CROCODILIA 213 



matrix in such a way as to indicate a slender thorax and 

 abdomen, not the broad body of the modern crocodiles. The 

 abdominal ribs, that is, those protecting the region on the 

 under side of the body between the breast bone and the pelvis, 

 are strongly developed in Gcosaurus. The sternum, always present 

 in other crocodiles, is wanting in Gcosaurus. 'J'he shoulder- 

 blades and coracoids, often changed in shape in water reptiles, 

 are not unlike those of the amphibious crocodiles, but are smaller 

 and flatter. 



The fore limbs, to use Professor Fraas's words, "are among the 

 most interesting of all the peculiarities of Gcosaurus,''^ and show very 

 clearly that these animals were excellent swimmers. The humerus 

 is remarkably short and broad; the two bones of the forearm, the 

 radius and ulna, are broad, rounded, or angular plates, not long 

 bones, as in other crocodiles; the wrist bones also are broad and 

 plate-like. The three bones of the thumb, that is of the digit which 

 received most strongly the impact of the water in swimming, are 

 also broad and flat. All of these bones are marvelously aquatic in 

 type, as will be evident from a comparison of them with the cor- 

 responding bones of the ichthyosaurs and mosasaurs. The bones 

 of the other fingers, however, were not much changed from the 

 ordinary crocodilian form, as a further comparison of them with the 

 fingers of a land crocodile will show. Furthermore the whole limb 

 or paddle was very small in comparison with the hind leg, and it was 

 attached very near to the head. The relative proportions of the 

 front and hind limbs in the geosaurs, gavials, and alligators are 

 instructive as showing the progressive decrease in size of the front 

 legs from the subaquatic, through the semiaquatic, to the almost 

 purely aquatic type. The hind legs, strangely enough, were not 

 very dift'erent in size and structure from those of the gavials or teleo- 

 saurs. The thigh bone is long and slender, though the bones of the 

 leg and ankle are somewhat shortened and flattened, as are also 

 those of the first toe. There were no claws on the hind feet, a 

 distinctly aquatic adaptation, and the toes were certainly webbed. 

 The pelvis, while not especially stout, is of good size, and was firmly 

 attached to the sacrum. 



