Olfactory Area. Uncus, frontal part of hippocampus,
indusium, subcallosal fissures, parolfactory area, and
anterior perforated substance.
Gustatory Area. Probably in region of the olfactory
area in the temporal lobe (uncinate and hippocampal
fissures ?) (not definitely settled).
Language Areas. Emissive (articular) centre for
speech (control of muscles used in speech; larynx,
ANATOMY AND PHYSIOLOGY OF THE BRAIN 367
tongue, jaw muscles). Junction of subfrontal fissure
with the precentral fissure.
Auditory Perceptive Centre (word deafness, also the
lalognostic or word understanding centre). Marginal
fissure and adjacent parts of super- and meditemporal
fissure.
Visual l\<'cc))lic<' Centre (word blindness). Angular
fissure.
/'Jwmm' "Writing" Centre. Medif rental fissure,
in front of motor area for the upper limb (this has not
been definitely proved or accepted).
Language Arrangement Centre. Island of Reil or
insular association area serving to connect the various
receptive sense areas relating to the* understanding
of the written and spoken word with the somesthetic
sensormotor emissary centre related to articulate
speech and writing.
Association Areas. Under this heading are included
the frontal association area concerned, so far as is
known, with the powers of thought in the abstract,
creative, constructive, philosophic, the seat of the will,
memory. The parieto-occipito-temporal area is con-
cerned with the pow r ers of conception of the concrete,
for the comprehension of analogies, comparing, gen-
eralizing, and systematizing things heard, observed,
and felt (Gray).
Sleep. Different theories have been proposed to
account for the causes of sleep, none of which has
been wholly satisfactory.
The most generally accepted theory is based on the
decline in the irritability of the nerve cells of the brain
and associated sense organs, and the development of
fatigue conditions, the result of prolonged activity
(Brubaker). 1
The Peripheral Nerve System. The peripheral
nerve system includes those nerve trunks which
1 See chapter on arteries and veins for blood-supply of brain and
its membranes.
368 THE NERVE SYSTEM
convey impulses to and from the centres in the brain
to the structures of the body. They are divided into
cranial nerves, which do not pass through the spinal
cord, but leave the brain direct from various locations ;
and spinal nerves, which derive their nerve fibers
from the spinal cord and pass out of the spinal canal
by way of the foramen between the vertebra.
The Cranial Nerves. The cranial nerves consist of
twelve pairs, as follows :
I. Olfactory (fila).
II. Optic.
III. Oculomotor.
IV. Trochlear.
V. Trigeminal.
VI. Abducent.
VII. Facial.
Nervus intermedius.
VIII. Acoustic.
1. Cochlearis.
2. Vestibularis.
IX. Glossopharyngeal.
X. Vagus.
XI. Spinal accessory.
1. Accessory to vagus.
2. Spinal part.
XII. Hypoglossal.
These nerves have each a superficial and a deep
origin. The former corresponds to its point of attach-
ment at the surface of the brain; the latter to certain
nuclei or collections of nerve cells in the structure of
the brain. The superficial origin only will be men-
tioned.
THE OLFACTORY NERVES (FIRST). The olfactory
nerves or fila are the special nerves of the sense of
smell. Twenty in number on each side. They are
distributed to the olfactory region in the upper part
ANATOMY AND PHYSIOLOGY OF THE BRAIN 369
of the superior turbinated process of the ethmoid and
corresponding portion of the nasal septum. These
filaments represent the axones of the olfactory cells
FIG. 131
Frontal lobe.
Occipital
lobe.
Base of brain, showing superficial origin of cranial nerves.
and pass through the cribiform plate of the ethmoid
bone to join the under surface of the olfactory bulb,
which rests on the cribriform plate, and is the oval mass
of a grayish color that forms the anterior extremity
24
370 THE NERVE SYSTEM
of a slender process of brain substance, called the
olfactory tract. The olfactory nerves differ in struc-
ture from the other nerves, containing only amyelinic
fibers.
THE OPTIC .NERVES (SECOND) . The fibers of the
optic nerves, the special nerve of the sense of sight,
are situated in the retina; they start as the central
processes of the ganglion cells which converge and
pierce the choroid and sclera as a cylindric cord. The
point of emergence is situated a little internal to the
posterior pole of the globe. Passing through the orbital
fat, in an inward and backward direction, it passes
through the optic foramen to end in the optic chiasm
or commissure. The optic chiasm is somewhat quadri-
lateral in shape, rests on the olivary eminence and the
diaphragma sellse, being bounded above by the lamina
terminalis; behind, by the tuber cinereum, on either
side by the anterior perforated substance. Within
the chiasm the fibers cross as follows: Those from
the nasal side of the left and right halves of the retina
cross in the centre, to the opposite optic tract; those
from the temporal side of the right and left eyes pass
backward without crossing, to end in the optic tract
of the same side.
