70 THE MUSCULAR SYSTEM OF THE FROG, 
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: 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 glutzus. 
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 tts belly eet commence the dissection from the 
postaxial surface. 
L i, The Pe eiveriiit the large muscle forming the 
: calf of the leg : it has two heads of origin, whereof 
the larger one 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 Achillis, 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 internal malleolus, 
lying in a groove in the lower end of the tibia, 
and is inserted into the dorsal surface of the 
astragalus, 
ili.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 
