OPHTnALMOSAUEUS. 



exoccipital is short and strongly concave from above downwards — in fact, forming 

 merely a deep groove, in the middle of which is the outer opening of the anterior 

 hypoglossal foramen (XII) above noticed, while anteriorly it passes into the border of 

 the jugular notch. The upper end bears two facets, one roughly triangular and slightly 

 convex for union with the supraoccipital ; this surface looks directly upwards. The 

 other surface looks outwards, upwards, and forwards, while above it is continuous 

 with the supraoccipital surface ; this facet, in some cases at least, was in contact with 

 a corresponding surface on the upper posterior angle of the opisthotic {q. v.), but in 

 other specimens the two elements were probably separated by a pad of cartilage. 



Text-fis. 2. 



'or: 



Esoccipltal aud supraoccipital of OpMlialmosauras : A, right exoccipital from outer side ; B, ditto 

 from inner side ; C, supraoccipital from side ; D, ditto from behind. (E. 2162, J nat. size.) 



a.v.c, depression for anterior vertical semicircular canal ; loc.f., facet for basioccipital ; exo.f., facet for 

 exoccipital ; for., foramen of supraoccipital ; j.for., jugular foramen ; op.f., facet for the opisthotic ; 

 jp., process of supraoccipital projecting into foramen magnum ; pa.f., facet for the parietal ; pro.f., 

 facet for the prootic ; p.v.c, depression for the posterior vertical semicircular canal ; soc.f., facet for 

 supraoccipital ; XII, XII', foramina for the exit of the h3rpoglossal nerve. 



The supraoccipital (text-fig. 2, C & D, also text-fig. 4) is a large fl -shaped bone 

 forming the upper portion of the boundary of the foramen magnum, which is greatly 

 narrowed in this region ; the posterior surface of the bone, as a whole, is gently convex 

 from side to side. The form of the edge bordering on the foramen magnum differs 

 in difl^erent examples ; in some it is simply H-shaped, in others {e. g. that figured in 

 text-fig. 2, D) there is a median process projecting down from the middle of the upper 



