1886.] GEOCOCCYX CALIFORNIANUS. 479 
front part of the inner marginal rim of the summit of the tibia. This 
muscle constitutes a powerful auxillary 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 amdiens, the femoro-caudal, the 
accessory femoro-caudal, the semitendinosus, the accessory semi- 
tendinosus, and the semimembranosus, so ably introduced into taxonomy 
by Garrod, are all present and wonderfully well developed. Then 
we have all three g/wtei represented, with an ample evfensor femoris, 
and its auxiliary the vastus internus, a handsome biceps flewor 
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 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 XLV. fig. 2, so), found at the back of the leg, 
is another well-developed muscle of this layer in Geococcyz 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 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. 
