CHAPTER X 



DIXOSAURIA CROCODILIA 



SUB-CLASS V.DINOSAURIA. 



Mesozoic, long-tailed, toothed reptiles, with distal ischiadic sym- 

 physis, terrestrial limbs, large fixed quadrate bones and 

 bifurcated ribs. 



THE Dinosaurs begin and end with the Mesozoic epoch, and 

 have a world-wide distribution. The name, " terrible Eeptiles/' 

 refers to the gigantic proportions which many of them attained, 

 not a few of them surpassing in size and shape the fantastic 

 pictures of the dragons of our fables. Although these creatures 

 came to an end millions of years before the first man-like beings 

 appeared, it is reasonable to suppose that the widely-spread myths 

 of dragons are based upon the accidentally disclosed skeletons of 

 these monsters. 



The skull is built after a plan which may be derived 

 from a combination of the Crocodilian and Ehynchocephalian 

 skulls, but the detail varies considerably in the many and 

 much diversified members of this large sub-class. There is 

 as a rule a pre-orbital foramen, which is smallest in the Orni- 

 thopoda. The orbit is completely encircled by bones, and 

 the temporal fossa is divided by a squamoso-postfrontal or 

 post-orbital bridge into a smaller supra-, and a much wider 

 infra-temporal portion, the latter being bordered below by the 

 jugal and quadrat o-jugal, and this is firmly connected with the 

 quadrate by an ascending process. The quadrate is long, more 

 or less vertical in position, slanting either forwards or backwards, 

 and firmly fixed above by the squamosal, perhaps also by a supra- 

 temporal bone. The orbit is bordered by the jugal, lacrymal, 

 pre- and post-frontals. The interparietal foramen seems to be 



