76 THE MUSCULAR SYSTEM OF THE FROG. 



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. 



vi. The obturator is a deeply situated muscle which 

 arises from the whole length of the ischial sym- 

 physis and the adjacent parts of the iliac and 

 pubic symphyses, and is inserted into the head 

 of the femur close to the glutaeus. 



2. Muscles of the Leg. 



As in the thigh, we distinguish extensor and flexor surfaces, 

 corresponding to the front and back of the leg in man ; and also 

 preaxial and postaxial surfaces, corresponding to the inner and 

 outer sides of the human leg. 



Lay the frog on its belly and commence the dissection from the 

 postaxial surface. 



i. The gastrocnemius is the large muscle forming the 

 calf of the leg : it has two heads of origin, of 

 which the larger arises by a strong, flattened 

 tendon from the flexor surface of the distal e;ad 

 of the femur ; while the smaller head, which joins 

 the main muscle about one-fourth of its length 

 below the knee, arises from the edge of the tendon 

 of the triceps extensor femoris where it covers 

 the knee. The muscle is thickest in its upper 

 third, and tapering posteriorly ends in the strong 

 tendo AcMllis, which passes under the ankle joint, 

 being much thickened as it does so, and ends in 

 the strong plantar fascia of the foot, 

 ii. The 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. 



iii. The tibialis anticus lies on the extensor surface 

 of the leg : it arises by a long thin tendon from 

 the lower end of the femur, and divides about 



