38 M ABUSE EEPTILES OF THE OXFOED CLAY. 



inner opening of the jugular foramen (juff-) and separating it from the opening 

 of the ampulla (a.) above noticed. At its lower end the opisthotic is separated from 

 the exoccipital by a deep groove (text-fig. 12, D, s.) both on the lower and inner sides 

 of the bones, but externally complete fusion between them seems to have taken place. 

 The paroccipital process (par.j).) is borne by the upper part of the opisthotic, it arises 

 by a broad base and is oval in section. Towards its middle it contracts and becomes 

 more compressed ; distally it again widens out and is greatly compressed from before 

 backwards ; the posterior face of this expanded portion is gently convex from above 

 downwards, the anterior somewhat concave and possessing a rugose surface (q.f.) 

 apparently for union with another element, the quadrate or quadrate-process of the 

 pterygoid ; the actual distal end of the paroccipital is occupied by a surface that 

 probably was capped by cartilage during life. 



The supraoccipital (s.oc, text-figs. 11, 12, C) is a broad band of bone curved from 

 side to side, the inturned ends being enlarged and lodging a portion of the auditory 

 organ ; there is no evidence that these auditory portions of the bone are at any time 

 separate epiotic elements. The upper edge of the bone is entirely occupied by a large 

 surface (p ; f.), which is nearly flat except on the middle line, where it is raised into a 

 blunt angular projection ; this surface is for union with the parietals. The posterior 

 face of the bone is strongly convex from side to side, while the cranial surface is 

 concave in the same direction. The middle portion of the ventral border, forming the 

 upper border of the foramen magnum, is concave with a slight median projection; 

 external to this are the broad oval surfaces, looking downwards and outwards, for 

 union with the exoccipital-opisthotics ; in the anterior part of this surface there is the 

 opening of the passage lodging the upper portion of the posterior vertical semicircular 

 canal (p.v.c). In front of the surface for the exoccipital-opisthotic there is a large 

 facet (pro.f.) for union with the prootic ; this surface, which looks nearly directly 

 forwards, is excavated by a large recess for the upper part of the posterior and anterior 

 vertical semicircular canals, the latter (a.v.c.) opening on the upper part of the facet, 

 the former (p.v.c), as already noted, on the facet for the exoccipital-opisthotic. The 

 auditory region of the supraoccipital is greatly thickened and seems to have projected 

 considerably into the cranial cavity. 



The prootic (text-fig. 12, A, B) is an irregularly triangular bone; the upper 

 angle is truncated by a surface (soc.f.) for union with the supraoccipital, and bears the 

 opening of the passage for the anterior vertical semicircular canal (a.v.c). The 

 posterior angle is truncated by the surface for union with the opisthotic (exo.op.f.) ; 

 this facet is perforated by the opening of the horizontal semicircular canal (Ji.c). 

 The anterior angle is produced into a process which terminates in a facet, but the 

 nature of this and the anterior facet-like anterior edge of the bone is uncertain ; 

 possibly the process may have reached a facet on the basisphenoid. The body of the 

 bone is hollowed by a large ampullary cavity (a.) which communicates with the 



