The Columella Auris in Amphibia. 615 



namely, that of distinguishing cells of extra-otic origin from the 

 periotic blastema. It has, in fact, been so far impossible in Am- 

 bystoma and Spelerpes to determine whether or not the fenestral 

 plate of the columella embodied a periotic element. It may be said, 

 however, that in its chondrification and growth the stilus is an integral 

 part of the columella as a whole and not an element from outside 

 secondarily fused with the plate, — representing, therefore, a structure 

 which could by itself be homologized with the hyomandibulare, as 

 was done by Parker. 



The articulation of the stilus columellse with the palatoquadrate, 

 which had been mentioned, as quoted above, by Gaupp (cf. Wieder- 

 sheim '06, Gaupp '05) as the significant relation for the hyomandib- 

 ular homology, has been shown to be a connection secondarily estab- 

 lished during groM'th and development apparently due to a shifting 

 of the connection from the. squamosum to the palatoquadrate, in 

 many forms a longer or shorter process of that cartilage developing 

 with which it is articulated or fused. If this connection is in the 

 nature of a secondary adaptation, — and this interpretation is the 

 more probable, — its phylogenetic significance becomes doubtful. 

 There is, however, an association of the two structures of a primary 

 ontogenetic character and suggestive of profound significance. It 

 is to be recalled that in those forms in which the early development 

 of the columella has been traced, the cell mass constituting the proton 

 of the columella is directly connected with the cells between squa- 

 mosum, the otic process of the palatoquadrate and the otic capsule 

 external to the lateral semicircular canal. If a connection with the 

 palatoquadrate is to be considered of value in determining the hyo- 

 mandibular homology, it would seem to us, therefore, to be expected 

 that in the displacement of the hyomandibulare from the suspen- 

 sorium, it would be that portion of the upper end of the palatoqua- 

 drate which comes to articulate with the otic capsule with which the 

 homolog of the hyomandibulare would be joined rather than a point 

 farther down. If, on the other hand, as maintained by Fuchs, the 

 ancestry of the Amphibia is to be sought far back among the primi- 

 tive elasmobranchs, it is in this region, — over the lateral semicircular 

 canal caudad of the otic articulation of the palatoquadrate, — that the 

 connection of its vestigium might be sought. 



