterior cerebro-spinal tract.
 
 
 
Dorsal (or direct) spino - cerebellar
 
tract.
 
 
 
Ventral (or indirect) spino-cerebellar
 
(tract of Gowers).
 
 
 
Prepyramidal or rubro-spinal tract.
 
 
 
Lateral intersegmental.
 
 
 
Anterior Column.
 
 
 
Anterior cerebro-spinal tract.
 
 
 
Tecto-spinal tract.
 
 
 
Ventral intersegmental.
 
 
 
Anterior marginal bundle (of Lowenthal).
 
 
 
Development of Medulla Oblongata.— The bulb is developed from
 
the myelencephalon, which is the caudal division of the rhombencephalon.
 
 
 
2. The Pons.
 
 
 
The pons (Varolii) is situated above the medulla oblongata, and
 
between the hemispheres of the cerebellum. With the exception
 
of the inferior peduncles, all parts of the medulla oblongata are
 
prolonged into it. The pons presents two surfaces (ventral and
 
dorsal) and two borders (upper and lower). The ventral surface
 
(Fig. 890) rests upon the upper part of the basilar groove of the occipital
 
bone and the dorsum sellae of the sphenoid. It is convex from side to
 
side, and from above downwards, and has a transversely striated
 
appearance, due to the disposition of its superficial fibres. Along
 
the median line it presents the basilar groove, which extends from
 
the lower to the upper border, and lodges the basilar artery. On
 
either side of this groove the ventral surface is rendered prominent
 
by the prolongation upwards of the pyramids of the medulla oblongata, and the basilar groove is chiefly due to this circumstance. The
 
sensory and motor roots of the fifth nerve, lying close together, appear
 
on the lateral aspect of the ventral surface, the small motor root
 
being the upper of the two. The portion external to these two nerveroots constitutes the middle peduncle of the cerebellum. It is composed of the transverse fibres of the pons, which pass backwards and
 
laterally into the corresponding cerebellar hemisphere.
 
 
 
 
 
Funiculus gracilis and nucleus
 
 
 
gracilis.
 
 
 
Funiculus cuneatus and nucleus
 
 
 
cuneatus.
 
 
 
 
 
Inner three - quarters of opposite
 
pyramid.
 
 
 
Outer one-quarter of pyramid of
 
same side.
 
 
 
Lateral area below olive, and inferior
 
peduncle.
 
 
 
Lateral area below olive, and formatio reticularis.
 
 
 
 
 
Outer one-quarter of pyramid of
 
same side.
 
 
 
Posterior longitudinal bundle.
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1469
 
 
 
 
 
The dorsal surface is directed towards the cerebellum. It presents a triangular area which is covered with grey matter. This
 
area is continuous with the dorsal surface of the upper or open part of
 
the medulla oblongata, and it forms the upper or pontine part of the
 
floor of the fourth ventricle. On either side it is bounded by the
 
superior peduncle of the cerebellum as it passes upwards and inwards.
 
 
 
The upper border is slightly depressed at the centre, and on either
 
side of the median depression it slopes outwards and downwards
 
towards the middle peduncle of the cerebellum. The crura cerebri,
 
right and left, sink into the pons at the upper border.
 
 
 
 
 
 
 
Internal Structure of the Pons. —dhe pons is composed of a large
 
ventral and a small dorsal part.
 
 
 
Ventral Part.— This portion consists of (1) bundles of transverse
 
fibres, (2) bundles of longitudinal fibres, and (3) a large amount ot
 
 
 
 
 
grey matter. , , ,, £ •
 
 
 
The bundles of transverse fibres intersect the bundles of longitudinal fibres, and on either side they are collected into e mi e
 
peduncle of the cerebellum, which enters the corresponding cerebellar hemisphere. Some of the transverse fibres arise in, e cot ex
 
of the cerebellum as the axons of the cells of Purkinje, an 1
 
terminate in the pons in arborizations round the cells of the nucleus
 
pontis, mostly on the opposite side to that on which they arise
 
Other transverse fibres arise in the pons as the axons of of the nucleus pontis on one side. They then cross to the other
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
I 47 °
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Corpora Mamillaria
 
 
 
 
 
side, and enter the cerebellar hemisphere of that side, where they
 
terminate in arborizations in the cortex. The fibres, therefore, of
 
which the middle peduncle of the cerebellum is composed may be
 
regarded as being of two kinds—namely, efferent and afferent. The
 
efferent fibres arise in the cerebellar cortex and terminate in the
 
pons, whilst the afferent fibres arise in the pons and terminate in the
 
cerebellar cortex.
 
 
 
The bundles of longitudinal fibres in each half of the ventral part
 
of the pons are derived from the breaking up of the crusta or basis
 
 
 
pedunculi of the corresponding crus cerebri, which enters
 
the pons at its upper border.
 
Most of these bundles are
 
collected together at the
 
lower border of the pons,
 
and form the pyramid of the
 
medulla oblongata on the
 
same side. Certain of the
 
fibres of the basis pedunculi,
 
however, terminate in the
 
pons as follows: (i) some end
 
in arborizations around the
 
cells of the motor nucleus of
 
the fifth cranial nerve, the
 
nucleus of the sixth cranial
 
nerve, and the nucleus of the
 
seventh cranial or facial
 
nerve ; and (2) others end
 
in arborizations around the
 
 
 
 
 
Basis Pedunculi Cerebri --* 31 ;
 
Locus Perforatus Posterior
 
 
 
 
 
Right Pyramidal
 
Tract
 
 
 
Transverse Fibres
 
of Pons
 
 
 
Middle Peduncle of
 
Cerebellum
 
 
 
 
 
 
 
minL
 
 
 
Decussation of the Pyramids Ard :
 
 
 
■ f
 
 
 
Fig. 893.—Dissection of the Pons, showing the Course of the Pyramidal
 
Tracts of the Medulla Oblongata
 
(Hirschfeld and Leveille).
 
 
 
P., right pyramid; O.B., right olivary body.
 
 
 
 
 
cells of the nucleus pontis, all of the same side.
 
 
 
 
 
The fibres to cranial motor nuclei may run a more aberrant
 
course, leaving the basis pedunculi in the mid-brain and running
 
in the tegmentum of the pons to decussate and reach their
 
objectives. Some also run a recurrent course, leaving the pyramid
 
below the pons and turning upwards deeply.
 
 
 
The grey matter of the pons, which is large in amount, occupies
 
the intervals between the intersecting transverse and longitudinal
 
bundles, and contains small multipolar nerve-cells. It is known as
 
the nucleus pontis, and is continuous with the arcuate nuclei of the
 
medulla oblongata.
 
