The Columella Auris in Amphibia. 621 



by the limbs, thereby raising the floor of the mouth above the ground. 

 Thus communication of the internal ear with the exterior through 

 the suspensorium and floor of the "mouth is lost. By the detachment 

 of a portion of the M. intertransversarius capitis inferior which 

 becomes the M. opecularis, the operculum is connected with the 

 shoulder girdle and communication of the inner ear with the 

 exterior is again established, — through the arm and shoulder girdle. 



Summary. 



While to a certain extent (hyomandibular homology) comparison 

 has been made with fishes, comparisons between the amphibian audi- 

 tory apparatus and those of reptiles and mammals have not been 

 attempted. The terms "stapes" and "stapedial" have been purposely 

 avoided since it has seemed to us by no means conclusively shown 

 that the amphibian columella is simply the homolog of the first seg- 

 ment of the mammalian chain of bones. Although we have fully 

 appreciated that this investigation is but a part of the larger problem 

 as was indicated at the beginning of the paper, the main aim has 

 been the determination of facts for a large number of tailed am- 

 phibians, realizing that weaknesses in broad generalizations are 

 in most instances due to drawing conclusions from insufficient data; 

 for illustration of which it is unnecessary to go outside the limited 

 field of investigation covered by this paper. The amphibian group 

 presents within itself many problems of both local importance and 

 general bearing that require further investigation, and it was this 

 narrower field that particularly engaged our attention. Some of the 

 general aspects of the problem we hope to deal with subsequently. 



The main results were given in the first portion of the paper; 

 they are restated below in somewhat extended form. 



1. Several (4 to Y) different types of "columella auris" are found 

 in urodeles. 



2. There are two morphologically distinct fenestral structures 

 found in the group : Columella and Operculum. 



3. The Columella possesses a stilus, tends to fuse with the cephalic 

 portion of the fenestral margin, and in ontogeny seems to come from 

 outside the otic capsule. 



