DINOSAURIA 



CHAP. 



Allosaurus, from the Upper Jurassic of North America, with 

 only three toes. Ischia and pubes united into one symphysis. 

 Anterior extremities very short. Sacrum consisting of four 

 vertebrae. Total length of some of the larger species about 

 twenty feet. 



Cm-atosauTUS nasicornis, from the Upper Jurassic of Colorado, 

 is about seventeen feet long. The generic and specific names 

 refer to the nasal bones, which are raised into an unpaired 



Fig. 99.— Skeleton (xjij) and skull of Geratosaurus nasicornis. (After Marsh.) a, 

 Nasal cavity ; b, bony horn-supporting excrescence ; c, pre-orbital fossa ; d, orbital 

 fossa. 



longitudinal crest. This, by its rough surface, suggests that it 

 was covered by a horny sheath, or carried a horn. The large 

 skull, about two feet in length, is armed with strong, slightly 

 curved, laterally compressed, sharp teeth, unequal in size. The 

 pre-orbital foramen is large, bordered above by the prefrontals, 

 which are raised into prominent knobs. The supratemporal 

 foramina are extremely small, the lateral foramina very large. 

 The quadrate slants backwards. The sacrum consists of five 

 vertebrae. The caudal vertebrae carry long and slender chevron- 

 bones. The pubes and ischia are long and slender, each forming 

 a separate symphysis at their broadened ends. The three meta- 



