1886. ] GEOCOCCYX CALIFORNIANUS. 473 
responding side. The fibres, forming an oblong and rather thick 
muscle, pass downwards and backwards to the region in front of the 
knee. Here it becomes inserted by a special slip of fascia that is 
thrown off and merges with the general fascia surrounding the knee- 
joint ; and, secondly, by a more carneous insertion into the inner half 
of the superior rim of the cnemial crest of the tibia and the continuous 
inner margin of the summit of that bone. 
The sartorius bounds anteriorly the superficial group of muscles 
of the thigh; consequently its anterior border is free. Its posterior 
border above unites quite intimately with the overlapping gluteus 
primus muscle ; while this border below is sharp and free, although 
here, too, the gluteus also overlaps it, and a delicate connective tissue 
binds them together. 
The gluteus primus (Plate XLIV. fig. 1, g/.pr) constitutes that 
great and rather complex muscle which makes up the central fleshy 
portion of the outer aspect of the thigh. It arises by a strong fascia 
from the summit of the coossified neural spines of the anterior sacral 
vertebrae, and by carneous fibres from the outer rim and under 
surface of the whorl-like, overarching portion of the ilium behind ; 
and finally from the contiguous portion of the pelvis over the anti- 
trochanter, between these anterior and posterior origins. In front 
the muscle consists first of a strong layer of semitendinous fascia, 
which closely overlies the gluteus medius muscle beneath it, and 
overlaps the sartorius anteriorly. The posterior origin and mid- 
division become rapidly carneous and more massive as we proceed 
in the direction of the caudal extremity of the body. So that, 
where we find it arising from beneath the overarching part of the 
ilium behind, the muscle fills about one fourth of the convexity there 
formed, the semitendinosus filling the remainder of this curious cavity. 
The fibres of the strong, semitendinous, muscular sheet springing 
from these several origins, or rather along this continuous line of 
origin, now pass, converging as they do so, towards the anterior 
aspect of the knee-joint. The semitendinous portion anteriorly be- 
comes fleshy as it arrives along the outer pelvic margin, with which 
it is quite intimately connected. The hinder division of the muscle 
remains thick and carneous until it comes to the Knee-joint. Here 
all the fibres again become tendinous and fascia-like, and, uniting 
with a similar structure contributed by the evtensor femoris lying 
beneath it, the combined sheath thus formed surrounding the well- 
developed patella, closely invests the front and sides of the knee- 
joint, and is finally inserted all round the anterior and externo- 
lateral borders of the summit of the tibia. 
The most superficial muscles of the leg are the gastrocnemius and 
the peroneus longus. 
As we would naturally expect, the gastrocnemius muscle (Plate 
XLIV. fig. 1, y) in Geococcyx is wonderfully well-developed. All 
three of its heads are strongly defined, and the fleshy belly of the 
muscle is massive and thick. 
Its ewternal head arises, curiously enough, by two perfectly distinct 
tendinous slips. One of these, a strong, flat tendon, comes off from 
