388 DINOSAURIA. PTEROSAURIA. 



region. The parietals and squamosals project back over the neck as a 

 shelf -like crest, the edge of which carries projections. There is a toothless 

 rostral bone in front of the premaxilia, and a predentary, also edentulous, 

 on the mandible. Small supra-temporal fossae are present, but no lateral - 

 temporal. All the bones are solid. The teeth with forked roots and 

 crushing crowns are borne by the maxilla and dentary. The fore -limbs are 

 a little shorter than the posterior and have five hoofed digits. The sacrum 

 is reinforced by adjacent lumbar and caudal vertebrae, and the ilium is 

 extended antero -posteriorly. The pubis is directed forwards and meets 

 its fellow ; there is no postpubis. The astragalus is fused with the tibia. 

 There are three hoofed toes. A dermal armour appears to have been pre- 

 sent. They are known from the Cretaceous of Europe (fragments) and 

 N. America. Triceratops Marsh (Fig. 214), skull 7 feet long, larger than 

 in any other known land animal ; body 20 feet. Upper Cretaceous of 

 Wyoming ; Rterrholophus Marsh. 



FIG. 214. Triceratops prorsus x ^ (after Marsh). 



Sub-class 5. PTEROSAURIA. 



With a superior and inferior temporal arcade, a fixed quadrate, and the- 

 codont dentition ; without pineal foramen. The fore-limbs are adapted for 

 flight and the bones are hollow. 



The Pterosauria, or Pterodactyls, as they are sometimes called, were 

 flying reptiles the remains of which are found in the Mesozoic rocks from 

 the Lower Lias to the Cretaceous. In their external appearance and habit 

 of life they present great resemblances to birds, but in the absence of 

 feathers and the structure of the skeleton they differ considerably from 

 these animals. They possess an elongated head which is set on the neck 

 at a right angle, a long neck composed of elongated vertebrae, a very 

 large anterior limb, the ulnar digit of which is enormously elongated to 

 form the support of a patagial expansion of the integument (Figs. 215, 

 216), and a keeled sternum. Moreover the bones are hollow, and casts 

 of the skull which have been obtained in one or two cases show that 

 the brain possessed a large cerebellum extending forwards to the well- 

 developed cerebral hemispheres and pushing apart the large optic lobes. 

 There is evidence also of flocculi on the cerebullum. 



The vertebral column is divided into cervical, dorsal, sacral and caudal 

 regions, with about seven, fifteen, three to five and ten to forty vertebrae 

 respectively. The precaudal vertebrae are procoelous the caudal amphi- 

 coelous. The cervical and anterior dorsal ribs are two-headed. The 



