68 THE MUSCULAR SYSTEM OF THE FROG. 
, a. The rectus anticus femoris: forms the middle 
head of the triceps: it arises from the 
ventral border of the posterior third of the 
ilium, in front of the acetabulum: about 
half way down the thigh it joins 
VB. The vastus internus: the preaxial division 
of the triceps: a large muscle arising from 
the ventral and anterior border of the 
acetabulum, and lying in the thigh between 
the sartorius and the rectus anticus. 
vy. The vastus externus: the postaxial division 
of the triceps: it arises from the posterior 
edge of the dorsal crest of the ilium, and joins 
the other two divisions of the triceps about 
the junction of the middle and distal thirds 
of the thigh. 
c. Superficial muscles of the postaxial (apparent dorsal) 
surface of the thigh. 
- i, The gluteus: has been already noticed: it lies in 
the thigh between the rectus anticus and vastus 
externus. 
_ ii, The biceps: a long slender muscle which ‘arises 
from the crest of the ilium just above the 
acetabulum : it lies in the thigh along the inner 
border of the vastus externus, and is inserted by 
a flattened tendinotis expansion into the dista! 
end of the femur and the head of the tibia. ‘ 
iii. The semimembranosus: a stout muscle lying along 
the inner side of the biceps, between it and the 
rectus internus minor, It arises from the dorsal 
angle of the ischial symphysis just beneath the 
cloacal opening, and is inserted into the back of 
the head of the tibia. It is divided about its 
middle by an oblique tendinous intersection. 
iv. The pyriformis: a slender muscle which arises from 
the tip of the urostyle, passes backwards and out- 
wards between the biceps and the semimembra- 
nosus, and is inserted into the femur at the 
junction of its proximal and middle thirds. 
