THE NERVOUS SYSTEM. 213 



pierces, and then divides into several branches, one of which 

 is the saphenous, passing subcutaneously along the medial 

 aspect of the leg. The other nerves supply the muscles of 

 the thigh on the cranial and medial aspect. The obturator 

 nerve is composed of branches from the sixth and seventh 

 lumbar. It is smaller than the preceding, and passes 

 through the obturator foramen to supply the obturator, ad- 

 ductor, gracilis and pectineus muscles. 



The sacral plexus is formed of the three sacral nerves 

 with branches from the sixth and seventh lumbar nerves. 



The great sciatic nerve is composed mainly of the ventral 

 branches of the seventh lumbar and first sacral nerves. It 

 usually receives accessions from the other sacral nerves and 

 the sixth lumbar. The great sciatic is the largest peripheral 

 nerve in the body. It passes caudad from its origin around 

 the greater sciatic notch and thence along the caudal aspect 

 of the thigh to the popliteal space, where it divides into the 

 internal and external popliteal nerves. The former con- 

 tinues down the caudal side of the tibia as the posterior 

 tibial nerve to the internal malleolus, where it divides into 

 internal and external plantar nerves, which supply the digits. 

 The external popliteal or peroneal nerve extends to the outer 

 cranial aspect of the leg, where it divides into the musculo- 

 cutaneons and anterior tibial nerves. The former extends 

 between the extensor longus'digitorum and peronei muscles 

 to its ramification on the dorsum of the foot. It supplies 

 the skin along its course and the peronei muscles. The 

 anterior tibial nerve passes down on the cranial aspect of 

 the tibia beneath the extensor longus digitorum muscle to 

 the tarsal region, where it anastomoses with a branch of the 

 external cutaneous, and supplies the skin, tibialis anticus, 

 and the extensor muscles. 



The lesser sciatic nerve comes chiefly from the second and 

 third sacral nerves. It supplies the region of the anus and 

 the biceps muscle. 



