COPE ON GEOLOGY AND VERTEBRATE FOSSILS 589 



dyle, so that the posterior portion of the skull rose like the abutmeut of 

 an arch from the vertebral column. This structure also contracts the 

 space occupied by the brain, a deficiency wliich is compensated by its 

 elongation forward. 



The basiocci2)ital iSj in its axial portion, exceedingly short, the condyle 

 and its peduncle including two-thirds of i^s length. In front of this is 

 a considerable expansion, consisting of two huge cup-shaped postero- 

 inferior processes, which spread out laterally- and inferiorly from the 

 neck of the condyle, partially concealing it from an inferior view. They 

 are separated bj' a deep emargination immediately below the condyle. 

 These processes are doubtless the insertions of powerful muscles, and 

 appear to be homologous with those found on each side of the basis era- 

 nil anterior to the occipital condyle in the Emeu. Their borders are 

 separated from those of the exoccipitals by a deep notch on each side. 

 This element may be the true sphenoid, although sutural distinction 

 from the basioccipital is not clear. (See Figs. 7, 7a.) 



The exoccipitals have an aliform lateral expansion, which extends 

 beyond the lateral walls of the brain-case. Each one consists of two 

 principal ribs, which terminate in projections which are separated by a 

 concave thin margin. The anterior is curved forward, the posterior is 

 straighter, and is directed outward and a little backward. The supra- 

 occipital is narrow, and is bounded by an elevated ridge on each side, 

 which approach each other upward. The postero-superior face is 

 deeply concave, and is divided by a strong median carina, or crest, of 

 the same elevation as the lateral crests. The foramen magnum is rela- 

 tively large, and is a little higher than wide. It is probable that the 

 supraoccipital bone does not form part of its border, although, a very 

 small portion having been broken from its posterior edge, the question 

 is not positively decided. The occipital condyle is relatively large, and 

 consists exclusively of the basioccipital bone. It is a portion of a globe? 

 the superior convexity being interrupted by a small plane. It is sup- 

 ported on a short neck, on the superior face of which are two lateral 

 shallow concavities. 



Tho, presplienoid or splienoid bone is simple and of remarkable length, 

 resembling that of a Bird or Snake rather than that of a Lizard. It has 

 no. posterior lateral processes corresponding to those in front of the basi- 

 occi])ital bone, but embraces the base of the former equally all round 

 by a squamosal suture. The notch separating the occipital processes is 

 continued as a wide groove, which rapidly contracts to an acute termi- 

 nation on the posterior part of the basisphenoid bone. It is bounded on 

 each side by an elevated ridge. These are bounded externally by an open 

 groove on each side, which unite farther forward on the basisphenoid. 

 These are in turn bounded on the outer side by an obtuse ridge, which 

 are not continued on the sphenoid. The median portion of the basi- 

 sphenoid is convex from side to side. The anterior portion is narrower, 

 and the cranial cavity is here strongly compressed. (See Fig. S.) 



