56 



MAEINE EEPTILES OF THE OXEOED CLAY. 



is fused with the opisthotic, the line of division (text-fig. 12, D, s.) being quite distinct 

 on the surfaces for union with the supraoccipital and basioccipital. The united bones 

 (exo-opisth.) consist of a stout columnar portion forming the sides of the foramen 

 magnum and enclosing part of the auditory organ, and a long paroccipital process 

 (par.p.) projecting outwards and downwards and expanding somewhat at the end. 

 The posterior border of the stout columnar portion is broadly rounded below and 

 bears a backwardly directed facet above (text-fig. 11, fac), looking like a zygapophysis ; 

 this may have articulated with a pro-atlas, or perhaps merely served for the attachment 

 of ligament. The lower end of the combined bones widens out and bears a broad 



Text-fig. 11. 



s.oc. 



Jiarji 



Occipital region of skull of Peloneustes philarchus, from behind. (E. 3803, § nat. sine.) 



e.vo-opisth., exoccipital-opisthotic ; fac, facet like a zygapophysis ; f.m., foramen magnum ; l.p., lateral 

 (pterygoid) process of basioccipital ; oc.c, occipital condyle ; par.p., paroccipital process ; p.f., facet 

 for union with the parietals ; s.oc, supraoccipital. 



surface, convex in the middle, for union with the basioccipital ; the greater part of 

 this surface is formed by the ventral end of the exoccipital (text-fig. 12, D, boc.f.), but 

 the anterior angle, which is separated from the rest by a deep groove, is on the lower 

 end of the opisthotic (boc.f.'). At their upper ends also the united bones widen out, 

 here bearing two facets — a posterior, triangular one, looking inwards and upwards, for 

 union with the supraoccipital (text-fig. 12, D), and a smaller anterior surface directed 

 forwards, upwards, and inwards for the lower end of the prootic (pro.f.). Only a small 

 portion of the posterior surface is formed by the exoccipital, the remainder of the hinder 

 surface and the whole of the anterior being on the opisthotic. In the posterior portion 

 of the opisthotic surface there is the oval opening of the passage which lodged the lower 



