The Columella Auris in Amphibia. 603 



end of the squamosum joined to the quadrate. From a morphological 

 viewpoint, however, it is not a matter of indifferent significance. 

 The connection of the columella with the squamosum and its forma- 

 tive cells is a primary one, while the direct articulation or junction 

 with the palatoquadrate is only secondarily established. The sig- 

 nificance of the relation becomes more impressive when the develop- 

 ment of the columella is considered. In the forms in which the 

 early development has been traced, — jSFecturus, Ambystoma, Crypto- 

 branchus, Spolerpes, Plethodon, — before cartilage has appeared in the 

 columella, when the squamosum is but a delicate scale of bone, a cord 

 of cells proceeds from the proton of the columella to the cells under- 

 lying the forming bone. The developmental relations will be considered 

 again in connection with the question of hyomandibular homology. 



Columella and Operculum. A second complication exists in 

 Amphibia due to the existence of two structures that are found fitting 

 into the fenestra vestibuli, and the failure to recognize this fact has 

 added another source of confusion in the elucidation of the relations 

 in this group. It is the first of these two elements, distinguished by 

 us as Columella, which possesses a suspensorial connection. The sec- 

 ond, termed by us the Operculum, possesses no such relation. In its 

 typical form as it exists in the adult Ambystoma, Diemictylus or 

 Salamandra, the operculum is a spheroid filling in the definitive 

 fenestra with whose lips it is connected by membrane only or pos- 

 sesses a slight cartilaginous connection at its caudal end. It may 

 be massive (spheroidal) as in Salamandra, or more plate-like as in 

 Triton. The cephalic end is included by the lip of the fenestra ; 

 the caudal end projects freely, covers the recessus perilymphaticus 

 externally and affords attachment to the M. opercularis. In the 

 families of the Plethodontidse and Desmognathidse the condition is 

 characteristic and unique ; the oval window has fitted into it a plate 

 whose cephalic portion possesses a well developed stilus and whose 

 caudal portion, offers attachment to the M. opercularis and covers 

 externally a recessus perilymphaticus; it seems therefore to repre- 

 sent both columella and operculum. 



The statement of Gaupp ('05) in reviewing the Amphibian sound- 

 transmitting apparatus (p. G05), that only by a stretch of the 



