998 MESSRS, B. C. A. WIXDLE ATS'D F. G. PABSONS ON [DeC. 19, 



leg, by vvhicli 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 estensive origin from the shaft 

 of the femur, and in oar specimen of Choloepus it was one of the 

 largest muscles in the hind limb. Its insertion is usually lower 

 than that of the loug head, and may be connected with the tendo 

 Achillis ; moreover it is not always fused even at its insertion with 

 the loug head. Among the Myrmecophugidce the long head, in 

 our specimen of Myrmecophaga (11), rose from the ischium and 

 vk-as inserted into the fascia over the upper part of the fibula. 

 The short head was not so large as \VLi\veBradiipodidai, and instead of 

 rising from the shaft of the femui', it took origin from the insertion 

 of the caado-femoralis, it then crossed deei)ly to the long head, 

 forming an X with it, to be inserted into the gastrocnemius at the 

 point where the tendo Achilhs commenced to exist'. In our 

 specimen of Tamandua (14) there was no femoral head, neither do 

 Eapp nor Cuvier and Laurillard mention one in theirs (15, 16), 

 though Macahster states that it is to be found in this animal. In 

 Cydothurus (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 Dasypodidoi we find no indication of 

 a femoral head in Dasypiis (22, 2-3, 24), Tatusia (25), or CManiy- 

 dophorus (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 fi-om whom we quote. 



Tenuissimus (Bicipiti accessorius). — Eor 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 vertebra; 

 under cover of the ecto-gluteus or caudo-femoralis and passes 

 down, as a narrow ribbon-like muscle, to be inserted witli 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 

 the Bmdypodidce we noticed that the femoral head of the flexor 

 cruris lateralis is always present. In no specimen of Bradyims 

 (1, 2, 4) or Choloepus (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, Myrmecophaya (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 



' MM. Couvreur and Bertaillon desci'ibe an identical arrangement in tlieir 

 specimen (12). 



