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



digit has but two. Passing from this last one, then, towards the 

 uhiar side we observe tliat 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 rememl)ered, 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 bones 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 vertebrae 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. The pubis (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 tliis 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 cloacce. 



The anterior apex of the united ischia is but H 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 

 fora/nen cordifotme into the two obturator foramina. Either one 

 of these latter is of a subelliptical lorm. Immediately anterior to 

 the pubic sym.physis, 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 mav in some instances chondrify. 

 [b2j 



