The Columella Auris in Ampiiibia. 



610 



of high frequency are not detected if transmitted to the animal 

 through a dense medium. Experimentation along this line may 

 prove very interesting and valuable. 



During the larval period, and in aquatic or partly aquatic forms 

 during adult life, the connection of the fenestral plate is with the 

 suspensorium. Thus it would appear that jars or vibrations are 

 transmitted from the objects, upon which they are resting, to the 

 floor of the mouth, after which the course is through the suspen- 

 sorium to the columella and thence to the inner ear, as has been 



StC, 



M. L 



H. a. 



Fig. 21a. Schema to illustrate the possible method of communication be- 

 tween the inner ear and the exterior for larvae and thoroughly aquatic adult 

 forms. Col., Columella ; F.v., fenestra vestibuli ; H.a., hyoid arch ; L.s-c, liga- 

 mentum squamoso-columellare ; M.I., skeleton of the lower jaw; Pg., paloto- 

 quadratum ; 8p., os squamosum ; St.C, stilus columellse. 



suggested by Gaupp ('05, '07). The possibility of such a functional 

 mechanism is illustrated in Fig. 21a. 



At transformation when terrestrial life is assumed, in certain 

 forms, a different type of communication with the exterior is formed. 

 The columella becomes fused with the ear capsule while a free plate, 

 the operculum, is formed behind and below as in Ambystoma or 

 the caudal portion of the fenestral plate remains free as in the 

 Plethodontidse and some others. This plate is placed in communi- 

 cation with the exterior by the M. opercularis, connecting it with 

 the shoulder girdle. Thus jars and vibrations may be transmitted 

 through the arm to the M. opercularis, thence to the operculum and 

 finally to the inner ear, as shown in Fig. 21 6. 



