OPHTHALMOSAURUS. 



The description of the form and relations of the bones of the occipital and auditory 

 regions of the skull is rendered difficult by the circumstance that a considerable 

 amount of cartilage persisted throughout the animal's life. The consequence of this is, 

 that not only does the form of the several elements vary considerably according to the 

 degi'ee to which ossification has proceeded, but also, owing to the persistence of 

 the cartilage, actual surfaces of contact between the diff"erent bones are only found in a 



Text-fig. 1. 



cond 



OSS. 



n.c. 



exof 



cond. 



cond". 



Basioccipital and basisphenoid of Ojjhthahnnsaiiriis : A, basioccipital from above ; B, basioccipital 

 from behind; C, basioccipital and basisplienoid from side. (E. 2162, f nat. size.) 



cond., occipital condyle ; ea:o.f., facet for exoccipital ; «.c., neural canal ; op.f., facet for opisthotic ; i^-'^-f 

 posterior part of parasphenoid ; j>-^^-i posterior clinoid processes ; ^n"<./oss., pituitarj' fossa ; pt.p., 

 pterygoid processes ; st.f., facet for stapes ; v.e.p., lower cylindrical processes of basisphenoid. 



few cases, and usually the sepai'ate elements have been displaced and scattered, so that 

 their original position is difficult to make out. The separate elements are first 

 described and then a restoration of this part of the slaiU is attempted. 



The basioccijntal (Pi. I. figs. 13, 14 ; text-figs. 1 & 4) is a short and very massive bone. 

 It forms the whole of the occipital condyle (cond.), which is sessile and forms less thaii 



