_a_, Upper part of lateral fissure (of Sylvius); _b_, cruciate
fissure; _c_, suprasylvian fissure, with its anterior branch (_c′_)
and upper branch (_c″_); _d_, diagonal fissure; _e_, coronal
fissure; _f_, presylvian fissure; _g_, marginal fissure; _h_,
ectomarginal fissure; _i_, entomarginal fissure. (After Ellenberger,
in Leisering’s Atlas.)
]
6. The =marginal fissure= begins behind the cruciate fissure close to
the dorso-medial border and extends in a gentle curve backward almost to
the occipital pole.
7. The =ectomarginal fissure= lies above and nearly parallel to the
posterior part of the suprasylvian fissure.
8. The =entomarginal fissure= lies along the posterior part of the
dorso-medial border.
9. The =calloso-marginal fissure= consists of two separate parts. The
more extensive posterior part is termed the =splenial fissure=. It
extends from the tentorial aspect of the hemisphere in a direction
parallel with the corpus callosum nearly to the middle of the medial
surface; it is continued by the cruciate fissure and is also connected
with the suprasylvian and coronal fissures by branches which pass
obliquely upward and forward. The anterior part, the =genual fissure=,
lies about midway between the anterior part of the corpus callosum and
the dorso-medial border.
10. The =cruciate fissure= is short and shallow. It runs obliquely
upward and forward from the anterior end of the splenial fissure on the
inner surface of the hemisphere.
11. The =sulcus rhinalis= extends in an undulating manner along the
entire lower part of the lateral surface of the hemisphere and forms the
upper limit of the rhinencephalon.
The =olfactory bulbs= are very large and the =tracts= extremely broad
and short. The trigonum olfactorium is so prominent as to be termed the
=tuberculum olfactorium=.
The =cranial nerves= present the following special features:
The =third=, =fourth=, =sixth=, and the =ophthalmic= and =maxillary
divisions= of the fifth nerve, emerge together as in the ox.
The =lacrimal nerve= resembles that of the horse, the =frontal= that of
the ox. The =naso-ciliary nerve= is relatively large and sends numerous
filaments to the ocular muscles. The =maxillary nerve= has a very short
course in the pterygo-palatine fossa. The =infraorbital nerve= is large
in correlation with the development of the snout which receives numerous
branches. The =mandibular nerve= emerges through the foramen lacerum
anterius. The =superficial temporal nerve= is small; according to Moussu
it furnishes the excito-secretory fibers to the upper part of the
parotid gland, while those going to the lower part are derived from the
mylo-hyoid nerve.
[Illustration:
FIG. 535.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, ANTERIOR
VIEW (SCHEMATIC).
_c_, Dorsal common digital nerves; _p_, dorsal proper digital nerves.
]
[Illustration:
FIG. 536.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Volar proper digital nerves.
]
The =inferior buccal nerve= passes downward and forward under cover of
the parotid gland and accompanies the parotid duct, with which it turns
around the lower border of the jaw in front of the masseter.
The =vagus= bears a =jugular ganglion= and a =ganglion nodosum=; the
latter occurs at the point of origin of the superior laryngeal nerve,
and may be as large as a small pea. Proximal to this the vagus is easily
divided into two strands, one of which is the accessory component. The
œsophageal trunks form a posterior œsophageal plexus, as in man, from
which two nerves issue. The inferior nerve is small and ramifies on the
parietal surface of the stomach. The superior trunk is much larger; it
gives branches to the stomach, crosses the lesser curvature of that
organ, and joins the solar plexus.
The =hypoglossal nerve= may present a small dorsal root, on which there
is a minute hypoglossal ganglion (of Froriep).
The =spinal nerves= number on each side eight in the cervical region,
fourteen (commonly) in the thoracic, seven in the lumbar, and four in
the sacral. Some of the special features of the nerves of the limbs are
as follows:
The =brachial plexus= is derived from the same nerves as in the ox, but
the root furnished by the sixth cervical is relatively smaller. The
plexus consists of two parts, the upper of which emerges above the
scalenus, the lower between the two parts of that muscle. The more
important differences in the nerves emanating from the plexus from the
arrangement in the ox occur in the lower part of the limb. The cutaneous
branch of the =radial nerve= divides at the carpus into branches which
concur with the dorsal branch of the ulnar nerve in supplying the
=dorsal digital nerves=, two for each digit. The =volar digital nerves=,
also two for each digit, are formed by the terminal branches of the
=median nerve= and the volar or deep branch of the =ulnar nerve=. The
formation and arrangement of the digital nerves are indicated in the
annexed schematic figures.
[Illustration:
FIG. 537.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal proper digital nerves.
]
[Illustration:
FIG. 538.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Plantar proper digital nerves.
]
The =lumbo-sacral plexus= is derived from the ventral branches of the
last three lumbar and first sacral nerves. The distribution of the
branches of the plexus differs chiefly in the distal part of the limb.
The =superficial peroneal nerve= is large and terminates by forming the
greater part of the =dorsal digital nerves=. The latter, two for each
digit, are also in part formed by the terminal branches of the =deep
peroneal nerve=.
The =tibial nerve= divides at the tarsus into =internal= and =external
plantar nerves=. The latter divide to form the =plantar digital nerves=,
two for each digit. In addition, the external plantar nerve supplies a
branch to the dorsal aspect of the outer (fifth) digit. The arrangement
of the digital nerves is indicated by the annexed schematic figures.
The =sympathetic system= of the pig has received very little attention
from anatomists. The =superior cervical ganglion= is long and fusiform.
It gives off filaments which join the vagus near the ganglion nodosum.
The =cervical trunk= is short and relatively larger than in the ox; it
is inclosed in a common sheath with the vagus in the neck and separates
from that nerve to join the =middle cervical ganglion= at the thoracic
inlet.