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Show 1S99.] THE MYOLOGY OF THE EDENTATA. 999 tenuissimus, but no short head of flexor cruris lateralis, and the same condition existed in Cuvier and Laurillard's specimen (16). All the specimens of Cyclothurus had femoral heads for flexor cruris lateralis, but in none of them is a tenuissimus recorded. In the Dasypodidce a short head of flexor cruris lateralis is never found, but in Dasypus (22, 23) and Tatusia (25) the tenuissimus was present, though not in Chlamydophorus (27, 28, 28 a). The Manidce have a femoral head to the flexor cruris lateralis. In two cases (29, 33) there was no tenuissimus, in the others its presence is not mentioned. The Orycteropodidce have no femoral head to the flexor cruris lateralis, but Galton (35) evidently found a tenuissimus in his specimen, though he calls it the second part of the semimembranosus. The fact that these two muscles, the short or femoral head of the flexor cruris lateralis and the tenuissimus, never in our records and dissections have been found to co-exist, made us suspect that the two muscles might be identical. This suspicion was strengthened when we noticed how similar the insertion of the two muscles was, the origin alone differing. The condition met with in our specimen of Myrmecophaga (11), as well as iu that of M M . Couvreur and Bertaillon (12), makes us think that the caudo-femoralis acts as a " muscle-slide," down which the origin of the tenuissimus slips until it reaches the shaft of the femur, when it becomes a short head of the flexor cruris lateralis. Does this explain the morphology of the femoral head of the human biceps femoris ? We are not prepared to commit ourselves to a definite statement of opinion until we have examined into the matter more fully, as we propose to do at a subsequent time, but so far as tbe evidence before us goes we are inclined to answer the question in the affirmative. Quadriceps extensor cruris.-In all our dissections of Edentates we found the rectus rising by one broad head from the dorsal and cephalic margins of the acetabulum, and fusing more or less with the capsule of the hip-joint. Most of the other writers who give any details of the origin of this muscle speak of it as single-headed. Humphry, however, states that in Oryeteropus (36) its origin is as in M a n ; though Galton, in his description of the same animal (35), says that the rectus rises from the superior and posterior margins of the acetabulum, not mentioning the fact that there are two distinct heads. Our experience of myology makes us think that in the Edentata, as in most mammals, there is one broad head, and that in M a n this head becomes differentiated into two as an adaptation to the erect position. In other words, we believe that in the Edentates both the acetabular and iliac heads of the rectus are present, but that they are fused or not yet differentiated. Of the deeper parts of the quadriceps there is little to say beyond the fact that the quadricipitis lateralis (vastus externus) is always very large in proportion to the mesialis (vastus internus). In Chlamydophorus (27) Macalister found an extra head to the lateralis rising from the ilium beneath the origin of the super-ficialis (rectus femoris). This was not seen in the other two |