PROGANOSAURIA 131 



side of the body; its hind legs are used more as propellers, with 

 the knee flexed and the feet turned outward and expanded. The 

 legs of the proganosaurs doubtless were used in the same way, as 

 shown in the restoration, which has been modified from the original 

 of Dr. McGregor in accordance with this probable use of the leg^. 



There seems to be an incongruity between the posterior nostrils 

 and the heavy flat ribs, the former suggesting free swimming and 

 diving habits, the latter shallow-water and bottom habits. Possibly 

 the position of the nostrils has been the result of the great elonga- 

 tion of the face in front of the nostrils; and we know that their 

 posterior position in the phytosaurs (Figs. 95 and 96) has not been 

 due to swimming habits only. ^ 



Nothing has been discovered to indicate the nature of the 

 external covering of the body. Possibly, even probably, the skin 

 was more or less covered by horny scales or plates, though it may 

 have been quite bare, as in the salamanders. 



To which other reptiles the proganosaurs are nearest related 

 has long been a subject of dispute, and still is. The more 

 probable view, however, is that they were a very early branch of 

 the most primitive stock of reptiles, the Cotylosauria, one that 

 soon perished, leaving no descendants, unless possibly the ichthyo- 

 saurs were their progeny. Some writers have thought that they 

 were the early ancestral stock of the plesiosaurs, and they are often 

 classified with the Sauropterygia. Still others have believed that 

 they were an early side-branch of the great group of Rhynchoce- 

 phalia. And this doubt has been chiefly due to our imperfect knowl- 

 edge of the bones of the cranium. As has been explained, very 

 much stress in the classification of reptiles has been laid by students 

 on the possession of one, two, or no openings on the side of the 

 skuU back of the eyes. And this part of the skull of the Progano- 

 sauria has not yet been satisfactorily made out. Dr. McGregor 

 thought that there are two openings iri the temporal region, allying 

 the group with the Rhynchocephalia. Dr. Huene is morfe positive 

 that there is but one, like that of the ichthyosaurs. In this state 

 of indecision, the proganosaurs may be dignified by giving them an 

 ordinal position by themselves. 



