Part 217

5. The =presylvian fissure= begins—apparently as a branch of the sulcus rhinalis anterior—about 2 cm. in front of the lateral fissure, and curves over the lateral aspect of the frontal pole.

FIG. 534.—CEREBRAL HEMISPHERES OF PIG, DORSAL VIEW.

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.

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. ]

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.

FIG. 537.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, ANTERIOR VIEW (SCHEMATIC).

p, Dorsal proper digital nerves. ]

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.