 
 
Corpus Trapezoides or Trapezium. —The trapezium is a fairly thick
 
layer of transverse fibres on either side, which have no connection
 
with the corresponding middle peduncle of the cerebellum. The
 
fibres are situated in the lower part of the pons dorsal to the pyramidal bundles. Within the trapezium are large multipolar cells,
 
which constitute the nucleus of the trapezium. The fibres of the
 
trapezium arise chiefly as the axons of the cells of the ventral cochlear
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1471
 
 
 
 
 
mcleus, and also of the dorsal cochlear nucleus (or tuberculum
 
icusticum), in which nuclei the fibres of the cochlear division of the
 
mditory nerve terminate, Some of the fibres arise from the superior
 
)livary nucleus; others are the axons of the cells of the nucleus of
 
;he trapezium; whilst a third set (auditory strice) arise from the
 
:uberculum acusticum of the opposite side. Certain of the fibres
 
 
 
 
 
 
 
Fig 8q4—Vertical Transverse Section through the Upper Part of
 
the Pons and Fourth Ventricle (from L. Testut’s ‘ Anatomie
 
Humaine,’ after Stilling).
 
 
 
 
 
1. Fourth Ventricle
 
 
 
2. Superior Velum
 
 
 
3. Superior Root of Fifth Nerve
 
 
 
4. Nerve-cells which accompany this Root
 
 
 
5. Posterior Longitudinal Bundle
 
 
 
6. Formatio Reticularis
 
 
 
7. Lateral Fissure of Isthmus
 
 
 
 
 
8. Section of Superior Cerebellar Peduncle
 
9,9. Medial and Lateral Portions of the
 
Lemniscus
 
 
 
10, 10. Transverse Fibres of the Pons
 
 
 
11, 11. Longitudinal Fibres of the Pons
 
 
 
12. Raph6
 
 
 
V. Fifth Nerve
 
 
 
 
 
: the trapezium terminate in the superior olivary nucleus, but the
 
laioritv cross the median plane, where they decussate with those
 
E the opposite side. Having crossed to the opposite side, they
 
ecome longitudinal, and form a well-marked ascending tract in the
 
orsal part of the pons, called the lateral lemniscus, which lies on the
 
 
 
uter side of the main or medial fillet. . ,
 
 
 
Dorsal or Tegmental Part of the Pons.— This portion is divided
 
ito two symmetrical halves by a median raphe, which is continuous
 
ith that of the upper or open part of the medulla oblongata It
 
insists of formatio reticularis, which is continued upwards from
 
re formatio reticularis of the bulb. The formatio reticularis of the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1472
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
dorsal part of the pons contains certain tracts of nerve-fibres and
 
nuclei, with which important nerves are connected. These are so
 
complicated that it is convenient to divide the dorsal part of the pons
 
into two regions—lower and upper.
 
 
 
Lower Region. —This region corresponds to the level of the trapezium in the ventral part of the pons, and succeeds the upper end of
 
the bulb. The inferior peduncle of the bulb lies for a short distance
 
on the lateral aspect of this region, but soon passes backwards and sinks
 
into the hemisphere of the cerebellum.
 
 
 
The tracts and nuclei of the formatio reticularis of the lower region,
 
which will be described in this place, are as follows:
 
 
 
1. Spinal sensory root of the fifth cranial nerve.
 
 
 
2. Motor nucleus of the facial nerve.
 
 
 
3. Superior olivary nucleus.
 
 
 
4. Nucleus of the sixth cranial nerve.
 
 
 
5. Posterior longitudinal bundle.
 
 
 
6. Rubro-spinal tract.
 
 
 
7. Tecto-spinal tract.
 
 
 
8. Lemniscus.
 
 
 
The funiculi of the spinal or descending sensory root of the fifth
 
cranial nerve appear ventro-medial to the mass of the inferior cere
 
 
 
Sixth Nucleus
 
 
 
 
 
Post. Long. Bundle
 
Facial Nucleus
 
 
 
Corp. Trapez.
 
 
 
 
 
Basis Pontis
 
 
 
 
 
Fig. 895.—Nuclear Positions in Pons (Schematic).
 
 
 
bellar peduncle. Close to the inner side of this root, and accompanying it
 
in its downward course, there is the inferior sensory nucleus of the fifth
 
nerve, around the cells of which the fibres of the spinal or descending
 
root of that nerve terminate at intervals. The inferior sensory nucleus
 
is an upward prolongation of the substantia gelatinosa, and interiorly it
 
extends to about the level of the second cervical spinal nerve (see Fig. 885).
 
 
 
The motor nucleus of the facial nerve is internal to the funiculi
 
of the spinal root of the fifth nerve. It lies deeply in the lower region
 
of the dorsal part of the pons on the dorsal aspect of the superior
 
 
 
 
 
 
 
Sensory Nucl. N.V.
 
Motor Nucl. V.
 
 
 
Superior Olive
 
Fifth Nerve
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1473
 
 
 
 
 
•livary nucleus. The motor fibres of the facial nerve arise as the
 
xons of the cells of this nucleus (see Fig. 896).
 
 
 
The superior olivary nucleus is situated on the ventral aspect of
 
he facial nucleus, and is close to the lateral part of the trapezium,
 
he fibres of which arch round its ventro-lateral aspect. Some of
 
hese fibres terminate in the superior olivary nucleus, whilst others
 
.rise from its cells.
 
 
 
In connection with the superior olivary nucleus three other nuclei are
 
lescribed: (1) an accessory superior olivary nucleus on the medial side of the
 
)rincipal nucleus; (2) a lateral pre-olivary nucleus on the ventral aspect of the
 
>rincipal nucleus; and (3) a medial pre-olivary nucleus on the ventral aspect of
 
he nucleus of the trapezium.
 
 
 
The nucleus of the sixth cranial nerve lies immediately beneath
 
he grey matter of the pontine part of the floor of the fourth ventricle,
 
ind on the lateral side of the dorsal longitudinal bundle which separates
 
he nucleus from the median raphe. It corresponds to that portion
 
 
 
 
 
supC- cerebellar
 
peduncle.
 
 
 
 
 
facial colliculus _ _
 
 
 
nucleus of--.,
 
sixth H.
 
 
 
post- longitudbundie.
 
 
 
stalk of olive"'
 
 
 
median lemniscus
 
 
 
 
 
 
 
inferior! cerebellar
 
middle j peduncle.
 
 
 
_\jai- vestibular
 
 
 
> x \ nucleus.
 
 
 
TV 7- 5 pinai root of V*- h n.
 
facial nucleus
 
 
 
 
 
-facial nerve
 
 
 
^vestibular part
 
""'of 8th nerve.
 
 
 
. "''Corpus trapezoides
 
 
 
""Supr- olivary nucleus
 
 
 
' oibducens nerve
 
 
 
pyramidal tract.
 
 
 
Fig. 896.—Diagrammatic Section through the Pons, to show Deep
 
Origins of Sixth (Red) and Seventh (Black) Cranial Nerves.
 
 
 
 
 
f the facial colliculus which lies on the pontine part of the floor of
 
he fourth ventricle directly above the auditory striae.
 
