DEVELOPMENT OP THE SKELETON OF THE TUATAEA. 



59 



ruptedly continuous with the epipubis and hypoischium, Mehnert has denied {op. cit. 

 p. 142) a " skeleto-vicarious " significance to this ligament for Lacerta. Our develop- 

 mental material shows that Wiedersheim was in error, since the ligament is already 

 present (PL VI. fig. 8, U.^y.) at Stage R. Concerning Mehnert's conclusion, we can 

 only add that in Sphenodon the ligament is preformed in cartilage (PL VI. fig. 7, c.i.p.) 

 at first of considerable extent, and that with advancing development, correlatively with 

 the expansion of the pelvis and widening of the cordiform fenestrae, this undergoes 

 a relative reduction with accompanying replacement in fibrous tissue. If Mehnert is 

 correct, the cartilaginous symphysis and the primarily small size of the fenestrse carry 

 Sphenodon so much nearer the Batrachia. 



In the course of our work our attention became arrested by the fact that there are 

 apparently two types of hip-girdle represented in the adult. We append camera-lucida 

 figures of these. AVhen viewed from beneath, it is evident that the essential diiference 



Fig. 13. 



Fiff. 14. 



Camera-lucida outline sketches of extreme types of the adult pelvis of Sphenodon. 

 13, least expanded ; 14, most expanded. Nat. size. 



between them is one of increased length as compared with breadth. In the pelvis of 

 the least expanded type (text-fig. 13) the cordiform fenestrae are more rounded than in 

 the most expanded, in which they appear (fig. 14) angular ; and we find that whereas 

 in the least expanded type the transverse measurement across a-b is about equal 

 to that along c-d (fig. 13), in the most expanded (fig. 14) c-d is greater. We note, 

 however, that in all cases the distance between the opposite limits of the cordiform 

 fenestras is equal to that of the symphysis ischii from the vertebral column and^to the 

 transverse diameter of the sacrum. 



Per want of material undoubtedly mature upon which to base further comparison, 

 we are unable to decide how far this is or is not a sexual matter ; but we are disposed 

 to believe the contrary. The only other case known to us, which is at all analogous, 

 is that of the presence of two still more distinct types of scapulae in an extensive 

 collection of bones of the Australian Dugong brought home by Professor Haddon. 

 P.R.S., from Torres Straits in 1889, now in the custody of one of us. 



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