192 . Systematic Paleontology 



Anteriorly, the bone united with its fellow, thinning out for the exit 

 of the olfactory lobe. Below is the large, rounded optic foramen, while 

 in the middle of the bone, running from above downward, is a long, 

 narrow foramen, showing a tendency to be constricted into three aper- 

 tures, probably for the exit of the third and fourth cranial nerves, and 

 possibly for the anterior carotid artery. Behind the long foramen is a 

 sharp crest, which evidently buttressed the post-orbital, as in Morosaurus. 

 Posteriorly, just below the origin of this crest is part of the large fora- 

 men for the fifth cranial nerve. The dimensions of the bone are as 

 follows : 



Fore and aft diameter 48.6 mm. 



Vertical diameter 40.0 mm. 



The supra-occipital (E'o. 5692, U. S. ISTational Museum) again agrees 

 closely in shape with that of Morosaurus, forming the upper portion of 

 the foramen magnum. It differs from that of Morosaurus in forming a 

 relatively broader arch to the roof of the brain case. 



Anteriorly, there is, on either side, the sutural surface for articulation 

 with the parietal, but between these articulations there is a finished an- 

 terior border which may have been edged with cartilage but which shows 

 no sutural indication. In front of this area a fontanelle must have been 

 situated, probably of a temporary character, and not corresponding to 

 the interparietal or pineal foramen. It must, of course, be borne in mind 

 that we are dealing with a very immature animal. 



The principal points wherein the bone differs from that of Morosaurus 

 other than that above mentioned are in proportions and in the curves 

 of the various surfaces; the present bone being slightly convex from 

 side to side while that of Morosaurus is decidedly concave. 



DIMENSIONS 



Width 63.0 mm. 



Fore and aft diameter r 33.7 mm. 



Greatest depth 27.0 mm. 



Width of foramen magnum 18.5 mm. 



Greatest width of brain case 32.2 mm. 



