7O THE FROG 



ilium and lies between the anterior and middle heads of the 

 triceps femoris. 



The pyriformis is a slender muscle passing between the 

 origins of the semimembranosus and the posterior head of 

 the triceps. 



(c) The deep muscles of the thigh will be omitted with 

 the exception of the semitendinosus, a long slender muscle 

 lying between the adductor magnus and the gracilis major. 

 It arises by two heads; the anterior head passes through a 

 slit in the adductor magnus and unites with the posterior 

 head in the distal third of the thigh; its tendon of origin 

 gives attachment to a small slip which belongs to the ad- 

 ductor magnus. 



2. The leg (crus). The gastrocnemius lies along the 

 flexor surface of the tibio-fibula, forming the calf of the leg. 

 Its origin is by two heads; distally the muscle ends in the 

 strong tendon of Achilles. Divide and reflect the gastrocne- 

 mius. 



The tibialis posticus lies between the gastrocnemius and 

 the tibio-fibula. 



The tibialis anticus longus lies along the extensor sur- 

 face of the tibio-fibula. It is a slender muscle which divides 

 posteriorly into two slips. 



The peroneus lies on the postaxial side of the leg, be- 

 tween the tibialis anticus longus and the gastrocnemius. 



The extensor cruris is a small muscle lying on the pre- 

 axial side of the anterior half of the tibialis anticus longus. 

 Divide and reflect the latter; this will expose: 



The tibialis anticus brevis. The body of this muscle lies 

 immediately beneath the preaxial slip of the tibialis anticus 

 longus. 



