68 FRANK BLAIR HANSON 



continuous with the epicoracoids. The ossification in each is 

 at exactly the same stage; the amount of soft cartilage around 

 the edges is the same in coracoid and sternum. At the anterior 

 end is differentiated a small region that corresponds to the 

 larger omosternum in the frog. We shall come back to Pipa 

 when treating some of the reptiles, and by a comparison attempt 

 to show that this subreptilian creature has a sternum essentially 

 like certain reptiles. 



Does Bufo (fig. 21) have a sternum? Kingsley ('17) would 

 say that since no ribs are in this region, no one can say. On 

 the theory of Ruge, this would be true, but if we compare the 

 sternum of Bufo with that of Pipa and the early stages in the 

 frog, it is hard to believe that there is any essential difference 

 between the two structures, although the connection of the 

 sternum with the epicoracoids in Bufo is not so extensive as in 

 many other Amphibia. The entire body of evidence in this 

 paper and many others on the shoulder-girdle in the Amphibia 

 can only lead to the conclusion that Bufo does have a sternum 

 and that it can only be derived from the coracoidal portions of 

 the shoulder-girdle. 



Siredon (fig. 22) has large coracoids and a considerable over- 

 lapping of their epicoracoidal edges. The interesting feature to 

 us is that the sternum lying immediately behind the overlapping 

 epicoracoids also shows very distinctly two grooves correspond- 

 ing exactly to those made by the overlying edges of the epi- 

 coracoids. It is the condition precisely to be expected of the 

 sternum if it were in an early stage a posterior continuous ex- 

 tension of the cartilage, sharing in the overlapping, and then later 

 had been cut off by sutures from the main element, but retaining 

 these evidences of its formation from the two epicoracoids. 



Little need be said concerning such a girdle as that of Dacty- 

 lethra (fig. 23) . There is no overlapping of the coracoids and no 

 sutural evidence in the sternum of the union of the two sides; 

 however, as this is an adult specimen, none need be expected. 

 Nevertheless, the intimate relation of sternum and girdle is 

 evident. 



In Calamites (fig. 24) we see a sternum that for the first time 



