DEVELOPMENT OF THE SKELETON OF THE TUATARA., 61 
proportion to that of the corresponding centralia of the other limb (fig. 12). Bayer has 
suggested that in the presence of the double centrale Sphenodon exhibits a Batrachian 
tendency, drawing attention to the great extent to which the living Urodela are doubly 
centralial. One of us has, with another, attempted to show! that the presence of a 
second centrale carpi is a diagnostic character of the Anura, and this goes to support 
Bayer’s argument. As to centralia, however, Wiedersheim has demonstrated? the presence 
of three in the Axolotl ; and with these facts in mind it occurred to us that the inequality 
in development of the two centralia in Sphenodon might possibly be due to the presence 
of a third, which had fused with the opposite fellow on the opposite sides in the pair 
of limbs under discussion. At Stage Q the condition of the centralia was found to be 
the same as in the normal adult; but in a young specimen belonging to the R. College 
of Science, Dublin, the preeaxial centrale is on each side ossified from two independent 
centres (Pl. VI. fig. 14, pr.c.), and in such a form that while co-ossification of them 
would bring about the condition of the right limb (fig. 12), co-ossification of the 
middle nucleus with the postaxial centrale (po.c.) would result in that of the left. 
Bruhl, for some unaccountable reason, systematically terms * the pisiform of Reptiles 
the “ulnar sesamoid”! Concerning the rest of the proximal carpals and the centralia 
we have nothing to add. 
The distal carpals, stated by Gitinther to be five in number, are by Bayer enumerated 
as four. As he was dealing with a young animal he found only the 4th carpal ossified. 
This is seen to be the case on the left side of our figs. 12 and 13, in which (Stage T) 
the rest of the carpus is still cartilaginous (cf. previous statement on p. 60). Bayer 
believed that the 5th carpale is to be sought in the cartilaginous head of the related 
metacarpal (op. cit. p. 241); but in this he was mistaken, as pointed out by Baur 
in that it is always present and distinct, though small (Pl. VI. figs. 11 to 14). 
We have no variations or other matters to record concerning the phalanges of the 
fore limb. 
The Tarsus.—Ginther describes two proximal and two distal elements, and is doubtful 
about a fifth—the fifth tarsal. He alludes without name to the “ meniscus” of Born, 
which we figure (Pl. VI. fig. 18, mn.). Osawa describes one proximal element, the 
“ proximal tarsale,”’ and four distal—five in all. He regards the meniscus (p. 504) as the 
first tarsale, while Born associates it in the Lacertilia* with the centrale. Both are 
in error, for whereas the meniscus does not appear till Stage S (when all the tarsal 
elements have been formed), the first tarsal arises at Q (fig. 16) as a separate element 
(I.), and at Stage R, when fully chondrified, unites with its metatarsal, The meniscus is 
thus proved to be an accessory element (cf. Born, Morph. Jahrb. Bd. vi. 1880, p. 67). 
* Howes & Ridewood: P. Z. 8. 1888, p. 177. 
* Wiedersheim, R.: Morph. Jahrb. Bd. vi. 1880, p. 581. 
§ Brihl, C. B.: Zootomie aller Thier KI., Wien 1880, pls. 31-34 and 53 & 54, 
* Born, G.: Morph. Jahrb, Bd, ii, 1876, p. 25. 
