998 MESSRS. B. C. A. WIXDLE ASX) T. G. PARSOXS ON [DeC. 19, 



leg, by which its fibres uiay be traced to the fibula and tibia in 

 their upper ends. In addition to this long and constant 

 niammalian 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 Choloepus 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. Amoug the Ali/rmecoj^haijidie the long head, in 

 our specimen of 2I)/rmeco2)haga (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 mtheBradiipodidie, and 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 whei'e the tendo Achillis commenced to exists In our 

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

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

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

 Cyclothurus (17, 18, 19, 20, 21) nil 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 DasypodidLcK we find no indication of 

 a femoral head in Dasmjus (22, 23, 24), Tatusia (25), or Chlamy- 

 doijJiorus (27, 28, 28 a). In the Manidce a femoral head was 

 fouud (29, 32, 33), while in the Orycteropodidce no femoral head is 

 recorded by any of the observers from whom we quote. 



Tenuissinnis (Bicipiti accessor ius). — 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 vertebra; 

 under cover of the eeto-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., w ith those fibres 

 w^hich most nearly attain the ankle. As these fibi'es are often 

 inserted into the tendo Achillis or gastrocnemius, it is clear that 

 this will not be an uncommon insertion for the tenuissimus. In 

 t])e Bradi/podidif we noticed that the femoral head of the flexor 

 cruris lateralis is always present. In no specimen of Bradyj^jits 

 (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 tlie 

 Myrmecophagidce, Mynnecophaja (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 describe an identical arrangement in tlieir 

 specimen (12). 



