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.

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.

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.

THE NERVOUS SYSTEM OF THE DOG

The spinal cord is almost circular in cross-section except at the well-marked cervical and lumbar enlargements, where it is compressed dorso-ventrally. The conus medullaris lies over the junction of the sixth and seventh lumbar vertebræ. The length of the cord of a rather large dog was found to be about 38 cm.; of this, the cervical part was 11 cm., the thoracic 17.4 cm., the lumbar about 7 cm., and the sacro-coccygeal about 2.6 cm. (Flatau-Jacobson).

The brain weighs about 60 to 70 g. in dogs of medium size, but there is, of course, a wide range of weight in the different breeds. Thus in small terriers the weight is 30 g. or even less, while in very large dogs it may exceed 150 g. It corresponds much more closely with the cranium in size and general form than in the animals previously described; this is specially true of the small breeds, in which the bony crests and frontal sinuses are little developed.

The medulla is broad and thick. Its ventral surface is strongly convex from side to side. The pyramids are large and prominent and are limited by distinct median and lateral grooves. The olivary eminence is a well defined oval elevation situated between the pyramid and the superficial origin of the hypoglossal nerve. The external arcuate fibers form a wide band which crosses the lateral surface obliquely upward and forward, and obscures the groove which limits the restiform body externally. The cuneate tubercle is distinct. The rhomboid fossa is deep and narrow.

The pons is relatively small. The corpus trapezoideum is very wide and is divided by the pyramids into two lateral parts. The cerebellum is very broad, but is low and also compressed from before backward. Rather more than half of it is overlapped by the cerebral hemispheres. The anterior surface is accurately adapted to the concave tentorial surfaces of the hemispheres and to the posterior corpora quadrigemina and their commissure. The posterior surface is almost vertical and is convex centrally and flattened laterally. The vermis is prominent and in general well defined, although it is connected in its middle part with the hemispheres. The latter are three-sided and consist of four lobules. The anterior peduncles are very short.

The posterior corpora quadrigemina are large, very wide apart, and prominent, and are connected by a curved commissure. The internal geniculate body is large. In the deep interpeduncular fossa are two small bands which indicate the course of the fasciculi retroflexi, tracts which connect the habenular and interpeduncular ganglia. The mammillary body is double. The tuber cinereum is relatively large. The pituitary body is circular and rather small.

The cerebral hemispheres are very broad behind and diminish in width anteriorly; there is a sudden narrowing at the frontal poles, which are flattened laterally. The tentorial surfaces are concave and form a deep cavity which receives the anterior part of the cerebellum. The arrangement of the fissures and gyri is simpler than in the animals previously examined. The chief fissures are as follows:

1. The lateral fissure (of Sylvius) extends upward and backward from the sulcus rhinalis a little behind the middle of the lateral surface of the hemisphere.

2. The ectosylvian fissure has approximately the shape of an inverted u, and curves over the lateral fissure. It is regarded as consisting of three parts—anterior, middle, and posterior (F. ectosylvia anterior, media, posterior).

3. The suprasylvian fissure lies above and approximately concentric with the preceding. It also consists of three parts—anterior, middle, and posterior.

4. The ectomarginal or collateral fissure runs forward on the dorsal aspect of the hemisphere almost parallel with the dorso-medial border. A little in front of the middle of the surface it gives off a short ansate fissure (F. ansata) which runs obliquely inward and forward, and is continued by the coronal fissure.

5. The coronal fissure is the continuation of the ectomarginal. It runs forward and downward, curving around the cruciate fissure, and ends behind the middle of the presylvian fissure.

6. The ectolateral fissure lies between the posterior part of the ectomarginal fissure and the suprasylvian fissure.

7. The entomarginal fissure lies between the anterior part of the ectomarginal fissure and the dorso-medial border. It is often indistinct and not rarely absent.

8. The presylvian fissure begins at the sulcus rhinalis, a little in front of its middle, and curves over the anterior third of the lateral surface of the hemisphere in front of the coronal fissure.

9. The cruciate fissure is the deepest and most characteristic. It cuts deeply into the anterior third of the dorso-medial border and runs almost straight outward. It is continuous on the inner surface of the hemisphere with the calloso-marginal or splenial fissure.