The optic tract passes back to areas of the brain
where the nerve impulses are conveyed to the cuneus
(the area for the sense of sight in the cortex) by means
of another pathway, the optic radiation. By connections
with other nerve centres in the brain the optic tract
communicates w r ith the origin of the nerves which
influence the muscles that control the movements of
the eye-ball.
THE OCULOMOTOR (THIRD). The oculomotor arises
superficially from the crus anterior to the pons, its
deep origin being a gray nucleus in the floor of the
aqueduct of Sylvius. It runs to the outer side of the
posterior clinoid process of the sphenoid bone, enters
ANATOMY AND PHYSIOLOGY OF THE BRAIN 371
the cavernous sinus, runs above the other nerves in
its outer wall, and divides into two branches, which
enter the orbit between the two heads of the external
rectus. It is joined in the sinus by sympathetic fila-
ments. The superior branch crosses the optic nerve
to supply the superior rectus and levator palpebrse
muscles. The inferior divides into three parts one
for the inferior oblique, one to the inner, and one to
the lower recti muscles. The first supplies the motor
root of the lenticular ganglion of the sympathetic
system.
THE TROCHLEAR (FOURTH). The trochlear nerve
has an apparent origin from the upper side of the
valve of Vieussens, and a deep from the floor of the
aqueduct of Sylvius. The two nerves communicate
by a transverse band on the valve of Vieussens. The
nerve pierces the dura after crossing over the cms,
enters the cavernous sinus, in w T hose outer wall it lies
between the ophthalmic and third nerves, then crosses
the latter to enter the orbit through the sphenoidal
fissure above the external rectus, and enters the
superior oblique muscle.
THE FIFTH NERVE (TRIFACIAL). The fifth or
trifacial is the largest of all the cranial nerves, and
arises by two roots, a motor and a sensor. The former
is small, and the latter has the Gasserian ganglion
upon it. Both arise from the side of the pons super-
ficially, the smaller root above the larger, some trans-
verse fibers of the pons separating the two. This
nerve conveys both motion and sensation. At the
apex of the petrous portion of the temporal the large
root forms the Gasserian ganglion; the smaller does
not join in the ganglion, but runs below it to join,
just below the foramen ovale, the lowest trunk pro-
ceeding from the ganglion.
The Gasserian ganglion lies in a hollow near the apex
of the petrous portion of the temporal bone, the large
372
THE NERVE SYSTEM
superficial petrosal nerve, and the motor root lying
below it. It receives branches from the carotid
FIG. 132
Sensory root
Motor root.
Auriculo-temporal
nerpe
Distribution of the second and third divisions of the fifth nerve and
submaxillary ganglion. (Gray.)
plexus. Small twigs pass to the dura mater. This
ganglion sends off three large branches, vi/., the
ophthalmic, superior maxillary, and inferior maxillary.
ANATOMY AND PHYSIOLOGY OF THE BRAIN 373
The first two confer sensation, the third, motion
and sensation.
The ophthalmic nerve, or first division of the fifth
nerve, is sensor and the smallest branch of the ganglion.
It is flattened, about 1 inch long. It receives filaments
from the cavernous plexus, and gives off filaments to
the third and sixth, and sometimes to the fourth nerve,
FIG. 133
Internal carotid artery
and carotid plexus.
Ophthalmic . .
(ciliary) gangli -n. S- :
?il ^
SI
Nerves of the orbit and ophthalmic ganglion. Side view. (Gray )
and a recurrent branch running in the tentorium cere-
belli with the fourth. Finally, it divides into the
frontal, lacrymal, and nasal nerves, which pass through
the sphenoidal fissure into the orbit.
The second division of the fifth nerve (superior
maxillary) is sensor, and enters the foramen rotund urn,
374 THE NERVE SYSTEM
crosses the sphenomaxillary fossa, and, as the infra-
orbital, traverses the canal, emerges from the foramen
to end on the face in .the palpebral, nasal, and labial
branches the first set, to lower lid; the second, to
side of nose; and the third, to upper lip.
The orbital or temporomalar branch enters the orbit
by the sphenomaxillary fissure, and divides into two
branches, which pierce the malar bone.
The alveolar or superior dental nerves are three:
The posterior, middle, and anterior, which supply the
upper row of teeth.
