SOUND-TRANSMITTING APPARATUS OF CAUDATA 363 



have been extended and pronounced, for the columellar element, 

 which is useless on land, has disappeared \Yithout leaving a trace 

 in the adult. On the other hand, there are structural features 

 which argue that this secondary aquatic period has been long 

 enough to admit of certain readjustments of the sound-trans- 

 mitting apparatus to this type of abode. Extending between the 

 operculum and the hyoid is the extremely dense and large liga- 

 mentum hyo-operculare which places the inner ear in commu- 

 nication with the exterior as perfectly as could the columella 

 itself. This ligament is by far the largest and most pronounced 

 of any ligament in this region in any urodele. Although it is 

 attached to the operculum, and is given a name which indicates 

 its relations, it is quite likely that it represents the ligamentum 

 hyocolumellare of other urodeles. The extent and relations of 

 the general sheet of fascia in which it is formed admits of no 

 other conclusion. Siren is the only urodele in which the oper- 

 culum has such relations with the hyoid. The only interpretation 

 of its relations here seems to be that of compensating the loss of 

 the columella in transmitting disturbances from the surrounding 

 water to the inner ear. 



It seems probable that the morphology of the sound-trans- 

 mitting apparatus in the Tritons and Sirens and their past history 

 are identical; but this does not necessarily argue for a close re- 

 lationship of these forms within the legion itseK. Norris ('13), 

 in his work upon the cranial nerves of Siren, refers to strong sim- 

 ilarities between it and other urodeles, which is significant in 

 the present consideration in two connections : one bears evidence 

 in support of the view that Siren is not a primitive form, while 

 the other points to a close relationship with those urodeles which 

 comprise legion I as here constituted. Bearing upon this point 

 in particular, in his summary Norris writes: "The contribution 

 of maxillaris and buccalis fibers to the profundus palatine anasto- 

 mosis has such a closely corresponding arrangement in Triton 

 (Coghill) and also in Salamandra, if von Plessen and Rabino- 

 vicz's figures be correct, that it can hardly be explained as inci- 

 dental." 



