DEVELOPMENT OE THE SKELETON OF THE TUATAEA. 45 



With advancing development, the chondrifying centre of the quadrate cartilage 

 extends into the pterygoid and epipterygoid processes in common, and with this 

 replacement there comes about the afore-mentioned rotation, under which the epi- 

 pterygoid process, originally directed backwards and downwards, comes to be upwardly 

 directed, the pterygoid bar being displaced accordingly. On the assumption of this 

 rotation and its definitive position, the quadrate portion elongates and develops two 

 processes — a dorsal or otic process (fig. 4, qj), and a lower process, which appears 

 correlatively with the segmentation off of Meckel's cartilage. Anteriorly its pterygoid 

 portion turns suddenly outwards and expands (c/. espec. PI. III. fig. 6, pg.'). Con- 

 tinuing to elongate, it comes at Stage E. to overlie the pterygoid and the inner half 

 of the OS transversum, tapering to a point. Gaupp describes this cartilage in the 

 Lacertilian as merely extending " in the direction of " the transversum. He points 

 out (Berichte, p. 9) that did it continue forwards it would enter the maxillary region 

 and that of the processus maxillarius posterior (our fourth extranasal process) of the 

 nasal capsule, it would realize the condition occurring in Ranodon and the Anura. 

 With this we fully agree ; but we regard the extension over the transversum as 

 indicative of the retention by Sphenodon of a more approximately batrachian condition 

 than that thus far known for the Lacertilia. 



In Sphenodon the study of the nerves and all possible relationships leaves no doubt 

 that the epipterygoid process is the homologue of the processus ascendens of the 

 batrachian quadrate cartilage, as recognized by Gaupp. He, however, seems to us 

 somewhat in doubt ' as to the actual occurrence in the Lacertilian embryo of a 

 cartilaginous connection between the epipterygoid " Anlage " and the quadrate. 

 In Sphenodon, so far from there being any doubt on this matter, not only are the 

 epipterygoid and quadrate originally prseformed in one continuous cartilaginous tract, 

 but, from Stage E, onwards, the portion of this which, after the establishment of these 

 two bones, remains, begins to ossify by extension of the quadrate centre, to form the 

 characteristic antero-dorsal quadrate lobe (PI. IV. fig. 11), the presence of which 

 accounts for the close relationship of the epipterygoid and the quadrate in the adult. 

 The difference with the reduction of the jugal arch and the liberation and freedom of 

 the quadrate associated in the Lacertilia is one in respect to which the gap between 

 these and the EhynchocephaHa is immensely greater than between them and the 

 Chelonia ^, to say nothing of the Crocodilia and other reptiles possessed of a fixed 



^ Gaupp, E., especially in his paper in Anat. Anz. Bd. vi. 1891, p. 107, and Berichte cit. 1898, pp. 9-11. 



^ We can only express astonishment, mixed with regret, at the gratuitous assumption by Osawa (98 ". 

 p. 102), in seeking to explain away the Giintherian dictum concerning the relationships of the quadrate to 

 the pterygoid, that the latter arises from two ossific centres, of which the hinder has in Sphenodon become 

 co-ossified with the quadrate. There is no trace of any such posterior pterygoid bone actual or potential. 



