Part 85

The =posterior mesenteric plexus= (P. mesentericus caudalis) accompanies the artery of like name in its distribution.

The secondary plexuses which accompany the branches of the mesenteric arteries give off branches which form two fine peripheral plexuses in the wall of the intestine. One of these, the =myenteric plexus= (P. myentericus) or plexus of Auerbach, lies between the layers of the muscular coat, and is provided with microscopic ganglia. The other is in the submucous tissue, and is therefore termed the =submucous plexus= (P. submucosus) or plexus of Meissner.

The following paired plexuses are derived mainly from branches of the cœliac and aortic plexuses:

1. The =renal plexuses= (P. renales) proceed largely from the cœliaco-mesenteric ganglia, but receive fibers also from the small splanchnic nerves. They enlace the renal arteries and supply the kidneys. Minute renal ganglia occur on the course of the nerves along the renal vessels.

2. The =adrenal plexuses= (P. suprarenales) are formed by a relatively very large number of fine fibers derived in great part directly from the cœliaco-mesenteric ganglia. Numerous minute ganglia occur in their meshes.

3 _a_. The =spermatic plexuses= (P. spermatid) proceed largely from the aortic and renal plexuses. Each accompanies the corresponding (internal) spermatic artery to the testicle.

3 _b_. The =utero-ovarian plexuses= (P. ovarici) are the homologues in the female of the preceding. They accompany the utero-ovarian arteries to the ovary and the cornua of the uterus.

The =hypogastric= or =pelvic plexus= (P. hypogastricus) is the pelvic continuation of the aortic and posterior mesenteric plexuses. The chief nerves which form it enter the pelvic cavity ventral to the large vessels, anastomose with each other and with branches from the third and fourth sacral nerves, and ramify on the pelvic viscera. The peripheral plexuses derived therefrom are named according to the organs which they supply; the chief of these are the =hæmorrhoidal=, =vesical=, =uterovaginal=, =prostatic=, =cavernous= (of the penis or clitoris).

THE NERVOUS SYSTEM OF THE OX[214]

The =spinal cord= resembles that of the horse in conformation and structure. In cattle of medium size its length is about 165 to 170 cm. (ca. 65 to 67 inches) and its weight about 240 to 250 grains (ca. 8 ounces).

In a cow 140 cm. in height Dexler found the weight of the cord (including the intradural nerve-roots) to be 260 g. and the length 162 cm. The lengths of the regions were: cervical 41 cm., thoracic 72 cm., lumbar 32 cm., sacral 7 cm.

The =brain= has an average weight of about 500 grams (ca. 16 to 17 ounces). Its differences in general form are correlated with those noted in the consideration of the cranial cavity.

The =medulla= is short, wide, and thick. Its ventral face is strongly convex. The pyramids are narrow, short, and close together in front. Near the decussation there is a well defined oval prominence on either side which indicates the position of the posterior olive. The corpus trapezoideum is large; it has no central part between the pyramids. The external arcuate fibers are distinct. The restiform bodies are short and thick and diverge more strongly than in the horse. The floor of the fourth ventricle is only about two-thirds as long as in the horse. The area acustica is a well-marked oval prominence lateral to the middle part of the limiting sulcus. The tuberculum acusticum at the origin of the auditory nerve is very large. The anterior fovea is distinct. The posterior recess of the fourth ventricle communicates through the foramen of Magendie (Apertura mediana) with the subarachnoid space.

The =pons= is smaller, both transversely and longitudinally, than that of the horse. It is strongly convex and has a distinct central depression.

The =cerebellum= is smaller and more angular in form than in the horse. The vermis is large and has a distinct depression on its anterior face for the posterior corpora quadrigemina. The hemispheres are relatively small and are not clearly divided into tabulations. The anterior peduncles are very short.

The =cerebral peduncles= are short. A small eminence in the locus perforatus posticus is caused by the presence of the interpeduncular ganglion. The =internal geniculate body= is prominent. The =pineal body= is long and fusiform, and is often pigmented in spots. The third ventricle forms two considerable recesses in relation to the pineal body: one (R. pinealis) extends up into the body; the other (R. suprapinealis) is a long tubular prolongation in front of it.

The =optic tracts= cross the cerebral peduncles almost at a right angle.

The =pituitary body= is situated in a deep fossa and is surrounded by a plexus of vessels.

The =cerebral hemispheres= are shorter, higher, and relatively wider than in the horse. The frontal poles are small, the occipital large. Viewed from the side, the dorsal surface is strongly convex. The highest point of the dorso-medial border is a little in front of its middle and forms a marked prominence termed the =sagittal= or =marginal pole= (Polus sagittalis s. prominentia marginalis dorsalis). Anterior to this the border drops abruptly, being cut into by the deep transverse fissure. The arachnoid on the basal and anterior parts of the hemispheres is usually pigmented. The =corpus callosum= extends through a little more than a third of the length of the hemisphere. The pattern of the =fissures= and =gyri= of the pallium is somewhat simpler than in the horse.

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.

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).

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.

THE NERVOUS SYSTEM OF THE PIG

The =spinal cord= weighs about 42 grams (Ellenberger-Baum). It is almost circular in cross-section, except at the enlargements, where it is somewhat flattened dorso-ventrally. The conus medullaris extends to the anterior part of the third sacral segment. The epidural space is occupied by a large quantity of fat.

The =brain= in adults of medium size weighs about 125 grams (ca. 4 to 4½ ounces). When viewed from above, it is seen to have an elongated oval form. The occipital poles overlie the cerebellum to a small extent only; the frontal poles are rounded and relatively large, but do not conceal the ends of the olfactory bulbs. The =medulla= is relatively broad. The cuneate tubercle is very large and is limited externally by a groove. The corpus trapezoideum is very wide laterally. The =pons= is less prominent than in the ox. The =cerebellum= is very wide and short. Its anterior face is flattened and presents a depression for the corpora quadrigemina. The vermis is large. The hemispheres consist of an inner large and an outer small part. The =cerebral peduncles= are very short. The posterior corpora quadrigemina are wide apart, rounded, and relatively large. The internal geniculate body is prominent. The =cerebral hemispheres= are somewhat bean-shaped in lateral profile, the convex border being dorsal. The arrangement of the gyri and sulci is simpler than in the horse or ox. The principal fissures are as follows:

1. The =lateral fissure= (of Sylvius) begins at the sulcus rhinalis and runs upward and somewhat backward on the depressed part of the lateral surface of the hemisphere; it appears unbranched on superficial examination, but when the gyrus which almost completely conceals the insula is raised, an anterior branch is exposed which forms the dorsal boundary of the insula.

2. The =suprasylvian fissure= pursues a curved course approximately parallel with the dorso-medial border of the hemisphere. Its posterior end is separated by a short interval from the sulcus rhinalis posterior. From its highest point a branch proceeds obliquely upward and forward, crosses the dorso-medial border, and joins the splenial fissure.

3. The =diagonal fissure= crosses the anterior part of the lateral surface. It is directed obliquely downward and backward.

4. The =coronal fissure= is constant and deep. It is directed upward and inward over the frontal pole, continues backward near the dorso-medial border, and usually ends by passing obliquely over the border to the inner surface of the hemisphere.

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.

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.