354 H. D. REED 



FAMILY NECTURIDAE 



The sound-transmitting apparatus has been discussed at suf- 

 ficient length in another communication (Reed, '15); therefore, 

 only a summary is given as an aid to comparisons made later 

 in this paper. The columella appears in the usual fashion out- 

 side the ear capsule and the proton comes to lie for a short dis- 

 tance along the f enestral membrane. As chondrification advances, 

 the tip of the stlyus spreads over the fenestral membrane, but 

 to a very limited extent as compared with Amblystoma. Ap- 

 proximately a third of the plate, located in the cephalic part of 

 the fenestra, is formed in this manner. This area is triangular 

 in outline, the base being applied to the cephalic lips of the fen- 

 estra while the apex is on a level with, and extends slightly be- 

 yond the stylus. Other parts of the plate are formed by carti- 

 lage, produced within the membrane itself, and during growth 

 it becomes joined to that proliferating from the stylus (fig. 33). 

 The freedom of the definitive plate from the lips of the fenestra 

 and its formation partly from extraotic and partly from otic 

 tissues stamp it very decidedly as an intermediate in comparison 

 with the amblystomid and plethodontid types. 



FAMILY TYPHLOMOLGIDAE 



The general estate of the sound-transmitting apparatus in 

 Typhlomolge has been described by Kingsbury and Reed. The 

 serial sections of the specimen 95 mm. long have been carefully 

 reexamined in the light of what has been gained through develop- 

 mental studies of other species. The presence of an isthmus fen- 

 estralis indicates that the fenestral plate is of the plethodontid 

 type. In connection with this, as the best available evidence, 

 certain features are mentioned here for whatever value they may 

 have in a significant way. These features could not be depended 

 upon were it not for the consistent role of the isthmus in all 

 cases where it has been possible to trace its development. The 

 isthmus, projecting into the fenestral membrane, very soon ex- 

 tends underneath a bony plate to which it becomes attached 

 through cartilage cells, as shown in figure 17. The cartilage of 



