_a_, Transverse fissure; _b_, lateral fissure (of Sylvius); _c_,
coronal fissure; _d_, diagonal fissure; _e_, entomarginal fissure;
_f_, marginal fissure; _g_, ectomarginal fissure; _h_, suprasylvian
fissure. (After Ellenberger, in Leisering’s Atlas.)
]
1. The =lateral fissure= (of Sylvius) is very deep. Its middle branch
extends almost vertically upward on the middle of the lateral surface
of the hemisphere, and is separated by a gyrus of variable width from
the suprasylvian fissure. The anterior branch runs forward about
parallel with the sulcus rhinalis anterior, from which it is separated
by the short gyri of the insula. The latter are covered to a small
extent only by the overhanging gyri (operculum). The posterior branch
may run back a distance of only about 1.5 cm. and end in T-shaped
manner, or it may join the sulcus rhinalis posterior.
2. The =suprasylvian fissure= is deep and very distinct. It extends in
an undulating manner from the lateral surface of the occipital pole to
the outer side of the sagittal pole. Here it may be interrupted or may
be continued by the =coronal fissure=, which descends to the frontal
pole and divides into two short branches.
3. The =diagonal fissure= (S. diagonalis) begins in front of the stem
of the lateral fissure and runs upward and forward. Its form is very
variable.
4. The =transverse fissure= cuts obliquely into the dorsal border in
front of the sagittal pole. It is short and deep and commonly
communicates with the suprasylvian and coronal fissures.
5. The =marginal fissure= is distinct. It extends from the sagittal
pole to the occipital pole. It is flexuous and deviates outward
somewhat in its posterior two-thirds.
6. The =entomarginal fissure= lies medial and parallel to the
posterior part of the preceding.
7. The =ectomarginal fissure= is lateral and parallel to the marginal
fissure. It does not extend so far in either direction as the latter
and is often more or less broken up by annectent gyri.
8. The =sulcus rhinalis= is more open than in the horse, since it is
not overlapped by the gyri above it.
9. The =calloso-marginal= fissure is flexuous and not so regular as in
the horse. It is often interrupted at or near the level of the genu of
the corpus callosum, in which case the =genual fissure= continues it
downward.
10. The =crucial fissure= is faint and is confined to the medial
surface. It lies about one centimeter in front of the transverse
fissure and commonly joins the calloso-marginal fissure below.
11. Short and variable fissures occur in front of and behind the
middle branch of the lateral fissure (F. ectosylvia anterior,
posterior).
The =olfactory bulb= is much smaller than in the horse. The external
olfactory tract is large, the inner one small and not distinct.
The =cranial nerves= have in general the same superficial origin as in
the horse. The more important differences in other respects are as
follows:
The =oculomotor nerve= is larger than in the horse. It emerges with the
fourth, sixth, ophthalmic, and maxillary nerves through the large
foramen, which is equivalent to the foramen lacerum orbitale and foramen
rotundum of the horse.
The internal branch of the =lacrimal nerve= supplies twigs to the mucous
membrane of the frontal sinus; the large outer branch runs backward and
supplies the matrix of the horn. The =frontal nerve= emerges from the
orbit below the supraorbital process. The =naso-ciliary nerve= is large
and sends filaments to the ocular muscles. The =ciliary ganglion= is
somewhat larger than in the horse and is connected with the lower
division of the oculomotor nerve by several short filaments. In
consequence of the absence of the canine and upper incisor teeth the
corresponding branch of the infraorbital nerve is naturally wanting. The
=mandibular nerve= emerges through the foramen ovale. The =superficial
temporal nerve= gives off a large branch which joins the superior buccal
division of the facial on the masseter, about half-way between the
zygomatic arch and the angle of the jaw. The =otic ganglion= is larger
than in the horse. According to Moussu the buccinator nerve furnishes
excito-secretory twigs to the parotid and inferior buccal glands.
The =facial nerve= divides into its two terminal branches before
reaching the border of the jaw. The =superior buccal nerve= is the
larger of the two; it crosses the masseter much lower than in the horse.
The relatively small =inferior buccal nerve= runs beneath the parotid or
in the gland substance parallel with the border of the lower jaw,
crosses under the insertion of the sterno-cephalicus, and runs forward
along the depressor labii inferioris. At the point where it crosses the
facial vein and parotid duct it gives off an anastomotic branch to the
superior nerve. The =auriculo-palpebral nerve= is large.
The =vagus= bears—in addition to the relatively large =jugular
ganglion=—a =ganglion nodosum= at the point of origin of the superior
laryngeal nerve. The trunk is large. The =pharyngeal branch= is large
and anastomoses with the superior and external laryngeal nerves. The
latter commonly arises directly from the trunk. The =superior œsophageal
trunk= communicates with the splanchnic nerve, contributes twigs to the
hepatic plexus, and ramifies chiefly on the right surface of the rumen
and the adjacent surface of the abomasum. The =inferior œsophageal
trunk= supplies branches to the hepatic plexus and to all the divisions
of the stomach.
The =spinal accessory nerve= presents two special features. The part
which joins the jugular ganglion bears a small ganglion. The ventral
branch supplies both parts of the sterno-cephalicus.
The =hypoglossal nerve= is large. It is connected with the ventral
division of the first cervical nerve by a branch of considerable size,
and detaches a long branch which runs backward along the carotid artery.
