RANK OF NECTURUS AMONG TAILED BATRACHIA. 69 



The first five bones mentioned in the above table need no com- 

 ment since they are universally present. Of the other " roof 

 bones " of the Urodele skull, the nasals and prefrontals which 

 are present in the gill-less adults, are completely lacking in Nec- 

 tunts and in the larval Spelerpes, and seem to be absent in the 

 larvse of other forms (as e. g., Dieinyctylus, Parker, 82$, p. 178), 

 or but slightly developed (Salainandra, Parker, 82^). Quite 

 characteristic is the occurrence in the larvae of Urodela of a Ptery- 

 go-palatine (or palato-pterygoid) extending from the ventral side 

 of the quadrate cartilage to the roof of the mouth where as the 

 palatine portion, it is typically tooth-bearing. In the adult gill- 

 less forms, the palatine portion becomes separated from the ptery- 

 goid portion and fused with the vomer forming a new osseous 

 skeletal unit, the Vomero-palatine. The Pterygoid portion may 

 be absorbed completely, or remain as a distinct bone, the 

 Pterygoid. 



The Maxillare is lacking in the larval forms or if present, as it 

 seems to be in advanced Amblystoma larvae and the Axolotl, it is 

 but weakly developed. In all gill-less adult Urodela it is present. 



The quadrate in Ncctnrus is peculiar. The lower end, which 

 articulates with the mandible is ossified, while the body of the 

 Quadrate and the otic, trabecular and basilar processes remain 

 cartilaginous. Ossification first appears in a bone, which I call 

 here bone " X " ! upon the upper (dorsal) surface of the quadrate 

 cartilage, slightly before hatching. It appears to be at first 

 entirely distinct from the cartilage. The lower end soon becomes 

 closely applied to the quadrate cartilage and finally fused with it. 

 From this (as a center ?) a zone of ossification spreads inside and 

 outside around the lower end of the cartilage, forming a ring of 

 bone. It was interesting to find in the larval Spelerpes a precisely 

 similar method of ossification, identical, it seemed, in all respects 

 with that in Necturns, save that the primary ossification was more 

 closely associated with the cartilage. In the larva, the ossifica- 

 tion does not proceed beyond the stage found in Ncctnrus. The 

 bone "x" coossifies at its distal end with the lower end of the 

 quadrate, but proximally is free from it. In the adult Spelerpes, 



1 Cf. Kingsbury, B. F. " Columella Auris and Nervus Facialis in the Urodela," 

 Joiu-n. Comp. Neural., Vol. XIII., No. 4, 1903. 



