720 THE NERVOUS SYSTEM OF THE PIG 



beneath the peroneiis longus it passes down on the front of the tarsus and meta- 

 tarsus and divides into three branches. The internal and external l^ranches descend 

 as the internal and external dorsal digital nerves on the chief digits. The larger 

 middle branch joins a branch of the dee]) ]ieroneal 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. Ill 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 th(^ internal plantar digital nerve (N. dig. plant, med. dig. Ill) 

 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. Ill 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 liga- 

 ment and to the external small digit, and continues along the outer face of the ex- 

 ternal 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 con- 

 nection 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 separal^le 

 from the first thoracic; the latter is large. There are thirteen pairs of thoracic 

 ganglia. The cceliaco-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 (EUenberger-Baum). It is almost 

 circular in cross-section, except at the enlargements, where it is somewhat flattened 

 dorsoventrally. 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 43/2 ounces). 

 When viewed from al)ove, 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 quadri- 