The inferior maxillary nerve (third division of the
fifth) is the largest branch, and arises by two roots
a large sensor root from the Gasserian ganglion and
the motor root of the fifth. This nerve divides into
two trunks, anterior and posterior. The anterior gives
off the masseteric, the buccal, the deep temporal, and
the two pterygoid nerves.
The posterior trunk of the inferior maxillary is
mostly sensory. It divides into the auriculotemporal,
gustatory, and inferior dental; the last supplies the
low^er row of teeth.
The gustatory or lingual nerve lies at first beneath
the external pterygoid, internal to the dental nerve.
Here a branch from the dental may cross the internal
maxillary to join it. The chorda tympani also
joins it.
The nerve now runs along the inner side of the
ramus of the jaw, and crosses the upper constrictor to
the side of the tongue above the deep part of the
submaxillary gland; lastly, it runs below Wharton's
duct, and superficially along the side of the tongue to
its apex. It communicates with the facial through
the chorda tympani, the submaxillary ganglion,
inferior dental, and hypoglossal. It supplies the
mucous membrane of the mouth and tongue (anterior
two-thirds), the gums, sublingual gland, and the
ANATOMY AND PHYSIOLOGY OF' THE BRAIN 375
filiform and fungiform papillae in the mucous mem-
brane on the back of the tongue.
THE SIXTH NERVE. The sixth or abducens has
an apparent origin in the groove between the pons
and medulla. It runs to the lower and outer part
of the dorsum sellse, and traverses the floor of the
cavernous sinus external to the carotid artery, and,
receiving branches from the cavernous and carotid
plexuses, enters the orbit by the sphenoidal fissure
dirision oj oculo-motoi\
Nasal.
Inferior division of oculo-motor.
'Abducent.
'Ophthalmic rein.
Relations of structures passing through the sphenoidal fissure. (Gray.)
between the two heads of the external rectus; it
receives a branch from the ophthalmic nerve, and
supplies the above-named muscles.
THE SEVENTH NERVE. The seventh or facial
has a superficial origin from the depression between
the olivary and restiform bodies of the medulla oblon-
gata. Between it and the eighth is the pars inter-
media, which joins the facial in the auditory canal.
The nerve runs outward to the internal meatus,
where it runs in a groove on the auditory nerve,
enters the aqueductus Fallopii, and emerges at the
376
THE NERVE SYSTEM
FIG. 135
The nerves of the scalp, face, and side of the neck. (Gray.)
ANATOMY AND PHYSIOLOGY OF THE BRAIN 377
stylomastoid foramen. It presents within the aque-
duct, near the hiatus Fallopii, a reddish enlargement,
the geniculate ganglion. Outside the cranium it
runs forward in the parotid gland, and divides behind
the ramus into the cervicofacial and temporofacial
divisions. In the parotid and vicinity the radiating
branches form the pes anserinus.
The facial nerve supplies all the muscles of expres-
sion of the face.
THE AUDITORY NERVE. The eighth or auditory
is the special nerve of the sense of hearing. Super-
ficially it appears at the lower border of the pons,
external to the facial. It has two roots one from the
inner side of and one from the front of the restiform
body. It runs to the internal auditory meatus with
the facial nerve, the two being separated by the pars
intermedia and the auditory artery. The nerve in
the meatus divides into a cochlear and a vestibular
branch, whose distributions within the ear are described
under the special sense of hearing.
THE NINTH NERVE. The ninth or glossopharyngeal
arises superficially by several filaments from the
groove between the olivary and restiform bodies at
the upper part of the medulla; deeply through the
lateral tract to a gray nucleus in the floor of the
fourth ventricle.
The nerve runs through the middle part of the jugular
foramen with the vagus and spinal accessory, in a
separate sheath, and here presents two successive
ganglionic enlargements, the jugular and the petrous
ganglia. Outside the cranium it passes between the
jugular vein and the internal carotid artery, descending
in front of the latter, and beneath the styloid process
and its muscles, to the lower border of the stylo-
pharyngeus, and supplies the mucous membrane of
the tongue. It then crosses this muscle and divides
into branches beneath the hyoglossus. In the jugular
378 THE NERVE SYSTEM
foramen it grooves the lower border of the petrous
portion of the temporal bone.
THE PNEUMOGASTRIC NERVE. The tenth, vagus,
or pneumogastric is both motor and sensor. Its
apparent origin is by twelve to fifteen filaments
below, and in the line of the origin of the ninth; its
deep origin is from a nucleus in the lower part of the
fourth ventricle. It passes through the jugular foramen
in the same sheath with the spinal accessory, a par-
tition separating them from the ninth, and develops
the ganglion of the root of the vagus. Emerging from
the foramen, it forms the ganglion of the trunk of the
vagus.