 
 
The medial or posterior longitudinal bundle lies close to the median
 
iphe, and on the medial side of the nucleus of the sixth nerve. Like
 
bat nucleus, it lies immediately beneath the grey matter of the pontine
 
 
 
art of the floor of the fourth ventricle. . , „
 
 
 
The lemniscus (medial, medial fillet) lies, as it <loes in the bulb,
 
entral to the dorsal longitudinal bundle, but m the dorsal part of tl e
 
ons the two strands are separated by a distinct interval occupied
 
 
 
93
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
*474
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
by the rubro- and tecto-spinal tracts. It will have been noticed tha J
 
in the spinal cord the tecto-spinal tract lies ventral to the rubro-spinal
 
but later on it will be seen that the tectum or quadrigeminal region i:
 
dorsal to the red nucleus. It is therefore clear that somewhere ir
 
their course they must reverse their relative positions, and the rubro
 
spinal become ventral to the tecto-spinal. Where this happens i:
 
not at present clear; indeed, the exact relations of these and man}
 
other tracts, such as the vestibulo-spinal, spino-thalamic, and spino
 
tectal in the upper part of their course, are still under investigation
 
The lemniscus occupies a broad area in that portion of the lowei
 
region of the dorsal part of the pons which is contiguous to the ventra
 
part. The area extends outwards from the median raphe.
 
 
 
Upper Region of the Dorsal Part of the Pons. —This region lies abovt
 
the level of the trapezium in the ventral part of the pons. The tracts
 
and nuclei of this region, which will be described in this place, are as
 
follows:
 
 
 
1. Superior peduncle of the cerebellum.
 
 
 
2. Nuclei of the fifth cranial nerve.
 
 
 
3. Medial or posterior longitudinal bundle.
 
 
 
4. Medial fillet or lemniscus.
 
 
 
5. Lateral fillet or lemniscus.
 
 
 
The superior peduncle of the cerebellum, after emerging from the
 
corresponding cerebellar hemisphere, lies on the lateral aspect of this
 
region, where it forms the lateral boundary of the upper or pontine pari
 
of the floor of the fourth ventricle. Its dorsal aspect is connected with
 
that of its fellow of the opposite side by the superior medullary velum l
 
and ventrally it sinks into the upper region of the dorsal part of the pons.
 
 
 
The pontine nuclei of the fifth cranial nerve are motor and sensory.
 
The motor and main sensory roots are pontine, and the sensory root is
 
prolonged down as the spinal tract, and up as the mesencephalic root.
 
 
 
The motor nucleus is situated close to the superior peduncle of the
 
cerebellum at the lower part of the lateral margin of the upper or
 
pontine part of the fourth ventricle. It lies near the surface, and the
 
axons of its cells form many of the fibres of the motor root of the nerve.
 
 
 
The main sensory nucleus is situated deeply on the outer side of
 
the motor nucleus, and on the ventral aspect of the superior peduncle
 
of the cerebellum. Some of the fibres of the sensory root ascend and
 
terminate in arborizations around the cells of this nucleus.
 
 
 
The lower or spinal sensory nucleus succeeds to the main sensory
 
nucleus, and is a continuation upwards of the substantia gelatinosa.
 
It is elongated, and extends into the upper part of the spinal cord to
 
about the level of the second cervical nerve. It lies on the medial
 
side of the spinal or descending sensory root of the fifth nerve, and
 
the fibres of that root (. spinal tract) terminate at intervals in arborizations
 
around its cells.
 
 
 
The mesencephalic root arises from groups of small cells which
 
are placed in the grey matter of the mid-brain, beside the aqueduct,
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1475
 
 
 
extending up as far as the canal of the lower end of the superior
 
:olliculus. Fibres run down from this part, but their actual disposition
 
n the fifth nerve is not yet settled.
 
 
 
There is some ground for supposing that this part of the nuclear
 
arrangement of the fifth nerve is concerned with the reception
 
of proprioceptive impulses from orbital muscles.
 
 
 
The posterior or medial longitudinal bundle has the same position
 
in the upper region as it has in the lower region. It lies close to the
 
median raphe, and immediately below the grey matter of the corresponding part of the floor of the fourth ventricle.
 
 
 
The main or medial lemniscus, like the main fillet in the lower
 
region, lies in that portion of the upper region of the dorsal part of the
 
pons which is near the ventral part, and it forms a layer of some breadth,
 
extending outwards from the median raphe.
 
 
 
The lateral lemniscus is a strand of fibres which lies on the outer side
 
of the medial fillet, and connects the cochlear nucleus with the opposite
 
inferior corpus quadrigeminum. Associated with the lateral fillet,
 
and lying between it and the medial fillet, there is a collection of nervecelis, called the nucleus of the lateral lemniscus.
 
 
 
Development of the Pons. —The pons is developed from the ventral and lateral
 
walls of the metencephalon, which is one of the divisions of the rhombencephalon. The nuclear matter seems to be derived from the ponto-bulbar body,
 
spreading over the surface of the neural tube.
 
 
 
3. The Cerebellum.
 
 
 
The cerebellum, or small brain, occupies the inferior occipital or
 
cerebellar fossae of the occipital bone. It lies beneath the posterior
 
parts of the hemispheres of the cerebrum, from which it is separated
 
by a septum of the dura mater, called the tentorium cerebelli, and it is
 
behind and above the medulla oblongata and pons. It is composed
 
of white and grey matter, the white matter being situated in the
 
interior, where it constitutes the medullary substance, and the grey
 
matter being spread over the surface of the cortex. In appearance it
 
is laminated or foliated, the laminae being separated from each other
 
by parallel, slightly curved sulci. It is composed of two large lateral
 
portions, called hemispheres, and a connecting median portion, termed
 
the vermis, these parts being much more distinct below than above.
 
When looked at from above it presents in the median line two notches,
 
anterior and posterior. The anterior notch, which is wide, is known
 
as the incisura semilunaris , and it contains the inferior pair of quadrigeminal bodies and the superior cerebellar peduncles. The posterior
 
notch is narrow, and is occupied by the falx cerebelli. The most
 
conspicuous sulcus of the cerebellum is the great horizontal fissure,
 
which extends round the circumference, and passes for some distance
 
into the interior. By means of this fissure the cerebellum is divided
 
into two parts, upper and lower.
 
 
 
Relatively smaller in the new-born child, the cerebellum forms
 
in the adult about an eighth of the whole mass of the brain.
 
 
 
 
 
 
 
I 47^
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
The cerebellar surface is marked, as stated above, by the presence
 
of numerous flattened or laminar gyri or folds, each fold being separatee
 
from its neighbours by sulci of appreciable depth. Among these
 
fissures are certain ones which are evident and deeper, and these car
 
be taken to divide the surfaces into lobules or parts, which have some
 
small descriptive value.
 
 
 
 
 
The presence of the foliated surface, and of certain striking
 
appearances in different parts of the cerebellum, have led in the
 
past to a wealth of terminology and description which, for the
 
greater part, does not seem to be of much value or utility.
 
