The Columella Auris in Amphibia. 595 



it has in the adult, and the columella has no connection with the 

 palatoquadrate, os pterygoideum or os quadratum. Furthermore, 

 it is to be noted that it articulates with the lower edge of the squa- 

 mosum and not with its under surface. 



The newly hatched Cryptobranchus is of interest in this connec- 

 tion for two reasons: (a) the columella is represented by a con- 

 densation of cells from which a cord of cells passes cephalad (PL 

 VII, rigs. 52-53) and dorsad to the group of cells in whose midst 

 the squamosum is just appearing as a homogeneous scale of bone; 

 (b) the columella at this stage is pre-cartilage and is distinctly form- 

 ing outside the ear capsule. The chondrocranium is cartilaginous, 

 the fenestra clearly demarcated, and the precartilaginous columella 

 external to the membrana fenestras (Fig. 52). The development at 

 this stage closely parallels that of JSTecturus, as already described 

 (p. 590). It seems to us safe, therefore, to add Cryptobranchus to 

 ITecturus and Ambystoma as a form showing the extra-otic appear- 

 ance of the columella, and its early connection with the squamosum. 

 It is likewise noteworthy that the columella in all the larvae exam- 

 ined shows no cartilaginous connection with the otic capsule ; and 

 in the adult the fusion is very slender, — if indeed it exists. The 

 source of the cells that form the columella could not be determined 

 from the material at hand, although two embryos were examined. 

 Neither operculum nor opercular muscle are developed. 



It is interesting to note in concluding that Cryptobranchus is the 

 only form in which there has been general agreement as to the con- 

 nection of stilus with squamosum ; not so, however, the relation to 

 the facial nerve. Both Wiedersheim ('77) and Parker ('82b) 

 described the relation correctly and subsequently altered their state- 

 ments. 



Megalohatrachus. From the description of Parker ('82b), 

 Wiedersheim ('77), Osawa ('99), as from the dissection of a single 

 specimen in connection with this study, suffice it to state that it 

 shows essentially the same relations as Cryptobranchus. Osawa 

 (as quoted) describes the stilus as joining the palatoquadrate. 

 Parker states that the hyo-suspensorial cartilage (his epihyal) articu- 

 lates with the palatoquadrate ; in Cryptobranchus there is continuity. 



