204 



REPTILIA. 



the ischium, expanded at its proximal end for union with the latter, and 

 showing the usual perforation. No dermal armour has been observed. 

 The length of the typical skeleton of Brontosaurus excelsus from the Upper 

 Jurassic of Wyoming, is not less than 17 metres. 



Diplodocus (figs. 123, 124). This genus has an elevated, laterally 

 compressed skull, with a relatively long and downwardly curved facial 

 region, and the feeble slender teeth confined to the anterior end of the 

 jaws (fig. 123 A). The external narial opening is very large, single, and 



FIG. 124. 



Diplodocus longus; transverse section of maxilla showing functional tooth 

 (fourth) in position and five successional teeth (2 6) in dental cavity, one- 

 half nat. size. Jurassic; Colorado, a, outer wall; b, inner wall; c, cavity; 

 /, foramen. (After Marsh.) 



placed at the apex of the skull, while the nasal bones are excessively 

 shortened as in the Cetacean mammals. In advance of the usual ant- 

 orbital vacuity, there is another comparatively small vacuity in the 

 maxilla. In the type specimen there is also an irregular vacuity (perhaps 

 accidental) in the parietal region. The orbit is large and laterally placed ; 

 the supratemporal vacuities are very small ; and the mandibular suspen- 

 sorium is much inclined forwards. The palate (fig. 123 B) is remarkable 