Moreover, since these terms have in many instances come dowr
 
from long past periods, they are archaic and fanciful. Thus it
 
seems desirable to replace these with a short account of the
 
cerebellar surface, broadly described, after which the older terms
 
 
 
 
 
Anterior Notch
 
(Incisura Semilunaris)
 
 
 
Central Lobule
 
 
 
Anterior Crescentic Lobule
 
 
 
/
 
 
 
Primary Fissure
 
 
 
Posterior Crescentic
 
Lobule
 
 
 
 
 
Postero-superior
 
Fissure
 
 
 
 
 
f;A^SL Cor P° ,a Q ua drigemina
 
 
 
 
 
Postero-superior
 
 
 
Lobule
 
 
 
 
 
 
 
-Culmen Monticuli
 
 
 
 
 
.Preclival Fissure
 
 
 
 
 
Postclival Fissure
 
 
 
 
 
Postero-inferior Lobule
 
 
 
 
 
Clivus Monticuli
 
 
 
 
 
Posterior Notch Folium Cacuminis
 
 
 
 
 
Fig. 897.—The Cerebellum (Superior View).
 
 
 
 
 
and descriptions will be given in small print, for purposes of
 
reference if required. Subsequently a short morphological consideration of the part can be added.
 
 
 
Upper Surface of the Cerebellum. —This surface presents in the
 
median line the upper part of the vermis, known as the superior vermis
 
(see Fig. 897). It extends from the incisura semilunaris to the posterior
 
notch, and it forms a laminated elevation, which is higher in front than
 
behind, the most prominent part being known as the monticulus cerebelli. On either side of the superior vermis the upper surface of each
 
hemisphere inclines downwards to the circumference, and there is no
 
distinct demarcation between it and the superior vermis.
 
 
 
This upper aspect is divided (Fig. 898) by two main fissures, primary
 
and postclival, which are continued across the slight elevation of the
 
superior vermis.
 
 
 
 
 
 
 
/
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
x 4 77
 
 
 
The primary fissure (Fig. 898, PR) cuts across the vermis a little
 
behind its highest point, the culmen. From this the fissure is continued
 
with a slight forward curve on each side, to reach the horizontal fissure.
 
 
 
The fissure is termed ‘ primary ’ because it forms the posterior
 
limit, at a fairly early stage, of the morphological entity, the
 
anterior lobe.
 
 
 
The postlunate or postclival fissure (PC) is behind the primary fissure
 
and below it; this is due to the descent of the vermis from the culmen,
 
forming its ‘ declive * behind the primary fissure. The postclival
 
fissure turns forward on each side with a bolder curve towards the
 
horizontal fissure.
 
 
 
 
 
 
 
Fig. 898. —Upper Aspect of Cerebellum, with Main Subdivisions.
 
 
 
C, culmen; D, declive (or clivus); PR, primary fissure; PC, postlunate (or postclival) fissure; H, posterior end of horizontal fissure.
 
 
 
The anterior lobe lies above and in front of the primary fissure, including the parts of the vermis and lateral lobes as a continuous whole.
 
 
 
The posterior lunate lobe lies between the primary and postlunate
 
fissures, and includes also the central vermis.
 
 
 
The posterior end of the horizontal sulcus (H) appears usually on
 
this aspect of the cerebellum. It fails to reach the vermis, usually
 
running into the postlunate sulcus.
 
 
 
The lobule which is seen on each side below the postlunate and
 
above the horizontal fissure is frequently referred to as the superior
 
crescentic lobule; it is also termed the superior (division of the) ansiform
 
lobe.
 
 
 
The superior vermis is composed of five lobules, named, in order from
 
before backwards, the lingula, central lobule, culmen monticuli, clivus
 
monticuli, and folium cacuminis. The lingula is deeply placed, and consists of about four laminae or folia, which lie over the superior medullary
 
 
 
 
 
 
 
 
 
[478
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
velum as it extends between the superior cerebellar peduncles. Its laminae
 
may be continued on either side over the superior cerebellar peduncle,
 
and, when this is so, the prolongation is known as the frenulum lingulae.
 
 
 
The central lobule is of small size, and lies at the bottom of the incisura
 
semilunaris. It is separated from the lingula by the precentral fissure,
 
and from the culmen monticuli by the postcentral fissure.
 
 
 
The culmen monticuli forms the summit of the superior vermis. It is
 
composed of several laminae, and posteriorly is separated from the clivus
 
by the preclival fissure.
 
 
 
The clivus monticuli represents the sloping part of the monticulus
 
cerebelii. It is situated behind the culmen monticuli, and is composed of
 
several laminae. Posteriorly it is separated from the folium cacuminis
 
by the postclival fissure.
 
 
 
The folium cacuminis forms the posterior extremity of the superior
 
vermis, and lies at the posterior notch, where it is placed above the great
 
horizontal fissure.
 
 
 
 
 
i locculus
 
 
 
 
 
Biventral Lobule
 
 
 
 
 
Lobulus Gracilis 1
 
Great Horizontal
 
 
 
Fissure , I
 
 
 
t
 
 
 
Inferior Semilunar Lobule
 
 
 
 
 
 
 
Amygdala (Tonsil)
 
 
 
 
 
Pyramid
 
Tuber Valvulae
 
 
 
 
 
-Pregracile
 
Fissure
 
— Mid-gracile
 
Fissure
 
—Post gracile
 
Fissure
 
-•-Small Horizontal
 
Fissure
 
 
 
 
 
Fig. 899.— The Cerebellum (Inferior View).
 
 
 
1 he inferior semilunar lobule and the lobulus gracilis constitute the postero
 
inferior lobule. Old terminology used.
 
 
 
 
 
The upper surface of each hemisphere is mapped out into lobules, which
 
are continuous with the subdivisions of the superior vermis, with the
 
exception of the lingula. These are called, in order from before backwards, the ala, anterior crescentic lobule, posterior crescentic lobule, and
 
postero-superior lobule.
 
 
 
The ala is continuous with the central lobule, from which it is prolonged
 
for a limited distance round the anterior part of the hemisphere in the
 
region of the incisura semilunaris.
 
 
 
The anterior crescentic lobule is continuous with the culmen monticuli,
 
and represents the anterior subdivision of the upper surface of the cerebellar
 
hemisphere. It is limited posteriorly by a curved sulcus, called the anterosuperior fissure, which is continuous with the preclival fissure (fissura prima),
 
and opens at the circumference into the great horizontal fissure. The
 
right and left anterior crescentic lobules, together with the culmen monticuli, form the lobus culminis (see Fig. 897).
 
 
 
The posterior crescentic lobule is continuous with the clivus monticuli.
 
It is limited in front by the antero-superior fissure, and behind by the
 
postero-superior fissure, the latter being continuous with the postclival
 
fissure, and opening at the circumference into the great horizontal fissure.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1479
 
 
 
 
 
The right and left posterior crescentic lobules, together with the clivus
 
monticuli, form the lobus clivi.
 
 
 
The postero-superior lobule (superior semilunar lobule) corresponds to,
 
but is much more extensive than, the folium cacuminis. It is limited
 
in front by the postero-superior fissure, and behind by the great horizontal
 
fissure. The right and left postero-superior lobules, together with the
 
folium cacuminis, form the lobus cacuminis.
 
