556 B. F. Kingsbury and II. D. Heed. 



mosum, otic capsule and otic process of the palatoquadrate. The 

 stilus appears to chondrify out into this tissue, the unchondritied 

 portion of which becomes the Lig. squanioso-columellare. 



The development as given above agrees completely with the con- 

 cise description of Killian ('90) for the development in Siredon. 

 He terms the columella Operculum and had no knowledge of the 

 interesting changes occurring at transformation. 



During the period of larval growth the portion of the columella 

 fitting into the membrane increases greatly in size, becoming an 

 elongated plate of cartilage which for purposes of convenient refer- 

 ence may be designated Fenestral Plate. If at first it is outside the 

 fenestral tissue, it becomes in the process of growth a part of that 

 structure. Whether the enlargement of the plate takes place through 

 marginal growth with the incorporation of fenestral tissue, or through 

 interstitial growth mth a simple displacement of the bordering mem- 

 brane, has not yet been determined. In late larval life the columella 

 apparently becomes joined to the dorso-cephalic margin of the 

 fenestra by delicate cartilage and subsequently more closely con- 

 nected with the ventro-cephalic edge. Ossification appears late. 

 Two plates of bone are formed, one upon the inner surface of the 

 columella, the other upon its outer surface also extends out upon the 

 stilus. This method of ossification of the columella is quite charac- 

 teristic for other urodeles as well. Fig. 33 (PI. Ill) illustrates 

 the development attained by a 35 mm. larva. 



The condition shortly before transformation is shown in Fig. 

 22 (Plate I), from the model of the ear region in an individual 

 about 45 mm. long. The fenestra vestibuli (F. v.) whose complete 

 outline cannot of course be seen from the figure, is an elongated oval 

 whose dorsal border is formed by the crest of cartilage where the 

 lamina horizontalis of the lateral semicircular canal passes into the 

 lateral wall. For purposes of reference we shall refer to this as 

 the Crista semicircularis (Cr. s.). At the cephalic end of the 

 fenestra the "lips" join to form an elongated prominence with which 

 the processus basalis palatoquadrati articulates. Its interior is occu- 

 pied by a cephalic extension of the cavum perilymphaticum. The 

 caudal end of the fenestra attains nearly the end of the caudal 



