14 THE MORPHOLOGY OF THE SKULL 



"A cast of the brain cavity shows fairly Avell all parts posterior to the fifth pair 

 of nerves, and^the hypophysis anterior to them. As is well known, the brain in the 

 reptilia does not fill the brain cavity, bvit is supported by a mass of connective tissue 

 carrying lymph and fat masses ; so a cast of the brain cavity does not give an exact 

 copy of the brain. However, many points can be brought out by such a cast. 



" If the cast be held with the short terminal portion of the medulla horizontal, 

 the lower surface pitches downward at a sharp angle to a point anterior to the 

 tympanic region, and then ascends as sharply to the point of origin of the hypophysis. 

 The superior surface is horizontal and arched from side to side to a point over the 

 tympanic cavity and there tvirns upward at an angle of 45°. The angle thus produced 

 is marked b}' a low, narrow ridge running across the cast and marking the position 

 on the brain of a narrow and elevated cerebellum, Fig. 1 Cb., such as occurs in 

 Sphcnodon. This region was probably the seat of a large amount of connective tissue, 

 and it is probable that the upper surface of the medulla descended at as sharp an angle 

 as the lower. This would make still more marked the resemblance to Sphcnodon and 

 to the cast figured by Cope. This sharp bend of the medulla downward is not found 

 in other forms, though in the brain of Chelonia and some lacertilia a bend is apparent. 



"The sides of the medulla show most posteriorly the beginning of the twelfth 

 nerves. Figs. 1 and 2 (12), anterior to these the cast of the jugular foramen, Figs. 1 and 

 2 Ju., and finally the large casts of the tympanic cavity, Figs. 1 and 2 Ty. 



"Anterior to the tympanic casts a sharp constriction marks the ridge defining the 

 limits of the tympanic cavity, and then a sharp outswelling the point of exit of the 

 trigeminus nerve, Figs. 1 and 2 (5). Near where these leave the body of the cast a 

 small stub on each side marks the origin of the seventh pair. Figs. 1 and 2 (7). 



" The hypophysis is the most interesting feature of the brain. Descending between 

 the anterior inferior process of the petrosal and turning posteriorly, it occupies a small 

 notch in the posterior edge of the upper surface of the basisphenoid and then passes 

 directly into the body of the basioccipital throiagh the foramen mentioned. In the 

 Orocodilio a somewhat similar condition exists." 



Some additional points have been made out from specimens 1001 and 1002. The 

 distal ends of the opisthotics rest on or close to the upper edges of the quadrates and 

 are overlapped by the squamosals. On the left side of the cranial region of specimen 

 1002 the median portion of the stapes is preserved; it shows that the stapes was a 

 slender rod extending from the foramen to the quadrate just beneath the opisthotic, 

 unfortunately neither end is preserved. Cope speaks of both a columella auris and a 

 stapes but there is no evidence of more than a single bone in these specimens. The 

 semicircular canals of both sides are fairly well preserved and show the presence of a 