10. The sulcus rhinalis is continued on the tentorial surface of the hemisphere by the occipito-temporal fissure. Anteriorly it is prolonged as the olfactory fissure, which is concealed by the olfactory bulb and tract.

11. The calloso-marginal or splenial fissure is parallel with the splenium and middle part of the corpus callosum on the inner surface of the hemisphere. It is continuous in front with the cruciate fissure and runs downward and outward across the tentorial surface to join the occipito-temporal fissure and sulcus rhinalis. It gives off from its highest part the short lesser or accessory cruciate fissure.

12. The suprasplenial fissure runs almost parallel with the posterior part of the calloso-marginal fissure on the inner and tentorial surfaces of the hemisphere.

The olfactory bulb is large and is strongly compressed laterally; its anterior end projects beyond the frontal pole of the hemisphere. The tract is short and is also flattened laterally. Both contain a narrow cavity which communicates with the lateral ventricle. The pyriform lobe is large and rounded.

The cranial nerves present the following special features which are worthy of notice:

The ophthalmic nerve gives off lacrimal, frontal, long ciliary, ethmoidal, and infratrochlear branches. The lacrimal nerve arises from the ophthalmic at its origin;^[215] its recurrent branch emerges at the orbital ligament and concurs with the zygomatic and frontal nerves in the formation of the anterior auricular plexus. The frontal nerve emerges from the orbit in front of the upper end of the orbital ligament, ramifies in the upper lid and the adjacent skin of the forehead, and sends branches backward to the anterior auricular plexus. The long ciliary nerve accompanies the optic nerve and divides into several branches which pierce the posterior part of the sclera. The ethmoidal nerve gives off internal nasal branches and ends in the muzzle. The infratrochlear nerve runs forward between the internal straight and the superior oblique muscles of the eye and ramifies on the face in the vicinity of the inner canthus.

The maxillary nerve, after giving off the zygomatic, divides into infraorbital and sphenopalatine branches. The zygomatic nerve emerges through an opening in the upper part of the orbital ligament and ramifies in the lower lid and on the adjacent surface of the face. The infraorbital nerves, two in number, divide within the infraorbital canal and after their emergence upon the face, thus forming seven or eight external nasal and superior labial branches. The sphenopalatine nerve gives off lesser and greater palatine and posterior nasal nerves.

The mandibular nerve passes out through the foramen ovale. The superficial temporal nerve divides into auricular, temporal, and malar branches; the last-named crosses the masseter and ramifies with the buccal nerves. The mylo-hyoid nerve is given off from the mandibular nerve almost immediately after the latter emerges from the cranium; it innervates the mylo-hyoideus and digastricus and gives off a branch which turns around the lower jaw, joins the inferior buccal nerve, and ramifies on the lateral surface of the face. The inferior alveolar nerve arises by a common trunk with the mylo-hyoid; it gives off dental branches and terminates in mental and inferior labial branches. The lingual nerve supplies vasodilator and excito-secretory filaments to the submaxillary and sublingual salivary glands; these fibers are derived from the chorda tympani.

The facial nerve divides near the posterior border of the jaw into four branches. The upper branch is the auriculo-palpebral nerve, which divides after a very short course into anterior auricular and zygomatic branches. The latter curves upward and forward across the zygomatic arch toward the eye, and divides into branches which supply the eyelids and nasal region and concur with the frontal and lacrimal nerves in forming the anterior auricular plexus. The superior buccal nerve accompanies the parotid duct across the masseter. The inferior buccal nerve runs forward along the lower border of the masseter and the mandible. The two nerves ramify on the cheek and anastomose with each other and the infraorbital nerves to form a plexus from which branches go to the muscles of the lips and nostrils. The cervical branch runs downward and backward over the submaxillary gland and ramifies in the cervical panniculus; it communicates with the inferior buccal nerve and sends twigs to the parotido-auricularis muscle and the submaxillary space.