The =spinal nerves= resemble those of the horse in origin and general
arrangement. The thoracic nerves number thirteen pairs. The more
important differences in the limb-plexuses and their branches are as
follows:
The =brachial plexus= is formed by the ventral branches of the last
three cervical and first thoracic nerves; the second thoracic nerve
furnishes no root, but the ventral branch of the sixth cervical goes
almost entirely to the plexus after giving off the nerve to the
rhomboideus and the cervical part of the serratus magnus.
The differences in the nerves above the elbow are not of sufficient
moment to receive notice in this brief account, but below this point
there are naturally important special features correlated chiefly with
the arrangement of the digits.
The =radial nerve= is continued below the elbow by a large =cutaneous
branch= (N. cutaneus antibrachii dorsalis) which emerges at the lower
border of the external head of the triceps and descends on the dorsal
aspect of the limb. It communicates above the carpus with the cutaneous
branch of the median nerve and terminates in three =dorsal digital
nerves=; two of these descend along the axial or interdigital side of
the dorsal surface of the chief digits, and the third along the inner
(abaxial) side of the inner chief digit.
[Illustration:
FIG. 530.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF OX, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal digital nerves.
]
[Illustration:
FIG. 531.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF OX, POSTERIOR
VIEW (SCHEMATIC).
_p_, Volar digital nerves.
]
The =ulnar nerve= divides at a variable distance down the forearm into
two branches. The =dorsal= or =superficial branch= emerges between the
tendons of the external and middle flexors of the carpus, and is
continued as the =external dorsal digital nerve= on the outer chief
digit. The =volar= or =deep branch= descends along the superficial
digital flexor, gives a branch to the suspensory ligament below the
carpus, and unites with the external branch of the median nerve to form
the =external volar digital nerve=.
The =median nerve= is much larger than the ulnar. It passes beneath the
pronator teres, descends the forearm as in the horse, and divides in the
distal part of the metacarpus into two branches. The =internal branch=
gives twigs to the inner small digit and is continued on the inner side
of the volar surface of the inner chief digit as the =internal volar
digital nerve= (N. digitalis medialis digiti III); it also concurs with
the outer branch in forming the two digital nerves which descend along
the interdigital aspect of the chief digits. The =external branch= is
larger. It bifurcates, and one division unites with the twig from the
internal branch to form a common digital trunk. From the latter two
digital nerves proceed as mentioned above; these are the =external= and
=internal volar digital nerves= of the internal and external chief
digits respectively (N. digitalis volaris lateralis digiti III, medialis
digiti IV). The other division unites with the volar branch of the ulnar
nerve to form the =external volar digital nerve= of the external chief
digit (N. digitalis lateralis digiti IV).
[Illustration:
FIG. 532.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF OX, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal digital nerves.
]
[Illustration:
FIG. 533.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF OX, POSTERIOR
VIEW (SCHEMATIC).
_p_, Plantar digital nerves.
]
The =lumbo-sacral plexus= and its branches to the pelvis and thigh
present no very striking special features.
The =superficial peroneal nerve= is much larger than in the horse. After
crossing beneath the peroneus longus it passes down on the front of the
tarsus and metatarsus and divides into three branches. The internal and
external branches descend as the =internal= and =external dorsal digital
nerves= on the chief digits. The larger middle branch joins a branch of
the deep peroneal nerve in the interdigital space, and from this union
proceed the =dorsal digital nerves= which descend on the opposed
surfaces of the chief digits.
The =deep peroneal nerve= descends in the leg as in the horse and
continues down the anterior groove of the metatarsus with the dorsal
metatarsal artery. Its terminal branches concur with branches from the
superficial peroneal nerve in the formation of the two axial =dorsal
digital nerves= (N. dig. dors. lat. dig. III et dig. dors. med. dig. IV
pedis), and with a branch of the internal plantar nerve in the formation
of corresponding plantar digital nerves.
The =tibial nerve= divides at the back of the hock into internal and
external plantar nerves. The =internal plantar nerve= descends between
the superficial flexor tendon and the suspensory ligament and divides
into two branches; the inner branch descends as the =internal plantar
digital nerve= (N. dig. plant. med. dig. III) along the inner side of
the flexor tendons of the inner chief digit; the outer branch turns
around the flexor tendons to reach the interdigital space, where it
concurs with a branch of the deep peroneal nerve in the formation of two
=axial plantar digital nerves= (N. dig. plant. lat. dig. III et dig.
plant. med. dig. IV) which descend on the opposed surfaces of the chief
digits. The =external plantar nerve= descends along the outer border of
the flexor tendons, gives a branch to the suspensory ligament and to the
external small digit, and continues along the outer face of the external
digit as the =external plantar digital nerve= (N. dig. plant. lat. dig.
IV).
The =sympathetic system= closely resembles that of the horse in its
general arrangement, and only a few differential features will receive
attention. The =superior cervical ganglion= is closer to the cranial
base and is thicker than in the horse; its branches to the carotid and
cavernous plexuses are large, and no connection is formed with the
spinal accessory nerve. The =cervical trunk= is smaller than in the
horse, and arises by two or three bundles from the superior cervical
ganglion behind its middle. The =inferior cervical ganglion= is
distinctly separable from the first thoracic; the latter is large. There
are thirteen pairs of =thoracic ganglia=. The =cœliaco-mesenteric
ganglia= are plexiform, not compact. There are five pairs of =sacral
ganglia=, and the right and left trunks are connected here by transverse
anastomoses.