1886.] 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 semi- 

 tendinosus, and the se»u'?we»«irttnosM«, 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 hanilsome 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. 



We 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. figs. 1, 

 2, tib.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 ectocnemiai 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 XLV. 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 sumniit. 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-interual angle. 



Great care and patience are necessary in the study of the arrange- 

 ment 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 my hand after the removal of the muscles 

 alluded to in the foregoing paragraphs. 



