474 DR. R, W. SHUFELDT ON [NoV. 1 6, 



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 condyle, 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 gastrocnemius, 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 consequently 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 and tibial heads of the 

 gastrocnemius merge with each other, while between their free edges 

 above passes the exceedingly delicate tendon of the semimembranosus 

 muscle. 



All of the fibres of this complicated origin of the gastrocnemius 

 muscle now converge and pass directly down the back of the leg of 

 the bird. They also merge with each other in such a manner that, 

 were we to examine the muscle at about the middle third of the leg, 

 we would find it composed of two well-defined bellies, rather thin, 

 nearly of equal size, united somewhat firmly by an intervening fascia, 

 and each being convex on their superficial aspect and the reverse on 

 their under sides, which concavity accurately moulds itself to the 

 deeper layer of muscles of the leg, which the gastrocnemius com- 

 pletely covers. 



At the lower fourth of the tibial shaft the fibres terminate in a 

 broad, flat, and glistening tendon, which passes flat-wise over the 

 shallow and longitudinal groove of the tibial cartilage, at which 

 point the tendon is considerably thickened. Next, crossing the 

 tibio-tarsal joint, it becomes internally attached to the hinder surface 

 of the hypotarsus of the metatarsal bone, below which protuberance 

 it finally merges into the deeper layer of the podothecal sheath con- 

 fining the flexor tendons. 



The peroneus longus (Plate XLIV. fig. 1, p.l) arises from the 

 entire free margin of the cnemial crest in front of the head of the 

 tibia, and by somewhat specialized, though delicate, tendons, one each 

 from the apices of the pro- and ectocnemial processes of the same part 

 of the bone. These latter tendons pass down on the under surface 



