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 riin of the cnemial crest of the tibia and the continuous 

 inner margin of the summit of that bone. 



Tlie 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, tlie gluteus also overlaps it, and a delicate connective tissue 

 binds them together. 



The gluteus primus (Plate XLIV. fig. \,gl.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-hke, 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 stru.cture contributed by the extensor femoris lying 

 beneath it, the combined sheatli 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\&ndi 

 the peroneus longus. 



As we would naturally expect, the gastrocnemius muscle (Plate 

 XLIV. fig. 1, g) in Geococeyx is wonderfully well-developed. All 

 three of its heads are strongly defined, and the fleshy belly of the 

 muscle is massive and thick. 



Its external head arises, curiously enough, by two perfectly distinct 

 tendinous slips. One of these, a strong, flat tendon, comes off from 



