THE NERVOUS SYSTEM. av3 
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- 
cutaneous 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. 
