1899,] THE MYOLOGY OF THE EDENTATA. 999 



tenuissiinus, but no short liead of flexor cruris lateralis, and the 

 same condition existed in Cuvier and Laurillard's specimen (16). 

 All the specimens of Oi/clothums had femoral heads for flexor 

 cruris lateralis, but in none of them is a tenuissiraus recorded. 

 In the Dasypodida' a short head of flexor cruris lateralis is never 

 found, but in Dasijpus (22, 23) and Tatasia (25) the tenuissiraus 

 was present, though not in ChJanujdopJiorus (27, 28, 28 a). The 

 Manid(e have a femoral head to the flexor cruris lateralis. In two 

 cases (29, 33) there was no tenuissiraus, in the others its presence 

 is not mentioned. The Ori/cterojjodkhe have no femoral head to 

 the flexor cruris lateralis, but Graltou (35) evidently found a 

 tenuissiraus 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 

 tenuissiraus, never in our records and dissections have been found 

 to co-exist, raade 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 Myrmeco- 

 2yha(/a (11), as well as iu that of MM. Couvreur and Bertaillon 

 ( 1 2), raakes us thiuk that the caudo-femoralis acts as a " muscle- 

 slide," down which the origin of the teuuissiraus slips until it 

 reaches the shaft of the feraur, 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 the evidence before us 

 goes we are inclined to answer the question in the affirmative. 



Qaadriceps 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, howe\er, states that in Orycteropus (36) its origin is as 

 in Man ; 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 Man this head becomes differentiated into two as an 

 adaptation to the erect position. In other word?, 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 

 Chlamydojihorus (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 



