340 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



minor. The common trunk formed by the union of branches from the fifth 

 and sixth lumbar nerves passes laterally as the large femoral nerve. Trace this 

 to the thigh. It courses along the center of the medial surface of the thigh in 

 company with the femoral artery and vein. It innervates adjacent muscles of 

 the thigh and then continues down the shank and foot as the saphenous nerve. 



The obturator nerve arises from the connecting band between the sixth and 

 seventh lumbar nerves and passes obliquely caudad, dorsal to the pubis, through 

 the obturator foramen and into the gracilis and other muscles. 



The seventh lumbar together with the first sacral unite to form a very large 

 trunk, the sciatic nerve. The sixth lumbar and second sacral also contribute 

 small branches to this nerve. Follow the sciatic nerve. It turns dorsally, pass- 

 ing between the ilium and the vertebral column. Thrust an instrument through 

 the place where it turns and dissect where the instrument emerges on the dorsal 

 side of the animal. On separating the muscles at this place the sciatic nerve is 

 exposed. Expose it as near to the vertebral column as possible. The gluteal 

 nerves will be seen separating from the anterior side of the main trunk and pass- 

 ing into the gluteus muscles. (The nerve on the posterior side of the sciatic 

 trunk is the posterior cutaneous, described below.) Follow the sciatic nerve 

 down the leg. After giving off branches into the thigh muscles it divides shortly 

 above the knee into a lateral branch, the peroneal nerve, which passes between 

 the insertion of the biceps femoris and the gastrocnemius, and a more medial 

 branch, the tibial nerve, passing between the two heads of the gastrocnemius. 



The sacral nerves are united by ansae to form the sacral plexus. The first 

 sacral also, as seen above, takes part in the formation of the sciatic nerve. The 

 chief nerves arising from the sacral plexus are the pudendal nerve and the inferior 

 haemorrhoidal. The latter arises in the cat from the point of union of the three 

 sacral nerves and passes to the bladder and rectum. The pudendal nerve arises 

 from the large trunk formed by the union of the second and third sacral nerves 

 and may also in the cat receive a branch from the sciatic. This trunk passes 

 laterally parallel and posterior to the sciatic. From it arises the pudendal nerve 

 which turns toward the rectum and urogenital organs, and the posterior cutaneous 

 nerve which continues laterally into the biceps femoris muscle. It will be found 

 by turning the animal dorsal side up and looking where the sciatic nerve was 

 exposed. The nerve in question lies immediately posterior to the sciatic nerve 

 and enters the biceps femoris. The fourth sacral nerve in the rabbit is of moder- 

 ate size; it passes laterally and then turns to the sides of the rectum which it 

 innervates in common with the pudendal nerve. 



Draw, showing the lumbosacral plexus. 



The foregoing nerves are all the ventral rami of the lumbar and sacral nerves. 

 To see the small dorsal rami of the lumbar nerves proceed as directed for the 

 dorsal rami of the thoracic nerves. The caudal spinal nerves will not be con- 

 sidered. 



