12 



MAEINE EEPTILES OF THE OXEOED CLAY. 



The basi sphenoid (text-figs. 1, 5, 6, 7) is a stout and very massive bone. Its 

 posterior and most of its upper surfaces are greatly roughened and were obviously 

 thickly covered by cartilage in life. In this region the bone is divided into two 

 prominent comex bosses, separated by a deep median groove running from the middle 

 of the upper anterior edge to the lower posterior border. The posterior faces of these 

 prominences are slightly flattened, or even slightly concave, and were directed towards 



Text-fig. 4. 



Eeconstructioii of the posterior region of skull of Ophihalmosauvus from behind. (About | nat. size.) 



art., articular surface of quadrate; hoc, basioceipilal ; cond., occipital condyle; exo., exoeeipital; for., 

 foramen in supraoccipital ; for.marj., foramen magnum ; ojj., opisthotic ; op./., facet for opisthotic ; 

 p., process of supraoccipital projecting into foramen magnum ; ]ia.f., facet for parietal; p.l.sq., parietal 

 branch of the squamosal ; p.e.a., postero-external angle of the squamosal ; pt., pterygoid ; pt.foss , post- 

 temporal fossa ; q., quadrate ; g.'Asg., quadrate branch of the squamosal; soc, supraoccipital; St., stapes; 

 i.h.sq., temporal branch of squamosal ; XU', foramen for posterior branch of the hypoglossal nerve. 



the corresponding anterior sui-faces of the basioccipital, though probably separated 

 from them by a thick pad of cartilage. The presence of the deep median groove above 

 noticed may be a trace of the original ossification of this bone from two lateral 

 centres. The anterior border of the upper surface is raised into a parr of blunt 

 processes separated by a slight notch : these are the posterior clinoid processes (p.cl.). 

 Beneath them the anterior face of the bone is at first vertical and then slopes slightly 

 backwards, forming the posterior wall of the very large internal carotid foramen {i.cf.), 



