THE MUSCLES OF THE LOWER EXTREMITY. 203 



fully well developed in Geococcyx. All three of its 

 heads are strongly defined, and the fleshy belly of the 

 muscle is massive and thick. 



Its external head arises, curiously enough, by two 

 perfectly distinct tendinous slips. One of these, a strong, 

 flat tendon, comes off from the outer surface of the 

 external condyle of the femur, while the second slip, also 

 strong but somewhat more rounded, arises from the back 

 of the external femoral coudyle, just above the trochlear 

 surface. Between these two tendons of the external 

 head of the gastrocnemius we find the loop for the biceps 

 and the tendon of that muscle itself, the loop being quite 

 intimately attached to the free edge of the outer tendon. 

 Below the loop, these tendons merge with each other 

 and terminate in the commencing fibres that compose 

 the external head of the gastrocnemius proper. 



The internal head of the gastrocnetnius, or what is 

 really the middle head in birds, is quite median in 

 position, and is represented merely by a long, narrow, 

 muscular slip that arises by a delicate, though strong, 

 cord-like, tendon from the middle of the intercondyloid 

 notch of the femur. 



The tibial head of the muscle under consideration 

 is massive in its dimensions when compared with the 

 divisions of origin of the gastrocnemius already described. 

 It arises fleshy from an extensive surface on the inner 

 aspect of the head of the tibia as high up as the marginal 

 boundary of its summit ; and from the muscular fascia 

 surrounding certain of the deep thigh-muscles, which are 

 inserted into the distal end of the femur, and conse- 

 quently are adjacent to the posterior aspect of the head 

 of the tibia. 



At a point about opposite the junction of the upper 

 and middle third of the shaft of the tibia the internal 