The ganglion of the root (ganglion jugulare) is gray
in color and spherical, its diameter about two lines.
It has branches of communication with the accessory
part of the spinal accessory, with the petrous ganglion
of the ninth, with the facial, and 'with the superior
cervical ganglion of the sympathetic.
The ganglion of the trunk (ganglion cervicale) is
larger, of a reddish color, and cylindrical form. Its
surface is crossed by the accessory portion of the
eleventh, and it communicates with the hypoglossal,
the upper two cervical, and the sympathetic nerves.
The vagus then descends between the internal
carotid artery and the jugular vein to the thyroid
cartilage, then between the vein and the common
carotid to the root of the neck; where it enters the
thorax and gives off branches to the heart (cardiac
plexuses), lungs (pulmonary plexuses), and esophagus;
it then passes through the esophageal opening in the
diaphragm to enter the abdominal cavity where it
gives off branches to the solar plexus, the stomach,
liver, spleen, kidneys, suprarenal glands, and pan-
creas.
THE ELEVENTH PAIR. The eleventh, or spinal
accessory, consists of si spinal portion and an accessory
ANATOMY AND PHYSIOLOGY OF THE BRAIN 379
part to the vagus. The latter part arises as five or
six filaments from the lateral tract of the medulla,
below the origin of the vagus.
The spinal portion arises from the lateral column
of the cord as low as the sixth cervical nerve, the
fibers being connected with the anterior horn of gray
matter. This part then ascends, between the posterior
nerve roots and the ligamentum denticulatum, through
the foramen magnum, then out again by the jugular
foramen, lying in the sheath of the vagus, and here
communicates with the accessory portion. After
its exit from the skull it crosses the internal jugular
vein and pierces the sternomastoid to end in the
trapezius muscle.
THE HYPOGLOSSAL. The twelfth, or hypoglossal,
nerve arises by ten to fifteen filaments from the groove
between the pyramid and olivary body in the medulla.
The deep origin is from a nucleus in the floor of the
fourth ventricle. The filaments form two bundles
which pierce the dura separately and unite in the
anterior condylar foramen. The nerve descends behind
the internal carotid artery and internal jugular vein,
closely bound to the vagus. 1
The Spinal Nerves. The spinal nerves consist, on each
side, of eight cervical, twelve thoracic, five lumbar,
five sacral, and one coccygeal, in all thirty-one pairs,
which arise from the cord by two roots, anterior and
posterior. The latter are the larger, and are supplied
with ganglia. The suboccipital or first cervical nerve
has no ganglion. The two roots unite just beyond
the ganglion, and the resulting trunk divides into two
divisions, anterior and posterior, each containing
fibers from both roots, sensor and motor. The posterior
division divides into an external and an internal branch.
The anterior divisions in the dorsal region remain
separate, but elsewhere they unite into plexuses.
1 See Fig. 131 for origin of spinal nerves.
380 THE NERVE SYSTEM
They are larger than the posterior. Each division is
connected with the sympathetic ganglia along the
vertebral column, by means of nerve trunks called
rami communicantes. (See Sympathetic System, p.
385.)
THE CERVICAL PLEXUS. The cervical plexus is
formed by the anterior divisions of the upper four
cervical nerves, which emerge between the scalenus
medius and rectus anticus major. It lies upon the
scalenus medius and levator anguli scapulae, beneath
the sternomastoid. Each nerve except the first
divides into a branch for the nerve above and one for
the nerve below. The anterior division of the first
(suboccipital) nerve grooves the atlas beneath the
vertebral artery, and joins the second, supplying the
rectus lateralis and recti antici muscles. It commu-
nicates with the sympathetic vagus, and hypoglossal
nerves.
Its branches are superficial and deep.
The superficial are divided into ascending and
descending.
Ascending Branches. (a) The superficialis colli,
(b) auricularis magnus (great auricular), (c) occipital
minor.
Descending Phrenic, from the third, fourth, and
fifth, descends on the scalenus anticus, then between
the subclavian artery and vein, and crosses the internal
mammary artery. It then crosses in front of the root
of the lung and runs between the pericardium and
mediastinal pleura to the diaphragm.
THE BRACHIAL PLEXUS. The brachial plexus is
formed by the anterior divisions of the lower four
cervical and first thoracic, as follows: The fifth arid
sixth form an upper; the seventh, a middle; and the
eighth cervical with first dorsal a lower trunk. Each
of these trunks then separates into an anterior and a
posterior branch.