 
 
Under Surface of the Cerebellum. —The under surface presents in
 
:he median line a deep groove, called the vallecula, which is continuous
 
Dehind with the posterior notch. Anteriorly it lodges the medulla
 
Dblongata, and lying in the bottom of it there is the lower part of the
 
/ermis, which is known as the inferior vermis. The vallecula separates
 
the two cerebellar hemispheres from each other, and the inferior vermis
 
s separated on either side from the corresponding hemisphere by a
 
furrow called the sulcus valleculce. The under surfaces of the hemi
 
 
 
 
 
Fig. 900.—Lower Aspect of Cerebellum, showing the (Inferior) Ansiform
 
Lobe and the Paramedian Lobule or Tonsil; also the Flocculus.
 
 
 
 
 
spheres are markedly convex, and are received into the inferior occipital
 
or cerebellar fossae of the occipital bone.
 
 
 
The inferior aspect of the cerebellum (Fig. 900) presents on the
 
lateral lobes, near the margins, the greater part of the horizontal
 
fissure (H). The two additional fissures shown in the figure are of quite
 
secondary importance; the upper one of the two was taken formerly
 
as the lower boundary of the ‘ inferior crescentic lobule (ISL.), but it
 
is not necessary now to subdivide the inferior surface in this way, but
 
rather to term all this curved surface the posterior or posteio-inferior
 
lobe, or the inferior (part of the) ansiform lobe. #
 
 
 
The paramedian lobule or tonsil, however, stands out as a striking
 
formation on each side of the ‘ posterior notch, and is not included in
 
the name given to the rest of the inferior surface. The base of the
 
tonsil is received in a cup-shaped concavity on the inferior and medial
 
surface of the ansiform lobe, from which it is separated by a
 
deep retrotonsillar fissure. The loosely foliated flocculus (FLOCC) is
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1480
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
visible on each side, outside and in front of the tonsil. The flocculus
 
has a white ' stalk/ which is continuous with the inferior medullary
 
vellum, making with this a large part of the bed of the hollow which
 
contains the tonsil. This velum is connected centrally with the
 
* nodule/ the terminal piece of the inferior vermis.
 
 
 
The inferior vermis is composed of four lobules, named, in order from
 
behind forwards, tuber valvulse, pyramid, uvula, and nodule.
 
 
 
The tuber valvulae (tuber posticum) forms the posterior part of the
 
inferior vermis, and is composed of several laminae. On either side it is
 
prolonged into the corresponding hemisphere, and becomes continuous
 
with the postero-inferior lobule. It is the only part of the inferior vermis
 
which is prolonged into the cerebellar hemispheres.
 
 
 
The pyramid is situated in front of the tuber valvulae. It presents about
 
four laminae, and is separated by deep sulci from the tuber valvulae behind
 
and the uvula in front, whilst on either side it is separated from the cerebellar hemispheres by the sulcus valleculae. Laterally it is connected
 
with the biventral lobule of the hemisphere by means of a faint ridge, but
 
this lies low in the sulcus valleculae as it crosses.
 
 
 
The uvula is situated in front of the pyramid, and between the amygdalae
 
or tonsils of the hemispheres. It is triangular, the base being directed
 
backwards, and it consists of several laminae. It is separated on either
 
side from the hemisphere by the sulcus valleculae. Laterally its narrow
 
part is connected with the amygdala by a ridge of grey matter, but this
 
lies low in the sulcus valleculae as it crosses. This ridge is notched at
 
intervals, and is called the furrowed band.
 
 
 
The nodule forms the anterior part of the inferior vermis, and is composed of several laminae, which are largely concealed by the uvula. It is
 
connected on either side with the flocculus by a thin semilunar band of
 
white matter, which is the lateral portion of the inferior medullary velum.
 
 
 
The fissures of the inferior vermis are three: postpyr amidal, between the
 
pyramid and the tuber valvulae; prepyramidal (fissura secunda), between
 
the pyramid and the uvula; and postnodular, between the nodule and the
 
uvula.
 
 
 
The under surface of each hemisphere is mapped out into four lobules,
 
which are called, from behind forwards, the postero-inferior lobule, the
 
biventral lobule, the amygdala, and the flocculus.
 
 
 
The postero-inferior lobule is situated at the back part of the under
 
surface of the hemisphere. It is divided into four curved parts by three
 
curved Assures. The anterior two parts are known as the lobulus gracilis,
 
and the posterior two as the inferior semilunar lobule. The right and left
 
postero-inferior lobules, together with the tuber valvulae, form the lobus
 
tuberis.
 
 
 
The biventral lobule is composed of curved laminae, and is somewhat
 
triangular. The pointed end is directed backwards and inwards, and it
 
is connected with the pyramid by a faint ridge, which lies low in the sulcus
 
valleculae. The base is directed forwards towards the flocculus. The
 
lobulus gracilis lies external to it, and the amygdala is on its inner side.
 
The biventral lobule is divided by a sulcus into two portions, outer and
 
inner; hence the name ‘ biventral.’ The right and left biventral lobules,
 
together with the pyramid, form the lobus pyramidis.
 
 
 
The amygdala (tonsil) forms a conspicuous prominence between the
 
uvula and the biventral lobule. It is situated in a depression of the
 
vallecula, which is known as the nidus avis (‘ bird’s nest ’), and its long axis
 
is almost sagittal. It is connected with the narrow part of the uvula by
 
the furrowed band in the sulcus valleculae. The right and left amygdalae,
 
together with the uvula, form the lobus uvulae.
 
 
 
The flocculus (subpeduncular lobule) is a small irregular lobule which
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1481
 
 
 
is situated between the front of the biventral lobule and the middle peduncle
 
of the cerebellum. Internally it is connected with the nodule by the lateral
 
portion of the inferior medullary velum. The right and left flocculi,
 
together with the nodule, form the lobus noduli.
 
 
 
In the foetus a structure, known as the paraflocculus, lies behind and to the
 
outer side of the flocculus, and occupies a depression in the petrous bone.
 
In the lower monkeys it persists throughout life, but in man it atrophies
 
after birth.
 
 
 
The fissures of the under surface of each hemisphere are: (1) a continuation of the postnodular sulcus, between the biventral lobule and the
 
flocculus; (2) a continuation of the prepyramidal sulcus, between the
 
am yfl ( lala an< d the biventral lobule; (3) the pregracile, or anterior arcuate
 
sulcus, between the biventral lobule and the lobulus gracilis; (4) the midgracile, or middle arcuate sulcus, within the lobulus gracilis; (5) the postgracile, or posterior arcuate sulcus, between the lobulus gracilis and the
 
inferior semilunar lobule; and (6) the small horizontal sulcus within the
 
inferior semilunar lobule.
 
