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Show 228 DR. R. W. SHUFELDT ON [Apr. 1, digit has but two. Passing from this last one, then, towards the ulnar side we observe that they stand 2, 3, 4, 5, 3. Taken as a whole, this pectoral limb of Heloderma is a very well-developed one, and in the absence of the intermedium it agrees with the Crocodiles ; it will be remembered, however, that aside from this point these latter have a very differently constituted carpus from the one we have just described in the Lizard before us. On the Pelvis and the Pelvic Limb. In its general characters and in its outlines, the pelvis oi Heloderma agrees with that part of the skeleton as it is found in all ordinary Lizard-forms known to us. The acetabulum is extensive but not very deeply excavated, it being formed in the usual way by the union of the three hones composing the os innominatum. The ilium contributes its share to the dorsal third of the acetabulum, and from this expanded portion it at first passes upwards, then curves upon itself to pass almost directly backwards, and only slightly upwards. All this last part of the ilium is stout in character and rod-like in form, being compressed from side to side. The manner in which it is seized by the two sacral vertebras has already been described above when speaking of the vertebral column. Posteriorly the ilium is carried nearly a centimetre beyond its sacral articulation, terminating behind in a free blunt point. Hhe j)ubis (or the pubic bone) represents the smallest element of either half of the pelvis, it being the antero-ventral one and forming the antero-ventral part of the acetabulum. Dorsally it is nearly straight from the last-named point to the symphysis 'pubis, while from side to side it is convex. In the same direction, ventrally, it is somewhat excavated. At its usual site it is pierced by the foramen for the passage of the obturator nerve, while just anterior to this point a fairly well-developed pectineal process is to be seen. More irregular in form than either the ilium or the pubis, the ischium completes the postero-ventral part of the acetabulum. To describe it, one might say that it is composed of a broad flattened arm that passes downwards and inwards from the acetabulum, to merge, ventrally, into a quadrilateral plate, its second part; and that the mesial border of this plate forms the line of the symphysis ischii. This latter is slightly separated by a slip of calcified cartilage, and this is continued posteriorly, beyond the symphysis, into the ventral wall of the cloaca, as a small os cloacae. The anterior apex of the united ischia is but 5 millimetres distant from the posterior apex of the united pubic bones, and this is spanned by an azygos ligament, that, as usual, divides the not large foramen cordiforme into the two obturator foramina. Either one of these latter is of a subelliptical form. Immediately anterior to the pubic symphysis, we find a small nodule of cartilage that has been designated as the prepubis. And this is connected with the mesial pubo-ischiadic ligament, and even the hinder portion of this latter may in some instances chondrify. |
