66 THE MUSCULAR SYSTEM OF THE FROG 



v. 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. 



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 glutaus. 

 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 tJiefrog 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 end 

 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 Achillas, which passes under 

 the ankle-joiiit, 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. 



