DEVELOPMENT OF THE SKELETON OF THE TUATARA. 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, Z7.p.) at Stage R. Concerning Mehnert’s conclusion, we can 
only add that in Sphenodon the ligament is preformed in cartilage (PI. VI. fig. 7, ¢.i.p.) 
at first of considerable extent, and that with advancing development, correlatively with 
the expansion of the pelvis and widening of the cordiform fenestra, 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 fenestre 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. When viewed from beneath, it is evident that the essential difference 
Fig. 13. Fig. 14. 
Camera-lucida outline sketches of extreme types of the adult pelvis of Sphenodon. 
15, 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. 15) the cordiform fenestra 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-) is about equal 
to that along c-d (fig. 15), 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 
fenestre is equal to that of the symphysis ischii from the vertebral column and‘to the 
transverse diameter of the sacrum. 
For 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 scapule in an extensive 
collection of bones of the Australian Dugong brought home by Professor Haddon. 
F.R.S., from Torres Straits in 1889, now in the custody of one of us. 
