DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 57 



we are disposed to regard the bone as its homologue. It is figured in the macerated 

 state at PL VI. fig. 1, s.mx., and, as remarked by Gaupp, is a membrane-bone. 



The supposed " lachrymal " of Giinther (67. p. 597), accepted by Hofmann J > 

 Seeley (?) 2 , and Credner 3 , has no existence. 



The Prce- and Postfrontal and Postorbital. The two former are proved by their 

 development to be membrane-bones 4 , and examination of PI. IV. fig. 10 shows that 

 they are neither of them compound and that there are no correlated chondro-cranial 

 ossifications. 



The postorbital has the customay relationships of that bone and is very large 5 . 



1 Hofmann, C. K. : Bronn's Klass. u. Ordng. d. Thier-Keichs, Bd. vi. Abth. 3, pi. 66. fig. 5. 



2 Seeley, H. G. : Journ. Linn. Soc., Zool. vol. xii. 1876, p. 184. " In front is a small lachrymal, which is 

 not found in Chelonians." The context is not clear. 



3 Credner, H. r op. tit. p. 510. Baur has pointed out the error here, Amer. Journ. Sci. vol. xxxvii. 1889, 

 p. 311. 



4 "We retain the term praef rental, as one now in general use. It is, however, unfortunate (since it was 

 originally applied by St.-Hilaire, in 1807, to a cartilage-bone, which Cuvier in his 'Legons' defined as trans- 

 mitting the olfactory nerve) that it should have become applied indifferently to various cartilage and membrane 

 bones occurring in the prsefrontal region. A great confusion exists with respect to the modern usage of the 

 term, but it does not materially affect our work. 



5 The study of the postorbital in Sphenodon is intimately bound up with Gunther's work upon the living 

 Crocodilia, which possess but a single so-called " postfrontal." On the basis of comparison with this he came 

 to regard the postorbital of Sphenodon (which, following Stannius, he termed " quadrato-jugal ") as "a 

 detached portion of the postfrontal " (67. p. 598). Baur discovered in 1886 (Zool. Anz. Bd. ix. p. 740) 

 that both postfrontal and postorbital are present in Belodon, and accepted Giinther's conclusion concerning 

 Sphenodon. Their reasoning suggests an origin of the postorbital from the postfrontal, rather than that both 

 bones were originally distinct, and that the presence of one or both is due to variation by co-ossification with 

 age. And, as bearing upon this, we submit the following observation : Cuvier showed that in the Iguana 

 ('Lecons,' t. x. p. 14) there are two bones occupying the region of the postfrontal of other Lizards. He 

 applied to both this term, and figured them as attached side by side to the postorbital process of the frontal. 

 In our own example the hinder bone alone has this relationship, the former being pushed forwards in front of 

 the process named. Comparison with the single " postfrontal " bone present in many Lizards e. y., the 

 familiar backwardly-pointed bone of Yaranus shows this to have the detailed relationships of Cuvier's two 

 " postfrontals " in Iguana, wherefore suspicion arises that it is perhaps compound. That this may be the 

 case is proved by the skull of a young Tupinambis in our possession, in which, as Mr. M. F. Woodward has 

 shown us, two bones are present in its place. Contrary to what happens in Iguana, the postfrontal is alone 

 attached to the frontal and the postorbital to it. This notwithstanding, it follows that the bones described by 

 Cuvier in Iguana are the postfrontal and postorbital, and that they are both represented in the varanoid type 

 (cf. also Gaupp on the embryo Lacerta, in Morph. Arbeiten, Bd. iv. p. 77, pi. vi. fig. 9), We are also 

 indebted to Mr. Woodward for drawing our attention to a skull of the Green Turtle (Chelone mydas) in our 

 Teaching Collection, in which that portion of the " postorbital" suturally conuected with the anterior two- 

 thirds of the frontal is on the left side distinct i. e., an independent postfrontal is present. 



These facts go far to prove that in the Reptilia generally, where either a single " postfrontal" or " post- 

 orbital" is alone present, it may be a compound of these two ; and they certainly suggest that the postfrontal 

 of the living Crocodilia may have gone elsewhere than over to the frontal, as surmised by Baur. 



VOL. xvi. PART i. No. 8. February, 1901. i 