 
 
Cerebellar Morphology.—Extensive examination of the types and
 
varieties of the cerebellum found in different classes of animals has
 
gradually established the fundamental parts of this organ. It has
 
)een shown to consist essentially of three lobes—anterior, middle, and
 
bosterior—of which the anterior is the most primitive, the middle and
 
posterior appearing in higher forms; in birds both these are present,
 
md in mammals reach a more extensive development, while in man
 
md the higher mammals the middle lobe reaches its most expanded
 
:orm, varying much in the different orders of mammals below these,
 
[t may be added that the vermis is to be looked on as a more primitive
 
md older part of the organ than the lateral lobes, in which the paired
 
donations exhibit much variety.
 
 
 
The anterior lobe is represented in man by that portion of the cerebellum lying above and in front of the primary fissure; this has received
 
ts name from this relationship, and various names have been given
 
:o the part thus marked off, known now as the anterior lobe. The
 
obe includes the vermis in this part, as far back as behind the culmen,
 
vhere the fissure cuts through it.
 
 
 
The middle lobe is a simple lens-shaped formation (Fig. 901 a), as
 
;een on the surface in lower vertebrates. In the mammals, however,
 
t is found to present a simple transverse bar immediately behind the
 
brimary fissure, but behind this it shows medial and lateral parts, of
 
vhich the lateral portions exhibit (Fig. 901 a) two main divisions—an
 
ipper or anterior one, curved on itself, and hence termed the ansiform
 
obule \ and a lower one (continuous with the ansiform lobule) placed
 
beside the median formations, and hence named the paramedian
 
obule.
 
 
 
The posterior lobe is also composed of a median part (posterior
 
nedian lobule) and two lateral portions; these consist on each side of
 
1 flocculus and paraflocculus, as illustrated in the figure.
 
 
 
The human cerebellum possesses a relatively simple anterior lobe,
 
is pointed out above. There is also a recognizable ‘ transverse bar,’
 
narking the upper portion of the middle lobe, in the so-called ‘ lobulus
 
Implex ' (posterior lunate lobe or posterior crescentic), which includes
 
 
 
 
 
1482
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
the central declive. It is behind this that the middle lobe is particularly
 
concerned in forming the greater part of the human lateral lobe from
 
the ansiform lobule on each side, while the posterior lobe remains
 
centrally, but degenerates in part in its lateral portions.
 
 
 
 
 
 
 
Fig. 901A.—Illustrations of Cerebellar Structural Morphology, based
 
 
 
on Figures by Ingvar.
 
 
 
1, higher reptile; 2, bird; 3, mammal; A, M, P, anterior, middle, and posterior
 
lobes; ANS, PM, ansiform and paramedian lobules; F, PF, flocculus and
 
paraflocculus.
 
 
 
The schematic drawings in Fig. 901B may make this transformation
 
clearer. In the first scheme the recognition of the fundamental parts,
 
as already described, is evident and straightforward; the anterior lobe
 
(A) is separated by the primary fissure from the ‘ lobulus simplex,'
 
marked by the upper M; the lower M indicates the lower portion of the
 
 
 
 
 
 
 
Fig. 901 b.— To illustrate Hypothetical Stages in the Evolution of
 
 
 
Form of Human Cerebellum.
 
 
 
(References as in previous figure.)
 
 
 
 
 
middle lobe, with its two lateral pieces consisting of ansiform (ANS)
 
and paramedian (PM) lobules. The overgrowth of the ansiform lobule
 
accounts for the greater part of the lateral lobe (behind the lobulus
 
simplex), as shown in the second figure, while the paramedian lobule
 
remains as the ‘ tonsil.' The great ansiform enlargement is naturally
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1483
 
 
 
in a doisal and lateral direction mainly, so that the paramedian lobule
 
is overlapped, and finds itself on the anterior aspect of the lower and
 
median part of the enlargement.
 
 
 
The posterior lobe, stippled, is seen (as in the primitive forms,
 
Fig. 901A) to have a central and two lateral pieces; these show floccular
 
(F) and parafloccular (PF) enlargements. In the human foetus these
 
ire represented, but the paraflocculus is lost, and the flocculus remains
 
done in the adult condition, connected still with the median part of the
 
posterior lobe.
 
 
 
When estimating the comparative values of the parts of the cerebellum, as above, it must be remembered that the growing thickness of
 
the organ affects not only the lateral, but also the median parts; thus,
 
the vermis is very thick in the middle lobe and fades rapidly in the
 
bosterior lobe, so that this last is turned down and comes to look
 
iownwards and forwards. 1 his is associated with the overgrowth
 
bf the ansiform lobule, whence the paramedian lobule is visible from
 
below and in front, and not from behind, as in the scheme; it is covered
 
behind by the increasing growth of the ansiform lobule extending
 
medially behind it and the buried posterior derivatives.
 
 
 
To sum up shortly: the lateral lobes of the cerebellum are, for
 
their posterior, lateral, and greater part, overgrowths of the
 
ansiform portion of the middle lobe, the tonsil being paramedian.
 
Above this is another part (lobulus simplex, upper crescentic) of
 
the middle lobe, separated by the primary fissure from the simple
 
anterior lobe, the oldest lobe of the organ. The vermis is represented in both anterior and middle lobes as the central portion,
 
thickened very much in these parts, but getting rapidly smaller
 
(and hence reversed, as it were) in the posterior lobe. The
 
flocculus is the remnant of the lateral portion of the posterior
 
lobe.
 
 
 
The vermis in front of the primary fissure is the central part of the
 
interior lobe, behind this fissure, down to and including the declive;
 
t belongs to the upper portion (lobulus simplex) of the middle lobe,
 
:he lower part of which includes the ‘ tuber vermis ' and ends at the
 
prepyramidal fissure/ The central part of the posterior lobe includes
 
:he pyramid, uvula, and nodule, and it is of interest to note that these
 
barts are particularly connected (Holmes and Stewart) with the medial
 
iccessory olive, the oldest part of the inferior olivary structures; the
 
arge inferior olive of higher mammals has appeared with the lateral
 
growth of the cerebellum in them, and in less direct connection with
 
:he development of the cerebral cortex.
 
 
 
Peduncles of the Cerebellum.—The peduncles are three in number
 
Dn either side—superior, middle, and inferior—and they are composed
 
bf fibres which enter or leave the central white medullary substance.
 
 
 
The superior peduncles (brachia conjunctiva) are largely composed
 
bf efferent fibres, and are at first concealed from view by the upper
 
br anterior portions of the hemispheres. After they leave the hemi
 
 
 
i 4 8 4
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
spheres they pass upwards on the lateral aspects of the dorsal surface
 
of the pons in a converging manner towards the quadrigeminal bodies
 
(or colliculi of mid-brain). They form the lateral boundaries of the
 
upper part of the floor of the fourth ventricle, and by their convergence
 
they project slightly over that part of the ventricle, so as to take part
 
in its roof. The superior medullary velum extends between the two
 
peduncles, and closes the interval between them. On reaching the
 
inferior pair of quadrigeminal bodies the two peduncles pass beneath
 
them and enter the mesencephalon, where their course will be subsequently described (see p. 1553). Most of the fibres of each superior
 
peduncle are derived from the corresponding nucleus dentatus, but a
 
few come from the grey matter of the cerebellar cortex. In addition
 
to these there are the fibres of the ventral (or indirect) cerebellar tract
 
(of Gowers).
 
