52 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE 



region to have been the .first seat in order of time of the development of dermal 

 plates *. ; V- . '' : . - 



Passing. to the ptailate r it 'is seen that at this stage approximation is most marked in 

 front, for while the vomers have met in the middle line, the pterygoids are widely 

 divaricated behind. A noticeable feature is the fact that the palatines, which support 

 the orbital floor, have apparently shared in. the afore-mentioned rapidity of growth. 

 From this stage onwards, the salient feature in progressive development is the closing 

 in towards the middle line of the bones of both the cranial roof and palate, rendered 

 possible by the fact that the most rapid phases in the growth of the brain have now 

 passed. Comparison of PI. III. figs. 11 & 12, and PI. IV. figs. 5, 6, and 8, will 

 render clear the changes undergone in the individual bones during the process, which 

 it is not necessary to describe in words. 



It is at the stage (R) that the parasphenoid first appears, in the form (PI. III. 

 fig. 12, p.s. ; in section in PI. IV. fig. 1) of a minute bony element which would most 

 certainly be lost to sight in ordinary dissection, lying freely beneath the antero-median 

 border of the post-pituitary plate. With advancing development it assumes an arrow- 

 head shape and a more intimate relationship with the basis cranii, fusing by its broad 

 posterior extremity at Stage S with the basisphenoids, and closing the pituitary foramen 

 as it does so by extension anteriorly (PI. IV. fig. 3). 



We have already drawn attention (antea, p. 2) to the interest attaching to this bone. 

 It was overlooked by Giinther, Briihl, and others, and its discovery was first claimed 

 by Fritsch, who believed he had observed it as an independent element 2 . Baur 

 immediately challenged the alleged independence 3 , and gave an accurate account of 

 its limitations in a young individual. Fritsch compared the supposed parasphenoid 

 with that of Hyloplesion, and comparison of his figure of this with that given by 

 Credner (op. cit. p. 513) of the presumed co-ossified basi- and praesphenoids of 

 Palseohatteria at once arouses suspicion by the close similarity in shape of the two ; 

 while further complication arises from the fact that Baur, commenting on Credner's 

 discovery, regards 4 his basi-praesphenoid as a parasphenoid alone. Fritsch for 

 Sphenodon, and Credner for Palseohatteria, were dealing with the compound basi- and 

 parasphenoid, and were therefore in error. Baur was right only in his delimitation 

 of the parasphenoid of Sphenodon. 



The pterygoids, as already remarked, are developed widely apart, apposition in the 

 middle line commencing anteriorly at Stage R, at which (PI. III. fig. 12, pg.) they 

 already reach the vomers i. e., their forward extension is thus recognizable as soon as 



1 Of. Newberry, J. S. : Monogr. U.S. Geol. Survey, vol. xvi. 1889, p. 103, pi. xliv. ; and Jajckel, 0. : Sitzb. 

 Ges. naturf. Fr. 1892, p. 90. 



2 Fritsch, A. : Fauna d. Gaskohle d. Permform. d. Bohmen, Bd. ii. 1889, p. 58. 



3 Baur, G. : Zoolog. Anzeiger, Bd. xii. 1889, p. 45. 



4 Baur, G. : Amer. Journ. Sci. 1889, p. 311. 