The vagus bears a jugular ganglion and a ganglion nodosum. The latter is situated near the superior cervical ganglion on the rectus capitis anterior major and dorsal to the carotid artery; it is fusiform and may be about half an inch (ca. 1 to 1.5 cm.) long in a large dog. In its course in the neck the nerve is inclosed with the sympathetic trunk in a common sheath and is related ventrally to the common carotid artery. The formation of dorsal and ventral œsophageal trunks by the union of the dorsal and ventral divisions of the two nerves takes place at the hiatus œsophageus. The dorsal trunk concurs with branches of the solar plexus in forming the posterior gastric plexus on the visceral surface of the stomach. The ventral trunk ramifies on the parietal surface of the stomach, forming the anterior gastric plexus, from which a considerable branch passes along the lesser curvature to the pylorus. Some special features of the collateral branches are: Two pharyngeal branches are present. The superior pharyngeal branch arises from the vagus above the ganglion nodosum. It passes under the deep face of the carotid artery and descends on the lateral surface of the pharynx to end in the crico-thyroid muscle. It furnishes a root of the inferior pharyngeal branch, and communicates with the pharyngeal branch of the ninth and with the superior laryngeal and hypoglossal nerves. The inferior pharyngeal branch is formed by the union of roots derived from the superior pharyngeal nerve and the ganglion nodosum, together with filaments from the superior cervical ganglion. It crosses the side of the pharynx behind the superior pharyngeal and ramifies on the posterior constrictor of the pharynx and the origin of the œsophagus. It contributes filaments to the pharyngeal plexus, communicates with the recurrent nerve, and supplies twigs to the thyroid gland. The pharyngeal plexus is formed on the lateral surface of the pharynx by branches of the pharyngeal nerves and the communications above described; branches from it innervate the muscles and mucous membrane of the pharynx. The superior laryngeal nerve arises from the ganglion nodosum and descends over the side of the pharynx, crossing beneath the carotid artery and the superior laryngeal nerve. It passes through the thyroid notch and ramifies in the mucous membrane of the larynx. It communicates with the superior cervical ganglion and the superior pharyngeal branch of the vagus, and gives twigs to the hyo-pharyngeus muscle. Immediately after its entrance into the larynx it gives off a large branch which, instead of uniting with the recurrent as in the other animals, has a peculiar arrangement. It runs back near the dorsal border of the thyroid cartilage, gives a branch to the crico-arytenoideus posterior as it passes over that muscle, and continues along the trachea internal to the recurrent nerve. At the thoracic inlet it communicates with the inferior cervical ganglion and continues backward to unite with the vagus at or near the point of origin of the recurrent nerve. Its collateral filaments supply the trachea and concur with the inferior pharyngeal branch in forming a plexus on the cervical part of the œsophagus which innervates that tube.^[216] The depressor nerve is a very delicate filament which arises usually from the superior laryngeal nerve and accompanies the vago-sympathetic trunk to the thorax; its fibers reach the heart through the cardiac nerves. The pulmonary and posterior œsophageal plexuses are highly developed.

The hypoglossal nerve gives off a long branch (R. descendens) which runs downward and backward across the pharynx and larynx, communicates with the ventral branch of the first cervical nerve, and supplies the thyro-hyoid, sterno-hyoid, and sterno-thyroid muscles.

The spinal nerves number thirty-six or thirty-seven on either side, and comprise eight cervical, thirteen thoracic, seven lumbar, and five or six coccygeal.

The brachial plexus (Fig. 487) is derived from the ventral branches of the last four cervical and first thoracic nerves; the root supplied by the fifth cervical nerve is very small. The roots unite at the lower border of the scalenus. The more important special features in the arrangement of the nerves which emanate from the plexus are as follows:

The musculo-cutaneous nerve passes between the coraco-brachialis and the brachial artery and descends in the arm in front of the artery. At the shoulder joint it gives off branches to the biceps and coraco-brachialis, and in the lower third of the arm is connected with the median nerve by an oblique branch. It terminates near the elbow by dividing into a branch for the brachialis and a small cutaneous nerve which passes down over the inner face of the elbow and, inclining a little forward, descends over the deep fascia of the forearm to the carpus.

