FOSSIL REPTILES. 355 



The lower occipital is very thick, and terminated behind by 

 a very gross tubercle, which serves nearly alone for the articu- 

 lation with the atlas, for the lateral occipitals scarcely have 

 any sensible share in this. Its inferior face is convex, not 

 concave as in the lizards, nor has it the lateral apophyses 

 which theirs possesses, so that it takes no part in the parietes 

 of the external ear, or of the cavity. This is a marked rela- 

 tion with the tortoises. 



Another still more sensible relation is the division of the 

 lateral occipitals. These bones, articulating with the upper 

 and lower occipitals, have, externally and above them, a void, 

 and present conjointly with the upper occipital an indented 

 edge, announcing a suture, which cannot be filled but by an 

 external occipital analogous to that of the tortoise, and which 

 occupies the space which the os petrosum leaves behind it. 



The sphenoid is as thick as the lower occipital. A trans- 

 verse crest of its upper face distinguishes the cerebral region 

 from that in which the pituitary gland reposes. The last is 

 pierced at the bottom by a canal which goes obliquely back, 

 and goes out at the lower face of the bone by one or two 

 holes, according to the species. In front, the sphenoid gives 

 out a very long point, to support, as in the lizards, the vertical 

 and membranous partition between the orbits. Laterally, it 

 presents on each side a truncated apophysis, to touch the ptery- 

 goid bone, and a little further back, a rough face for its j unc- 

 ture with the os petrosum. In all these relations it resembles 

 exactly the sphenoid of a lizard. The os petrosum is articulated, 

 relatively to the sphenoid, in such a manner that the pterygoid 

 •must proceed nearly parallel to the external face of the former, 

 and that if they do not actually touch, as in the tortoises, at 

 least very little space must be left between them. The exter- 

 nal face of the petrosum is simple, and a little convex, like that 

 of the lower occipital, and has not the crest, which, in the 

 iguana, protects the concavity, at the bottom of which is the 

 fenestra ovalis — an additional reason for believing that the 



2 A 2 



