4 MARINE REPTILES OF THE OXFORD CLAT. 



The pterygoids (pt.) are large bones forming a great part of the palatal surface of 

 the skull. They are of the triradiate structure usual in the group. The anterior 

 rami are very large and their front portion much thickened : externally they unite with 

 the palatines in a nearly straight suture. Anteriorly they seem to have united with 

 the vomers in a complex suture, excluding the palatines from the middle line. In the 

 middle line they meet in front in symphysis for a short distance, then are separated by 

 a narrow anterior interpterygoid vacuity (a.p.v.), behind which they again meet for a 

 short distance (about 4 cm.), but behind they are separated by the anterior part of the 

 parasphenoid, which is thrust in between them for about 8"5 cm. ; behind this the inner 

 edges of the pterygoids curve away from the parasphenoid to enclose the posterior 

 interpterygoid vacuities (p.p.v.), which are about 10-11 cm. long. Behind these openings 

 the pterygoids again meet in median symphysis, beneath the basisphenoid and basi- 

 occipital, which, as noted above, they largely conceal; they also cover, and in the 

 uncrushed condition probably united with, the lower ends of the lateral (pterygoid) 

 processes of the basioccipital. The length of the suture between the pterygoids 

 beneath the basis cranii is about 9 cm. ; the posterior third of this distance bears a 

 strong and prominent ridge, which anteriorly bifurcates, the two branches forming 

 prominent crests which curve outwards through about a quarter of a circle and become 

 continuous externally with the postero-inferior edge of the lateral rami of the bones ; 

 towards their outer ends these crests become thickened with strong tuberosities 

 directed downwards and outwards ; these prominences fit closely against similar 

 projections of the transpala tines (t.p.) in front, forming the downwardly directed 

 processes of the palate seen in Sphenodon and many other reptiles, the outer edge 

 abutting against the inner face of the mandible when the jaws are closed. The 

 anterior border of the lateral ramus is situated a little in front of the level of the 

 anterior ends of the posterior interpterygoid vacuities (p.p.v.) ; it runs out nearly at 

 right angles to the long axis of the skull, and unites in an irregular suture with the 

 posterior end of the palatine. Externally the lateral ramus is overlapped by the 

 transpalatine (t.p.). The outer border of the posterior ramus is greatly thickened and 

 rouuded from above downwards ; this part of the bone is prolonged backwards in a 

 long stout process towards the quadrate, with which it unites closely ; this union may 

 be brought about by the overlapping of the posterior pterygoid process on a corre- 

 sponding process of the quadrate, or may have been directly with the inner edge of that 

 bone ; the arrangement is obscured by crushing, but the former seems the more 

 probable interpretation. The expanded distal end of the paroccipital process (par.p ), 

 as above described, fits closely against the hinder surface of the pterygoid-quadrate bar, 

 which bears a shallow groove for its reception ; the surfaces of contact are smooth and 

 it seems that a certain amount of movement between the bones was possible. The 

 upper surface of the pterygoids near the outer border of the posterior ramus, immediately 

 behind the point of origin of the lateral ramus, bears a long oval surface for the 



