PROTOROSA URIA 1 3 7 



in a serpentine way, for it could not have progressed very rapidly 

 by the aid of its legs alone. The hind legs are longer than the 

 front legs, and they were connected firmly with the body by means 

 of a sacrum. The number of vertebrae in the neck is only five. 

 The number of dorsal vertebrae is forty-three, a larger number 

 than is known in any other air-breathing vertebrate with legs. 



Upon the whole, these lizard-like, almost snake-Hke pleuro- 

 saurians present some very curious adaptations to water life. In 

 water they were doubtless speedy, swimming in serpentine undula- 

 tions, with the small legs for the most part folded against the body 

 and only of occasional use. Doubtless, too, had the pleurosaurs 

 lived longer in geological history, they would have become quite 

 snake- or eel-hke, just as have some modern salamanders. 



In all probability the pleurosaurs lived habitually in fresh water, 

 perhaps visiting the shores for refuge, or for the hatching of their 

 young. That they were not on the way toward a terrestrial 

 snake-Uke body is evident from the flattened tail, and especially, 

 the crest of scales above; the tail was like that of the sea-snakes 

 of the present time. Pleurosaurus, then, affords the solitary 

 instance among reptiles of aquatic adaptation by the diminution 

 of both front and hind extremities and the acquisition of a snake-, 

 like body and snake-like habits. 