 
 
The middle peduncles are of large size, and are formed by the transverse fibres of the pons, these being gathered together on either side
 
into a large bundle, which passes backwards and laterally into the
 
white central medullary substance of the corresponding hemisphere.
 
The fibres of each middle peduncle are both afferent and efferent. The
 
afferent fibres arise in the pons from the cells of the nucleus pontis of
 
the opposite side, and terminate in arborizations around the cells of the
 
cerebellar cortex. The efferent fibres arise from the cells of the cerebellar cortex of the same side, and terminate in arborizations around
 
the cells of the nucleus pontis, mostly on the opposite side.
 
 
 
The inferior peduncles are principally composed of afferent fibres,
 
which are derived chiefly from the dorsal (or direct) cerebellar tract
 
and the olivo-cerebellar tract of either side. The fibres of the dorsal
 
cerebellar tract terminate in the cortex of the superior vermis on both
 
sides of the median line. The fibres of the olivo-cerebellar tract , which
 
are derived from the inferior olivary nucleus of the medulla oblongata
 
on the opposite side, terminate in the cortex of the vermis and cerebellar
 
hemisphere. The superficial arcuate fibres, which form part of the
 
inferior peduncle, are connected with the cortex of the vermis and
 
cerebellar hemisphere. There are also fibres connecting the vermis
 
with the vestibular nerve, thus forming the direct sensory cerebellar
 
tract (see p. 1623).
 
 
 
It should be noted that the inferior peduncle comes up from below
 
to a position between the other two, the middle peduncle being external
 
and the superior internal. Having reached this position, the inferior
 
peduncle suddenly bends backwards and passes into the cerebellum.
 
 
 
White and Grey Matter of the Cerebellum.—In the hemispheres
 
and vermis the white matter is situated in the centre as the medulla,
 
and the grey matter is disposed superficially as the cortex. The
 
white matter in the interior of the vermis is occasionally termed the
 
corpus trapezoides. When sagittal sections of a hemisphere are made,
 
the mass of white matter in the centre is seen to send offshoots into
 
the lobules. From the sides of these offshoots secondary processes
 
are given off, and these in turn furnish tertiary processes, the white
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1485
 
 
 
latter in all cases being covered by grey matter. When the section
 
5 made across the direction of the laminae or folia the appearance
 
•resented is like the trunk and branches of a tree; hence the name
 
rbor vitce cerebelli is applied to it (see Fig. 902).
 
 
 
Nuclei.—The corpus dentatum (Fig. 902) is a collection of grey
 
latter which is situated within the white matter of each hemisphere,
 
nd is very like the inferior olivary nucleus in the olivary body of the
 
aedulla oblongata. It is composed
 
if a wavy grey lamina, disposed
 
n the form of a capsule, which
 
ncloses white matter. The capsule
 
>resents an opening or hilum at its
 
ipper and inner part, and through
 
his a large number of the fibres
 
>f the superior cerebellar peduncle
 
merge from the interior.
 
 
 
There are three other nuclei on
 
;ach side as follows: (1) the nucleus
 
imboliformis, close to the inner
 
;ide of the hilum of the corpus
 
lentatum; (2) the nucleus globosus,
 
nternal to the preceding ; and
 
3) the nucleus fastigii, or rooflucleus, situated in the vermis,
 
dose to the median line, and contiguous to its fellow of the opposite
 
dde.
 
 
 
Commissural and Association Fibres.—The commissural fibres pass
 
 
 
horn the white matter of one hemisphere to that of the opposite hemisphere. They traverse the vermis in two sets, superior and inferior.
 
Die association fibres are confined to each side, and they connect
 
idjacent laminae, passing across the bottom of the fissures which
 
separate them.
 
 
 
Medullary Vela.—These are thin laminae or curtains of white
 
matter, and are two in number, superior and inferior.
 
 
 
The superior medullary velum (or valve of Vieussens) is continuous
 
with the white matter of the vermis. It extends between the converging superior cerebellar peduncles, bridging over the interval between
 
them, and becoming continuous with their inner margins. Superiorly
 
it extends to the inferior pair of quadrigeminal bodies, and inferiorly
 
it passes into the corpus trapezoides or white matter of the vermis.
 
It forms a large portion of the roof of the upper part of the fourth
 
ventricle, and its dorsal surface supports the lingula of the superior
 
vermis. From the upper part of the superior medullary velum a
 
band of white fibres, called the frenulum veil, passes to the lower part
 
of the median longitudinal groove which separates the lateral pairs of
 
quadrigeminal bodies. Immediately below the inferior pair of quadrigeminal bodies the fourth pair of cranial nerves emerge from the
 
superior medullary velum on either side of the frenulum veli. The
 
 
 
 
 
 
 
Fig. 902.—Anteroposterior Section through Lateral Lobe,
 
showing Dentate Nucleus.
 
 
 
 
 
 
 
I486
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
tract of Gowers (ventral spino-cerebellar tract), after having traversed
 
the formatio reticularis of the medulla oblongata and the dorsal part
 
of the pons, passes into the superior medullary velum, and then descends in the superior cerebellar peduncle to the cerebellum.
 
 
 
The inferior or posterior medullary velum is a thin lamina of white
 
matter which consists of three parts—median and two lateral, right
 
and left.
 
 
 
The median part supports dorsally the nodule of the inferior
 
vermis. It is a prolongation of the white matter of the vermis, and
 
lies on the upper or ventral aspect of the nodule, to which it is adherent.
 
As it leaves the white matter it is contiguous to the superior medullary
 
velum, but the two laminae take different directions. As they diverge
 
they make the cerebellar recess or apex of the roof of the fourth ventricle.
 
 
 
 
 
Layer of Purkinje's Cells
 
 
 
 
 
 
 
Fia Mater
 
 
 
 
 
_ Molecular Layer
 
 
 
 
 
Granular Layer
 
 
 
 
 
White Medullary
 
Substance
 
 
 
 
 
Fig. 903. —Structure of a Lamina
 
■the Cerebellum (magnified).
 
 
 
 
 
of
 
 
 
 
 
The superior medullary velum
 
passes upwards between the
 
dorsal parts of the superior
 
peduncles of the cerebellum.
 
The median part of the inferior medullary velum passes
 
ventralwards and then downwards. It is succeeded in a
 
downward direction by the
 
ependymal epithelium and
 
pia mater (tela chorioidea
 
inferior), which form a large
 
portion of the lower part of
 
the roof of the fourth ventricle. The middle part of
 
the inferior medullary velum
 
forms the upper portion of
 
 
 
 
 
the lower part of the roof of the fourth ventricle.
 
