208 VEBTEBRATA. 



In some of their characters the Dinosauria approach the 

 ostriches ; but their metatarsal bones were not anchylosed to the 

 tarsus, except partially in Compsognathus, which it is supposed must 

 have walked more or less in an erect position. Huxley considers 

 that the gradation between birds and reptiles will be found in this 

 group. 



These Saurians were mostly of gigantic size ; Cetiosaurus was 

 60 or 70 feet long ; Compsognathiis, however, was only about two 

 feet long. They are found chiefly in the Oolitic and Cretaceous 

 formations. 



*Cetiosaurus. *Megalosaurus. *Iguanodon. 



*0mosaurus. *Compsognathus. 



Order VIII. ANOMODONTLA. 



DlCYNODONTIA. 



No teeth, or with closely-set teeth in both jaws, or two large 

 tusks in the upper jaw. Vertebras amphicoelous. Sacrum large. 

 Limbs ambulatory. No exoskeleton. 



In Dicynodon an important step towards the mammalian type 

 is made in the constant renewal of the tusks from the matrix, as 

 in the long-lived and ever-growing tusks and scalpriforni incisors 

 of the Mammalia. In their beak, sheathed in horn, they resembled 

 the Chelonia. They are found in the Trias of South Africa, 

 Europe, and Bengal. 



*Oudenodon. *Dicynodon. 



*Rhynchosaurus. 



Order IX. CHELONIA. 

 TESTUDINATA. CATAPIIRACTA. 



No teeth. " Trunk-ribs broad, flat, suturally united, forming 

 with their vertebrae, sternum, and dorsal bones an expanded 

 thoracico-abdominal case." External nostril single. Eyelids. A 

 sacrum. 



The upper plate, or " carapace," is composed of the dorsal ver- 

 tebrae and ribs; the lower, or "plastron," represents the sternum. 

 These are formed of bony plates covered with unconformable 

 horny scales. The vertebras oi the neck and tail are alone movable. 

 The lungs extend into the abdominal cavity with the viscera ; and, 

 owing to the immobility of the ribs, these reptiles, like the Batra- 

 chia, swallow the air they breathe. 



