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Show 180 DR. R. W. SHUFELDT ON [Apr. 1, completely filled with fat, which, in this alcoholic specimen now under m y investigation, is of nearly a pure white colour. Feeble fibrous divisions divide it apparently into irregular cells; these merge into a line along the vertebrae, any pair of compartments forming a single longitudinal, fibro-tendinous line, which blends with the tendinous insertional part of the enclosing muscle, that attaches along from vertebra to vertebra in the same locality. I fail to call to m y mind at the present moment any other lizard that is thus supplied with a large store of adipose tissue in its tail, and it would almost seem that it was to serve the purpose of a storehouse commissariat, upon which the entire economy of this reptile could draw in times of need, during its brief period of hibernation in some regions of its range, or, as in torrid Arizona, when the food-supply becomes scarce or difficult for this clumsy lizard to capture. The supracaudal muscle is the direct continuation backwards of the spinalis dorsi, and being but attached to the neurapophyses and neural spines of the tail-vertebrae, it is the smallest muscle of the group. The tendons do not show superficially as do the tendons of the spinalis dorsi along the back, a feature that disappears as the two muscles merge into each other just posterior to the pelvic region. Indeed, when we come to first remove the integuments entirely from the tail of a large alcoholic specimen of Heloderma) the structure is quite devoid of any striking characters, and it is only when we come to use our scalpel that the sulci and other parts are revealed. No tendons or divisions are discernible upon first sight at all. 67. The ilio-caudal continues backwards to the end of the tail the longissimus dorsi and sacro-lumbalis muscles, and it practically in the tail fills the space between the neural spines and the diapophyses of the caudal vertebrae. For the last three fourths of its length this muscle fuses completely with the supracaudal, and the two together combine to form one of the double compartments described above, that are filled with fat. 68. Infra-caudal.-This is the largest muscle of the caudal group, and it ensheaths, on either side, two of the fat compartments alluded to in a previous paragraph. It arises from the posterior aspect of the transverse process of the last sacral vertebra of the same side, from the fascia of the muscles in the immediate post-anal region, from the tuberosity of the ischium by a long, cord-like tendon, and from the margin of the vent itself; it is inserted, seriatim, into the diapophyses and the chevron-bones of all the caudal vertebrae, to the end of the tail. 69. Femoro-caudal.-To expose the next set of caudal muscles we must make a submedian, longitudinal incision through the infero-caudal muscle of one side, following it upon a curve extending down through the other tissues to the tibio-femoral interarticular cartilage, then carefully dissect these muscles out. The one here to be considered arises from the dorsal aspects of the transverse processes of the four proximal caudal vertebrae ; it soon becomes thick |