110 BULLETIN OF THE ESSEX INSTITUTE. 



species described renders it difficult to make any accurate 

 statements in regard to these organs which shall apply to 

 the group as a whole. More extended study may show 

 the prevalence of a limited number of these types as is 

 suggested by the similarity between Amblystoma and 

 Plethodon. 



Quadrates, arising independently near the anterior end 

 of the otic capsules, later become attached to the rest of 

 the skull by three or four processes. The ascending 

 process unites it with the trabecular crest ; the palato- 

 basal with the parachordal ; the otic with the otic capsule ; 

 and the stapedial process, when present, unites it with the 

 stapes. The palato-basal and otic processes become so 

 intimately related that the blood vessel running between 

 them is the only line of demarcation. A pterygoid process 

 running forward from the body of the quadrate may or 

 may not be present. When present it ends freely in front, 

 not coming in contact with the anterior end of the trabec- 

 ula and nasal capsule as occurs regularly in the Anura. 

 Ranodon forms the only known exception among the Uro- 

 deles to this last statement. 



PlPA AMERICANA (FlgS. 20-21). 



In the single stage of the chondrocranium of Pipa 

 which I have modelled, ossification has proceeded so far 

 that many of the cartilages appear only as remnants of 

 what they were earlier. A brief outline of this skull, 

 however, may serve as a basis from which, with the aid of 

 other studies upon the Anura, especially Gaupp's exhaus- 

 tive work upon Rana fusca, we may contrast the chondro- 

 cranium of this group with that of the Urodela. 



The occipital processes have fused with the otic cap- 

 sules and their distal ends have developed into the synotic 



