252 THE BIOLOGY OF THE FROG CHAP. 



thigh ; the muscle is inserted by a narrow tendon into the 

 preaxial side of the proximal end of the tibia. It adducts 

 the femur and flexes the leg. 



The pyriformis, a short, slender muscle extending from 

 the tip of the urostyle to a short distance beyond the head 

 of the femur. . It lies between the semimembranosus and 

 the posterior head of the triceps. It pulls the urostyle to 

 one side and draws the femur dorsally. 



The iliacus externus arises on the outer side of the dor- 

 sal crest of the ileum from the anterior third to within a 

 short distance from the posterior end. It extends back- 

 ward, passing between the middle and posterior heads of 

 the triceps to be inserted on the posterior side of the head 

 of the femur. It rotates the femur forward. 



The iliacus interims arises from the ventral border of 

 the ileum, a little in front of the anterior spine. In the 

 anterior position of its broad origin its fibers run below the 

 lower margin of the ileum to be attached to the median sur- 

 face. Its insertion extends from the hip joint to about the 

 middle of the femur. This muscle is broad and flat, and 

 extends between the middle and anterior heads of the 

 triceps ventral to the iliacus extermis. It draws the thigh 

 forward. 



There are several smaller muscles around the head of the 

 femur ; viz. the pectineus, obturator externus, obturator 

 internus, ileo-femoralis, quadratus femoris, and gemellus, for 

 a description of which the student is referred to Ecker's 

 " Anatomy of the Frog." The muscles of the leg, or crus, 

 are as follows : - 



The gastrocnemius which has been mentioned above is 

 the largest muscle of the leg. It arises by two heads, the 

 larger one from a tendinous arch which extends from the 

 posterior side of the distal end of the femur to the head 



