The Columella Auris in Amphibia. 



589 



remain cartilaginous throughout the greater part of their extent, the 

 bonj portion of the plate being much thinner than the margin as 

 in the Plethodonticte. At its base the stilus is composed entirely of 

 bone (Fig. 17) which gradually l)eeomes a sheath surrounding a core 

 of cartilage. In the distal half (Fig. 16) the stilus is composed of 

 cartilage alone. 



Between the distal end of the ceratohyal and the otic region of the 

 skull is a wide sheet of fascia, the caudal portion of which is attached 

 to the stilus and in this region becomes a relatively strong ligament 

 between the columella and hyoid (PL X^ Fig. 68). 



Developmental stages have not -been studied, laut it appears that 

 in Typhlomolge the ty])e of sound-transmitting apparatus is essen- 

 tially that of the Plethodontida\ ' ' . 



^^^>- 



Fig. 17. Typhlomolge, adult. C.I., canalis lateralis ; Col., columella ; St.C. 

 stilus columella; 8q., os squamosimi. 



Necturus. 



Although the relations and development of the otic region of the 

 skull in Necturus have been already quite well worked out by several 

 persons, because of its historic interest in this connection and the 

 general acceptance of its low systematic rank, it has been included 

 for brief consideration. In illustration of the conditions in this 

 form four photographs are introduced. Figs. 57, 58, 59 (PI. VIII), 

 and 60 (PL IX). 



Miss Platt ('97), p. 430, described the early development in the 

 ear capsule in Xecturus. In a 19 mm. larva the "operculum" is 