 
 
Each lateral part of the inferior medullary velum extends laterally
 
to the corresponding flocculus in the form of a semilunar band. The
 
ventral surface of this band is directed towards the fourth ventricle,
 
and the dorsal surface is related to the amygdala or tonsil. One
 
border of the band is free and concave, whilst the other is continuous
 
with the white matter of the corresponding cerebellar hemisphere.
 
 
 
The inferior medullary velum forms a part of the lobns noduli, the
 
other parts being the nodule and the two flocculi.
 
 
 
 
 
Minute Structure of the Cerebellar Laminae. —Each lamina or folium of the
 
cerebellum consists of (1) a central part or core of white matter, which is an
 
offshoot from the white medullary substance; and (2) an external part or cortex
 
of grey matter.
 
 
 
Grey Cortex. —The grey cortex is composed of two layers, an outer molecular
 
layer and an inner granular layer. Between these two layers there is a stratum
 
of characteristic large cells, called the cells or corpuscles of Purkinje.
 
 
 
The cells of Purkinje are pyriform or flask-shaped, and are situated, as just
 
stated, between the molecular and granular layers. The narrow or superficial
 
end of each cell projects into the molecular layer, and the broad or deep end rests
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE NERVOUS SYSTEM
 
 
 
 
 
1487
 
 
 
 
 
1 the granular layer. From the broad or deep end of each cell a single axon
 
isses off, which enters the granular layer, where it soon becomes medullated,
 
id then forms a nerve-fibre of the white medullary substance. The axon of
 
urkinje’s cell gives off a few collateral recurrent branches, some of which end
 
1 the granular layer, whilst others enter the molecular layer.
 
 
 
From the narrow or superficial end of each cell one or two dendrons are given
 
ff. These divide and subdivide at frequent intervals in the molecular layer
 
like the antlers of a deer.' The dendritic processes so formed are arranged
 
1 an arborescent manner, and are distinct from those of adjacent cells. They
 
ermeate the molecular layer as far as the surface.
 
 
 
The molecular layer consists of a few nerve-cells and many nerve-fibres.
 
 
 
The nerve-cells are situated partly in the inner or deep portion of the
 
lolecular layer, and partly in its outer portion.
 
 
 
The inner cells are known as the basket-cells, and they lie in the vicinity of
 
tie cells of Purkinje. Each basket-cell has several dendritic processes which
 
imify in all directions. In addition to these processes there is an axon, which
 
prings from the side of the cell and takes a transverse course. It gives off a
 
umber of collaterals which pass towards the bodies of the cells of Purkinje.
 
'hese collaterals terminate by ramifying very freely around the cells of Purkinje
 
s well as around the axons of these cells for a short distance. The minute
 
srminal ramifications form a close basket-work, which encloses the ceil of
 
hirkinje and its axon for a short distance.
 
 
 
The outer cells of the molecular layer are small, and each has several denritic processes and an axon. Each axon springs from the side of the cell,
 
nd, taking a transverse course, it ends in numerous ramifications.
 
 
 
The fibres of the molecular layer are derived from the following sources:
 
1) The dendritic processes, and the recurrent collaterals of the axons of the
 
ells of Purkinje; (2) the dendritic processes and axons of the outer cells; (3) the
 
.endritic processes of the inner or basket cells; (4) the axons of the granule-cells
 
>f the granular layer; (5) the fibres of Bergmann, which represent the processes
 
I glia-cells in the granular layer; (6) the dendrons of the cells of Golgi; and
 
7) some fibres from the white medullary substance of the lamina.
 
 
 
The granular layer consists of (1) nerve- and glia-cells, and (2) fibres.
 
 
 
The nerve-cells are of two kinds—namely, granule-cells and cells of Golgi.
 
 
 
The granule-cells are small and very numerous. They are closely packed
 
ogether, and impart to this layer a granular appearance. Each has several
 
[endrons and one axon. The dendrons soon ramify, and the dendritic processes
 
erminate in minute clusters within the granular layer, which are closely related
 
o the granule-cells. The axon of each granule-cell passes into the molecular
 
ayer, where it ramifies, its branches diverging and being closely related to the
 
[endritic processes of the cells of Purkinje.
 
 
 
The cells of Golgi lie near the cells of Purkinje, and are larger than the granuleells. They are stellate, and each has several dendrons and an axon. The
 
lendrons enter the molecular layer, in which they ramify. The axon ramifies
 
r ery freely in the granular layer. The cells of Golgi may be regarded as associaion cells.
 
 
 
The glia-cells are situated close to the cells of Purkinje, and lie between the
 
mter granule-cells. The superficial processes enter the molecular layer, and
 
onstitute the fibres of Bergmann, which pass as far as the pia-matral covering
 
if the lamina. Their deep processes pass between the granule-cells of the
 
;ranular layer, and some of them enter the white medullary substance.
 
 
 
The fibres of the granular layer are derived from the following sources:
 
1) The axons of the cells of Purkinje; (2) the moss-fibres of Cajal; (3) the denIritic processes of the granule-cells; (4) the ramifications of the axons of the
 
:ells of Golgi; (5) some of the deep processes of the glia-cells; and (6) some fibres
 
rom the white medullary substance.
 
 
 
White Matter.—The white matter of a cerebellai lamina is an
 
>ffshoot of the principal white medullary substance, and composed
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1488
 
 
 
of nerve-fibres. (1) Some of these are the axons of the cells of Purkinje,
 
and these enter the white matter. (2) Others pass through the granular
 
layer into the molecular layer, where they divide into branches which
 
are closely related to the more deeply placed dendritic processes of
 
the cells of Purkinje. (3) A third set terminate in the granular layer,
 
where they divide into branches which present moss-like swellings,
 
furnished with short delicate filaments. These fibres are known as
 
the moss-fibres of Cajal.
 
 
 
Development of the Cerebellum. —The cerebellum is developed from the
 
dorsal laminae of the metencephalon, where this forms the front limb of the
 
pontine flexure. In its growth it extends into the roof-plate.
 
 
 
 
 
4. The Fourth Ventricle.
 
 
 
 
 
The fourth ventricle (ventriculus quartus) is situated behind (1) the
 
upper or open half of the medulla oblongata or bulb, and (2) the
 
pons. It has two walls—ventral and dorsal.
 
 
 
Ventral or Anterior Wall.—This wall is usually referred to as the
 
floor. It is formed by (1) the dorsal surface of the upper or open
 
 
 
half of the bulb, and
 
 
 
 
 
 
 
Fig. 904.— Diagram to show the Composition
 
of Floor and Roof of Fourth Ventricle.
 
 
 
 
 
SMV, IMV, upper and lower medullary vela.
 
 
 
 
 
(2) the dorsal surface of
 
the pons between the converging superior peduncles
 
of the cerebellum. In
 
shape it is rhomboidal,
 
the bulbar and pontine
 
parts being triangular and
 
having their bases applied
 
to each other. The floor
 
is sometimes spoken of as
 
the fossa rhomboidea (see
 
Fig. 892).