180 DR. R. W. SHUFELDT ON [Apr. 1, 



completelj filled with fat, which, in this alcoholic specimen now 

 under my investigation, is of nearly a pure white colour. Feehle 

 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 my 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 svpracaudal 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 entirelyfrom 

 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. 



Q7. 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 ot 

 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. 



6S. 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, 

 seriatini, into the diapophyses and the chevron-bones of all the 

 caudal vertebrae, to the end of the tail. 



G9. Femoro-caudal. — To expose the next set of caudal muscles 

 we must make a submedian, longitudinal incision through the 

 infern-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 pro- 

 cesses of the four proximal caudal vertebrae ; it soon becomes thick 



