84 GENERAL BIOLOGY 



passes down the thigh beneath these muscles, and is inserted into the 

 back of the proximal half of the femur. It draws the thigh forward. 



5. The quadratus femoris is a small muscle on the back of the 

 upper part of the thigh ; it arises from the ilium above the acetabulum, 

 and from the base of the iliac crest; it lies beneath the pyriformis and 

 behind the biceps, and is inserted into the inner surface of the proximal 

 third of the femur between the pyriformis and the ilio-psoas. 



6. The obturator is a deeply situated muscle which arises from 

 the whole length of the ischial symphysis and the adjacent parts of the 

 iliac and pubic symphyses, and is inserted into the head of the femur 

 close to the gluteus. 



Innervation : Branches and twigs from sciatic nerve and 

 plexus. 



5. Muscles of the Leg or Shank. 



e. g. (1) Peroneus, a long muscle which arises from the end 

 of the femur, lies along the side of the tibio-fibula, and is inserted into 

 the end of the tibia and the calcaneum ( ). It ex- 



tends leg and foot and flexes foot. 



Innervation : Peroneus nerve. 



(2) Gastrocnemius ( ), a large, spindle- 

 shaped muscle which forms the "calf." It arises from the hinder side 

 of the end of femur and tapers into the long tendo Achillis, which passes 

 under the ankle joint and ends in the sole of the foot. It straightens the 

 foot on the shank. 



Innervation : Tibialis nerve. 



(3) Tibialis anticus, arising from the front of the femur by a 

 long tendon, lying in front of the shank, and dividing into two bellies, 

 which are respectively inserted into the astragalus and calcaneus. It 

 bends the foot on the shank. 



Innervation : Peroneus nerve. 



(4) Tibialis posticus arises from the whole length of the flexor 

 surface of the tibia; it ends in a tendon which passes round the inner 

 malleolus ( ), lying in a groove in the lower end 

 of the tibia, and is inserted into the dorsal surface of the astragalus. It 

 extends the foot when flexed, and flexes foot when extended. 



Innervation : Tibialis nerve. 



(5) Extensor cruris lies along the preaxial side of the tibialis 

 anticus, partly covered by this and partly by the strong fascia of the 

 leg. It arises by a long tendon from the preaxial condyle of the femur, 

 runs in a groove in the upper end of the tibia, and is inserted into the 

 extensor surface of the tibia along nearly its whole length. It extends 

 the foot. 



Innervation : Tibialis nerve. 



6. Muscles of the Foot. 



These, just as the muscles of the wrist and hand are many and 