The radial nerve descends behind the ulnar nerve, gives branches to the extensors of the elbow, dips in between the internal head of the triceps and the accessory head of the anconeus, winds around the arm, and divides between the brachialis and the external head of the triceps into two branches. The deep branch (R. profundus) supplies the extensor and supinator muscles on the forearm. The superficial branch (R. superficialis) emerges upon the flexor surface of the elbow and divides into two branches which terminate by supplying two dorsal digital nerves to each digit, except the fifth, which receives its outer dorsal nerve from the ulnar. The inner branch descends along the inner side of the cephalic vein to the carpus, where it divides into dorsal digital nerves for the first digit and the inner side of the second. The outer branch is much larger. It runs downward on the middle of the front of the forearm and supplies the remaining dorsal digital nerves except that to the outer side of the fifth digit.

The ulnar nerve is as large as or larger than the median, with which it is united for some distance. At the distal third of the arm it separates from the median and passes over the internal epicondyle of the humerus. At the proximal part of the forearm it gives off the dorsal branch (R. dorsalis), which supplies cutaneous twigs to the dorso-lateral surface of the lower part of the forearm and carpus and terminates as the external dorsal digital nerve of the fifth digit. Descending under cover of the flexor carpi ulnaris, the ulnar nerve inclines inward under the tendon of insertion of that muscle and divides into superficial and deep branches. The superficial branch (R. superficialis) runs downward along the outer border of the flexor tendons, gives off the external volar digital nerve of the fifth digit (N. dig. vol. lat. dig. V), and a branch (N. met. vol. IV) which descends in the space between the fourth and fifth metacarpal bones and unites with the deep branch. The deep branch (R. profundus) descends in the carpal canal and divides under the deep flexor tendon into its terminal branches. The smaller of these supply the volar metacarpal muscles. The larger terminals are the three volar common digital nerves (Nn. dig. vol. comm. II, III, IV), which descend along the second, third, and fourth intermetacarpal spaces, subdivide, and concur with the volar metacarpal branches of the median nerve in forming the volar proper digital nerves (Nn. dig. vol. proprii).

The median nerve descends behind the brachial artery, passes over the internal epicondyle of the humerus, then under the pronator teres, and continues in the forearm under cover of the flexor carpi radialis. It gives branches below the elbow to the flexor and pronator muscles, and lower down a palmar branch to the skin on the inner and posterior aspect of the carpus, and terminates between the superficial and deep flexor tendons by dividing into three volar metacarpal nerves (N. met. vol. I, II, III). These descend in the first, second, and third intermetacarpal spaces and unite with the volar common digital nerves in forming volar proper digital nerves. The arrangement of the digital nerves is indicated in the annexed schematic figures.

The lumbo-sacral plexus is formed from the ventral branches of the last five lumbar and first sacral nerves. The more important special facts in regard to the nerves of the pelvic limb are as follows:

The saphenous nerve (Fig. 492) is relatively large, and, in fact, might be considered as the continuation of the femoral nerve. It descends at first in front of the femoral artery, then passes over the lower part of the inner surface of the thigh with the saphenous artery, continues down the leg with the dorsal branch of that vessel, and anastomoses with branches of the superficial peroneal nerve. It supplies cutaneous twigs from the stifle to the metatarsus.

The peroneal nerve separates from the tibial above the origin of the gastrocnemius, runs downward and forward across the outer head of that muscle, passes between the deep flexor of the digit and the peroneus longus, and divides into superficial and deep branches. The superficial peroneal nerve descends the leg along the peroneus tertius and longus, gives off a dorsal branch to the first digit (N. cutaneus dorsalis medialis), and divides at the proximal part of the metatarsus into three dorsal common digital nerves (Nn. dig. pedis dors. comm. II, III, IV). These descend with the superficial dorsal metatarsal arteries and concur with branches of the deep peroneal nerve in forming dorsal proper digital nerves (Nn. dig. ped. prop. dorsales). The deep peroneal nerve passes down the leg with the anterior tibial vessels. It gives twigs to the hock joint and the extensor brevis muscle, and divides into three dorsal metatarsal nerves (Nn. met. dors. II, III, IV); these descend with the corresponding arteries along the intermetatarsal spaces and unite with the dorsal common digital nerves in supplying the dorsal proper digital nerves.