1886. ] GEOCOCCYX CALIFORNIANUS. 477 
wards and forwards to the inner surface of the head of the tibia, 
where it becomes inserted, the point of insertion being found above 
that of the semimembranosus muscle, the insertional tendon of which 
overlaps it. 
The semimembranosus (Plate XLIV. figs. 1,2; Plate XLV. fig. 1, 
Sm) in Geococcyz, though thoroughly developed, is rather a slender 
and thin muscle, markedly so when we compare it with the massive 
semitendinosus which overlies it. 
It arises from the outer surface of the ischium, for its posterior 
two thirds, on a line situated a few millimetres above the lower free 
edge of that element of the pelvis. The fibres gradually converge 
as they pass downwards and forwards, to terminate in a very delicate 
and thin ribbon-like tendon, which, passing between the broad tibial 
head of the gastrocnemius and the proximal extremity of the shaft of 
the tibia, becomes finally thereupon inserted on its internal surface. 
The hinder margin of the semimembranosus is free, while its border 
anteriorly is juxtaposed to the posterior edge of the adductors. 
In the bird before us the ambiens muscle (Plate XLV. fig. 1, amb) 
is conspicuously developed. 
It arises from the apex of the prominent prepubic spine of the 
pelvis, and the fibres passing directly down to the inner side of the 
femur, and parallel with that bone, form a strong fusiform muscle. 
As it approaches the patella it terminates in a small flattened tendon, 
which, piercing the fascial envelop of the knee-joint below the 
inferior apex of that sesamoid, passes round the joint, to become 
finally lost to the outer side and opposite the summit of the tibia, 
where some of its tendinous fibres merge with the fibres of origin of 
the flexor perforatus digitorum, or, at least, with one of its divisions. 
The améiens is overlaid by the sartorius muscle, and in the figure 
is brought into view only through the aid of a small dissecting-hook 
and chain, which pull it forwards in order that it may be better seen. 
The femoro-caudal muscle and the accessory femoro-caudal are 
both present and fully developed. 
The femoro-caudal (Plate XLY. fig. 1, f.c) arises, tendinous, from 
the lower posterior border of the pygostyle. It soon becomes fleshy 
and as a narrow, muscular ribbon passes through the tissues over- 
lying the lateral group of caudal muscles proper. Opposite the 
posterior border of the pelvis it expands to form a prettily-shaped 
and compressed spindle, closely covering the obturator externus 
muscle and the side of that bone. As it nears the femur it again 
contracts, receives the fibres of its accessory head, and is finally 
inserted upon the femoral shaft, at the posterior aspect of its prox- 
imal third. 
The accessory femoro-caudal (Plate XLV. fig. 1, afc) arises be- 
neath the overarching part of the postacetabular portion of the ilium, 
just behind the acetabulum and beyond. Its fibres pass obliquely 
downwards and forwards to join with those of the JSemoro-caudal, 
and to become inserted with them into the upper part of the femur 
as already described. 
The obturator ewternus (Plate XLV. fig. 1, 0.e) arises from the 
outer surface of the ischium above the “obturator space,” the 
