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Show •886.] GEOCOCCYX CALIFORNIANUS. 479 front part of the inner marginal rim of the summit of the tibia. This muscle constitutes a powerful auxiliary to the action of the extensor femoris, and it appears to be quite a constant one in the class Aves. The description of the vastus internus completes our account of the musculature of the thigh. A brief recapitulation of them shows us that Geococcyx possesses in this region all of the muscles that we usually find there in birds. The entire group including the ambiens, the femoro-caudal, the accessory femoro-caudal, the semitendinosus, the accessory semitendinosus, and the semimembranosus, so ably introduced into taxonomy by Garrod, are all present and wonderfully well developed. Then we have all three glutei represented, with an ample ex tensor femoris and its auxiliary the vastus internus, a handsome biceps flexor cruris, with its interesting pulley at the back of the knee. Next the two obturators and the gemellus; and finally two powerful adductors, the magnus and longus. W e may now once more direct our attention to the leg, and investigate the muscles there found in its second layer. First among these stands the tibialis anticus (Plate XLIV. fi«s. 1 2, hb.ant). This interesting muscle arises, as most commonly among birds, by two very distinct heads. The under and at the same time the smaller one of these comes off by a tendon from a little pit that is found on the anterior aspect of the external condyle of the femur ; the second or larger portion of the muscle completely covers over the first, except of course its tendon, which extends further up. This latter head arises from a line extending all round within the cnemial crest and the pro- and ectocnemial ridges of the tibia. The fibres of the two heads extend directly down in front of the tibial shaft, at the lower third of which they gradually merge with each other, and finally terminate in a strong tendon, which passing through the oblique fibrous loop, or bridge rather, at the front and lower end of the tibia, pass across the tibio-tarsal joint, to become inserted on the anterior surface of the upper third of the tarso-metatarsus bone, just below its head. The soleus (Plate X L V . fig. 2, so), found at the back of the leg, is another well-developed muscle of this layer in Geococcyx californi-anus. It arises from behind the tibia, on its inner side, and just below the marginal rim of its summit. The fibres at once form a little flat muscle, rather longer in shape than the fish from which it derives its name, and soon terminate at the lower or tail-end in a tendon, This tendon, long and narrow, passes directly down the postero-internal aspect of the leg to become inserted into the dense fascia covering the tibial cartilage at its supero-internal angle. Great care and patience are necessary in the study of the arrangement and distribution of the tendons of the flexors and extensors in the leg and foot of a bird, and to this rule Geococcyx by no means forms any exception. In describing these I will present them in the order that they most conveniently came under m y hand after the removal of the muscles alluded to in the foregoing paragraphs. |