REPTILES. 329 



ORDER IX. PTERODACTYLIA (PTEROSAURIA, 

 ORNITHOSAURIA). 



Extinct reptiles adapted for flight. Skin naked, bones of 

 limbs and vertebrae hollow ; the caudal vertebrae amphiccelous, 

 the others procoelous ; three to five vertebrae fused to form a 

 sacrum. Skull bird-like in shape and in obliteration of sutures ; 

 supra- and infratemporal and preorbital fossae present ; a bony- 

 sclerotic ring ; premaxilla large ; teeth, when present, in alveoli ;: 

 quadrate immovable. Ribs two headed, sternal and abdominal 

 rib present ; sternum keeled ; episternum and clavicles absent. 

 The fore limbs have the fifth digit greatly elongate, supporting 

 a membranous wing extending from the side of the body as in 



FIG. 322. Restoration of Dimorphodon, after Woodward. 



the bats. The other digits are normal, except the first, which is 

 vestigial or absent. The pelvis is weak, the hind limbs reduced, 

 the feet five-toed. The tail may be long or short. 



The pterodactyls were confined to the Jurassic and creta- 

 ceous periods of Europe and North America. In habits they 

 were bird-like or bat-like. Some of them were sparrow-like im 

 size, while in others (Pteranodon) the skull was three feet in 

 length, and the wings had an expanse of twenty feet. Casts of 

 the brain cavity show that the brain was more like that of birds- 

 than of other reptiles, especially in the shortness of the hemi- 