ANATOMY AND PHYSIOLOGY OF THE BRAIN 381
The anterior branches of the upper and middle
trunks form the outer cord of the plexus; the anterior
branch of the lower, the inner cord; of the posterior
cord it is variously stated that the posterior branches of
all three trunks form it, or that the posterior branches
of the upper and middle trunks form it, while the
FIG. 136
V Cervical
Anterior division of Upper Trunk
External Anterior Thoracic
Posterior division of Upper Trunk
Middle and Lo
Sub-scapular
Circumflex
Anterior division of Lower Trunk
Posterior division of Lower Trunk
Internal Anterior Thoracic
Lesser Internal Cutai,
Internal Cutu
Musculu-cutaneuus
Ulnar/
Musculo-spiral'
Plan of the brachial plexus. (Gray.)
posterior branch of the lower trunk joins the musculo-
spiral nerve. It is altogether a matter of dissection.
The plexus is at first between the anterior and middle
scaleni, then above and external to the subclavian
artery. It passes behind the clavicle and subclavius,
lying on the subscapularis and serratus magnus muscles.
The cords lie external to the first part of the axillary
382 THE NERVE SYSTEM
artery, but on three sides of the second part of that
vessel.
The branches of the brachial plexus supply the
muscles of arm, forearm, fingers, and the muscles
of the chest.
THE LUMBAR PLEXUS. The lumbar plexus is formed
in the substance of the psoas muscle, in the following
manner: Each of the first four lumbar nerves divides
into an upper and a lower branch. Just before dividing
the first receives the twelfth thoracic nerve, and the
third and fourth send each a branch to the nerve below.
The upper branch of the first subdivides into the
iliohypogastric and ilioinguinal nerves. The lower
branch of the first passes downward and subdivides
into two branches, one of which unites with the
upper branch of the second to form the genitocrural
nerve. The other unites with the lower branch of the
second to form a cord. This cord passes downward,
and gives off the external cutaneous nerve and a branch
to the obturator, after which it unites with the upper
branches of the third and fourth to form the anterior
crural nerve. The lower branches of the third and
fourth unite to form the obturator nerve.
The branches derived from the above plexus inner-
vate the skin and muscles over the anterior and
internal aspect of the thigh, leg, instep, and external
genital organs.
THE SACRAL PLEXUS. The sacral plexus is formed
by the anterior divisions of the first, second, third,
and part of the fourth sacral nerves, together with the
lumbosacral cord.
The lumbosacral cord, with the first, second, and
part of the third sacral nerve, is continued into the
upper great branch of the plexus, and the remainder of
the plexus forms the lower or smaller branch.
The branches from this plexus supply the muscles
and skin over the buttocks, back of thigh and leg,
and the sole of the foot.
THE SYMPATHETIC NERVE SYSTEM 383
THE SYMPATHETIC NERVE SYSTEM
The sympathetic system consists of numbers of
ganglia connected with one another by extension of
their nerve trunks. It is not an independent system
for the conveyance of nerve impulses, but is in rela-
tion with the cerebrospinal system of nerves through
communicating branches.
The ganglia are classified - as central ganglia which
are arranged on either side of the spinal column, and
are connected to each other by nerve trunks, forming
the gangliated cord. The central ganglia extend from
the base of the skull to the coccyx, and communicate
with the spinal nerves by means of nerves called rami
communic antes.
The ganglia of the cord are classified for purpose
of study into the following groups:
Cervical portion 3 pairs of ganglia.
Thoracic portion . . . . 10 to 12 pairs of ganglia.
Lumbar portion 4 pairs of ganglia.
Sacral portion 4 or 5 pairs of ganglia.
The ganglia of the sympathetic system are further
arranged into minute plexuses called the three great
gangliated plexuses. They are situated in the thoracic
and abdominal cavities and receive interconnecting
nerve trunks which form the following plexuses: (1)
The cardiac, which receives nerve trunks from the
upper three cervical ganglia, and gives off peripheral
branches to the heart, lungs; (2) the solar or celiac
plexus, which receives nerve trunks (splanchnic nerves)
from the thoracic portion and gives off terminal
branches which form underlying plexuses and inner-
vate the muscles of the intestinal wall, and other
organs of the abdominal cavity, bloodvessels, and
secreting cells of glands; (3) the hypogastric plexus,
which receives branches from the lumbar and sacral
384
THE NERVE SYSTEM
Superior cervical ganglion
Middle cervical ganglion
/
Injertor cervical ganglion
Pharyngeal branches
Cardiac branches.
Deep cardiac plexus.
Superficial cardiac plexus
Solar plexus.
Aortic plexus
Hypngastric plexus
Sacral ganglia.
Ganglion impar
The sympathetic ucrve system.
THE SYMPATHETIC NERVE SYSTEM 385