xiii.] THE FROG. -229 



a. The pectineus: it lies at the upper part of the 

 thigh immediately internal to the vastus inter- 

 nus: it arises from the front of the pelvis, 

 close to the symphysis, and is inserted into 

 the anterior surface of the distal half of the 

 femur. 



/?. The adductor brevis (2. d. y) : it lies along the 

 inner side of the pectineus and arises and 

 is inserted close to it. 



y. The semitendinosus : this is a long slender 

 muscle lying beneath the rectus internus major 

 and bifurcated at its upper end : its two heads, 

 thus formed, arise, one (anterior head) from 

 the pelvis between the ischial symphysis and 

 the acetabulum; the other (posterior head) 

 from the ischial symphysis : the muscle termi- 

 nates below in a rounded tendon which is 

 inserted along with the sartorius. 



4. Turn the frog over on to its belly, and remove the 

 skin from the back of the limb. 



The muscles on the back of the thigh. These are : 



a. The triceps femoris : a very large muscle on the 

 outer side, divided above into three heads, which 

 are often regarded as separate muscles, viz. 



a. The vastus internus: the anterior division, 

 which has been already seen on the front of 

 the thigh. (2. d. r?.) 



ft. The vastus externus : the posterior division ; 

 it arises from the hinder edge of the iliac 

 bone. 



