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Show 474 DR. R. W, SHUFELDT ON [Nov. 16, 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 completely 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 confining 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 |