326 H. D. REED 



the columella. Comparisons were also made with the sound- 

 transmitting apparatus of the Salientia. 



There remain to be considered certain points that are con- 

 cerned with the morphology of the fenestral elements within the 

 various groups of the tailed amphibia themselves and the zo- 

 ological significance of these structures. The Amblystomidae and 

 Salamandra possess the two elements mentioned above. This is 

 the most generalized state found among the terrestrial species. 

 All other salamanders in the adult state possess only a single ele- 

 ment filling the foramen vestibuli. Such forms are: Crypto- 

 branchidae, Proteidae, Plethodontidae, Desmognathidae, Am- 

 phiumidae, Sirenidae, and Triton and Diemictylus. These 

 groups include the majority of all living species. In certain of 

 these forms the morphology of the sing^le fenestral plate was 

 demonstrated in the papers already mentioned. In Triton and 

 Diemictylus the single element possesses only the characteristics 

 of the amblystomid operculum; that is, it is without stylus and 

 suspensorial connections, but possesses a perilymphatic promi- 

 nence, between which and the supraclavicle the M. opercularis 

 extends. Development showed that the single element in Die- 

 mictylus and Triton is the operculum or that which corresponds 

 to the caudal of the two elements in the Amblystomidae and 

 Salamandra. It further showed that the columella is present, 

 but disappears as such at an early period through complete 

 fusion with the cephalic lips of the fenestra (fig. 21). In a similar 

 manner it was revealed that the single element of the Crypto- 

 branchidae represents the columella of the amblystomid forms, 

 it being wholly of extraotic origin and possessing only the sus- 

 pensorial connections. 



With regard to the other forms, however, definite information 

 was not forthcoming at that time to account for the presence of a 

 single element in the fenestra. In the Plethodontidae and Des- 

 mognathidae, for example, the single fenestral element possesses 

 at one and the same time the connections and relations of both 

 columella and operculum (fig. 22). Through a stylus and liga- 

 ment the cephalic end of the plate is connected with the suspen- 

 sorium, and in its caudal portion there is a well-defined peri- 



