REPTILES. 3 1 5 



sibly in some theropoda. It consisted of separate ossicles or 

 bony plates, some of these upon the back of the stegosaurs 

 measuring a yard across. These forms also had large bony 

 spines on the tail as weapons of offence and defence. 



While as a rule the vertebrae were amphiccelous, occasionally 

 those of the neck were opisthoccele, the rest being flat. Rarely 

 proccelous vertebrae occurred in the tail. As a rule, there were 

 10 cervical, 18 trunk, 3 to 6 sacral, and 30 to 50 caudal verte- 

 brae. A double proatlas occurred in the neck, and occasionally 

 the number of sacrals exceeded 6, there being 10 in Polyonax. 

 The caudals frequently bore chevron bones, forked at their free 

 ends. The ribs are without uncinate processes, and abdominal 

 ribs occur only in theropoda. Usually, as in the crocodiles, 

 there is a preorbital fossa between the eyes and the nostrils ; 

 teeth occur only on the jaws. Clavicles and an episternum are 

 known only in Iguanodon. The scapula is large, the coracoid 

 small and discoid. The anterior limbs are frequently much 

 shorter than the posterior, and these forms must have had bi- 

 pedal or kangaroo-like habits. The feet are digitigrade or plan- 

 tigrade ; the metapodial bones are variously modified, and the 

 feet are pentadactyl, although in many but three toes were 

 functional. 



The brain cavity shows, according to Cope, that the brain 

 -vas exceedingly small, while the neural canal in the sacral region 

 was much larger than the brain cavity (ten times as large in 

 some stegosaurs), implying a great lumbar enlargement of the 

 cord. At least some of the order (Compsognathus) were vivi- 

 parous. The group is confined to mesozoic rocks, and attained 

 its greatest development in the upper cretaceous. 



SUB-ORDER i. SAUROPODA. 



Large Dinosaurs with the fore feet little shorter than the hind ; anterior 

 vertebrae opisthocrelous, the others amphiccelous or flat, the centra with 

 large lateral cavities. A large preorbital fossa, nares elongate ; premaxilla 

 toothed, teeth in alveoli, spatulate, the sharp margins smooth. No post 

 pubis; bones of the extremities massive, femur without inner trochanter, 

 all feet plantigrade, pentadactyl, digits clawed. This sub-order contained 

 the largest land animals known, most or all of them probably being herbiv- 

 orous. Amphicoelias (Brontosaurus), Camarasaurus (Atlantosaurus), and 



