14 



MAEIN-E EEPTILES OF THE OXEOED CLAT. 



(see text-figs. 5, A ; 6, A, B), but in no case does it divide the opening of the carotid 

 canal. 



On either side of the pituitary fossa the basisphenoid is produced outwards into the 

 two prominent pterygoid processes {pt.p.), the upper surfaces of which look iipwards 

 and forwards ; at their base there is a stnall perforation {h.c.) leading into the carotid 

 canal and no doubt transmitting a small branch of the internal carotid. The outer ends 

 of the processes are truncated by the facets for the pterygoids looking almost directly 

 outwards and sloping downwards from behind forwards (see fig. 1, C). The ventral 

 surface of the pterygoid processes is roughened for union with the inner plate of the 

 pterygoids, which overlapped and closely united with this part of the ventral face of 

 the basisphenoid, extending back even to the posterior portion of the body, as is shown 

 by the presence of roughened surfaces for union. 



AVhen the basisphenoid is looked at from below (text-fig. 5, A) its posterior border 

 is seen to be nearly a semicircle, while the anterior border is nearly straight, except 

 for the slight projections formed by the ends of the lower cylindi'ical processes {v.c.p.) 



Text-fig. 6. 



p.as. Vic.p. 



Basispbenoid of OpJiiJmhnosaunis ani IcJuhr/osaur us : A and B, basisplienoids of Ophthalmosaurus from below; 

 C, basispbenoid of Iclithrjosauriis from below. (A, E. 2164 ; B, E. 2161 ; C, E. 2063 : f nat. size.) 



i.c.f., internal carotid foramina ; pas., paraspbenoid ; pt.f., facets for pterygoids ; iH.p., pterygoid processes ; 



v.c.p., lower cylindrical processes. 



and by the anterior angles of the pterygoid processes (pt.p.). As already mentioned, 

 the middle of the ventral face is pierced by the internal carotid foramen {i.c.f.). In 

 front of this the adherent posterior end of the paraspbenoid is seen. In diff'erent 

 individuals the degree to which the paraspbenoid overlaps varies (see text-fig. 6). 



