No. 498] 



THE CAUDATE AMPHIBIA 



30.5 



latter group is characterized by the long curved ribs 

 borne intercentrally. There seem to be some difficulties 

 in this classification, but it is hoped that they may be 

 cleared up by future investigation. 



The Branchiosauria, as has been several times sug- 

 gested by various authors, represent the ancestral forms 

 of at least the tailed division of the Amphibia. A sug- 

 gestion as to the ancestry of the tailless forms will be 

 given elsewhere. The conclusion that the Branchi- 

 osauria are the direct ancestral forms to the modern 

 Caudata is based on several characters. These char- 

 acters are: the structure of the skull, the structure and 

 form of the vertebrae and ribs, the number of digits, the 

 arrangement of the phalangeal elements, the characters 

 of the pectoral and pelvic girdles, the character of the 

 lateral line system, the structure and form of the long 

 bones and finally the shape of the body ; all of which will 

 be discussed below. 



It has been suggested on embryological grounds that 

 the Amphibia are a degenerate group (3) and this is 

 borne out, in so far as the Caudata are concerned, by a 

 study of the cranium of the early and recent forms as 

 well as by other structures. The cranium of the Branchi- 

 osauria is almost identical in structure with that of the 

 Microsauria and it exhibits a completely roofed-over skull 

 with only five openings, namely, those for the orbits, the 

 nostrils and the pineal opening. 



The elements forming the roof of the skull are quite 

 constant in the Branchiosauria and also in the Micro- 

 sauria and they differ only in position and relations. 

 Practically the same elements form the skull roof in the 

 two groups, but the forms differ in other important re- 

 spects. In the skull of the Branchiosauria we find in the 



entire length of the skull. These are (beginning an- 

 teriorly) : the premaxiltes, the nasals, the f rentals, the 



elements lie others which va 

 extent ; the median elements ; 



