OCR Text |
Show 998 MESSRS. B. C. A. WINDLE AND F. G. PARSONS ON [Dec. 19, leg, by which its fibres may be traced to the fibula and tibia in their upper ends. In addition to this long and constant mammalian part of the muscle, a femoral origin was found in all the specimens of which we have records. This femoral or short head always seems to have a very extensive origin from the shaft of the femur, and in our specimen of Cholcepus it was one of the largest muscles in the hind limb. Its insertion is usually lower than that of the long head, and may be connected with the tendo Achillis ; moreover it is not always fused even at its insertion with the long head. Among the Myrmecophagidce the long head, in our specimen of Myrmecophaga (11), rose from the ischium and was inserted into the fascia over the upper part of the fibula. The short head was not so large as in the Bradypodidce, aud instead of rising from the shaft of the femur, it took origin from the insertion of the caudo-femoralis, it then crossed deeply to the long head, forming an X with it, to be inserted into the gastrocnemius at the point where the tendo Achillis commenced to exist'. In our specimen of Tamandua (14) there was no femoral head, neither do Rapp nor Cuvier and Laurillard mention one in theirs (15, 16), though Macalister states that it is to be found in this animal. In Cgclothurus (17, 18, 19, 20, 21) all the authorities are agreed as to the presence of the femoral head ; and Meckel (19) says that it is inserted into the outer malleolus, an assertion with which Cuvier and Laurillard agree. In the Dasypodidce we find no indication of a femoral head in Dasypus (22, 23, 24), Tatusia (25), or Chlamydophorus (27, 28, 28 a). In the Manidce a femoral head was found (29, 32, 33), while in the Orycteropodidce no femoral head is recorded by any of the observers from whom we quote. Tenuissimus (Bicipiti accessorius).-For reasons which will appear later, we wish to contrast the presence or absence of this muscle with the condition of the long head of the last described muscle. First, however, we call attention to the fact that in most mammals the tenuissimus arises from the anterior sacral vertebrae under cover of the ecto-gluteus or caudo-femoralis and passes down, as a narrow ribbon-like muscle, to be inserted with the lowest fibres of the flexor cruris lateralis, i. e., with those fibres which most nearly attain the ankle. As these fibres are often inserted into the tendo Achillis or gastrocnemius, it is clear that this will not be an uncommon insertion for the tenuissimus. In tbe Bradypodidce we noticed that the femoral head of the flexor cruris lateralis is always present. In no specimen of Bradypus (1, 2, 4) or Cholcepus (8, 9, 10) is the presence of a tenuissimus mentioned, while in our specimens (1, 8) we specially looked for it and can definitely state that it was absent. Amongst the Myrmecophagidce., Myrmecophaga (11, 12) has a short head for the flexor cruris lateralis, which, instead of rising from the femur, comes from the surface of the caudo-femoralis. This animal has no tenuissimus. Our Tamandua (14) had a typical mammalian 1 M M . Oonvreur and Bertaillon describe an identical arrangement in their specimen (12). |