THE NERVOUS SYSTEM 237 



The ulnar nerve (Fig. 114) is derived from the eighth cervical 

 and first thoracic. It courses with the brachial artery to the 

 middle of the humerus, where it turns caudad to pass between 

 the olecranon process and internal condyle of the humerus. It 

 is here subcutaneous and furnishes the sensation experienced 

 when one strikes what is popularly called his ''funny bone," but 

 what is really the ulnar nerve. It then passes down the ulnar 

 side of the forearm, supplying some of the flexor muscles, and 

 finally divides to supply the fourth and fifth digits. The ven- 

 tral branches of the remaining thoracic nerves encircle the body, 

 supplying the muscles and skin of those regions. 



The lumbar plexus (Fig. 115) is composed of the anastomos- 

 ing of the ventral branches of the four caudal lumbar nerves. 

 As in the cervical and thoracic nerves, the lumbar nerves divide 

 into dorsal and ventral branches immediately without the inter- 

 vertebral foramen. The former supply the muscles and skin of 

 the back. In order to display the lumbar nerves, the entire 

 ventral and lateral abdominal wall should be cut away and 

 the specimen securely nailed to the tray on its back. The 

 adipose tissue and muscles lying on either side of the bodies of 

 the lumbar vertebrae must be carefully picked away until the 

 roots of the nerves are apparent. They may then be easily 

 followed distad. 



The first three lumbar nerves of the cat are represented in 

 man by the ilio-hypogastric and ilio-inguinal. The first nerve 

 supplies the rectus muscle and skin of the abdomen. This 

 nerve and the two next described are scarcely as large in diam- 

 eter as an ordinary pin. The ventral branch of the second lum- 

 bar nerve divides into two branches, and supplies the skin of the 

 caudal part of the abdomen, and structures in the inguinal 

 region. The ventral branch of the third lumbar nerve supplies 

 the inguinal region and is also distributed to the transverse and 

 rectus muscles. The fourth lumbar nerve divides into two 

 parts, one of which is the genito-crural (genitofemoral) nerve, 

 supplying the skin and other structures of the ventral abdominal 

 wall and thigh, the other branch together with part of the fifth 



