196 REITILIA. 



ORDER 7. DINOSAURIA. 



During the Triassic period a race of land-reptiles arose, at 

 first so generalized that it is difficult to separate them from the 

 Rhynchocephalia and Crocodilia, but afterwards constituting at 

 least one distinct order. These are the so-called DINOSAURIA 

 (also named PACHYPODA and ORNITHOSCELIDA), which became 

 dominant during the Jurassic and Cretaceous periods, in the 

 interval between the decline of the Anomodonts and the 

 dominance of the Mammalia. Their remains have been dis- 

 covered in Europe, Syria, India, South Africa, Madagascar, 

 North Australia, South America, and North America. 



All the Dinosaurs possess limbs adapted for habitual sup- 

 port of the body on land, and some exhibit hind quarters so 

 disproportionately massive that there is not much doubt these 

 walked ordinarily on their hind limbs. The form and great 

 size of the tail, however, suggest that they were amphibious in 

 habit, the caudal appendage being admirably adapted for 

 swimming. Some are very massive, others with delicate and 

 hollow bones ; the teeth of some show that they were car- 

 nivorous, while those of others prove with equal certainty that 

 they were herbivorous. 



In the skull the investing bones of the temporal region 

 contract into an upper and a lower temporal arcade, and the 

 large quadrate is firmly fixed. A pineal foramen has not 

 been clearly observed. There are no teeth on the palate. The 

 cervical and thoracic ribs are distinctly double-headed, and the 

 neural arches bearing the latter are much raised for the 

 enlargement of the thoracic cavity. The sacral vertebraB, two 

 or more in number, are fused together. The chevron bones of 

 the tail are articulated intervertebrally. The pectoral arch is 

 imperfectly known, but clavicles seem to be absent, while a 

 pair of problematical ossifications sometimes found, appear to 

 be referable to the sternum. All three elements of the pelvis 

 enter the acetabulum, and the ilium is extended antero- 

 posteriorly. The tibia exhibits a large cnemial crest, the fibula 

 is complete, and the proximal tarsals are only two in number, 

 an astragalus and a calcaneum. The astragalus sometimes 



