The Columella Aiiris in Amphibia. 563 



Winslow ('98), on the other hand, has described and figured models 

 of three stages of the chondrocranium of Ambystoma. He describes 

 the columella (Stapes) chondrifying as an independent center in a 

 12 mm. individual. The condition in a 37 mm. larva he describes 

 as follows: ''The fenestra ovalis is now nearly filled by the stapes 

 (s), which has a slight prominence directed outwards and upwards 

 from the antero-dorsal angle of the cartilage towards the otic process 

 of the quadrate. These cartilages, however, do not become united 

 at any time during the development of Ambystoma as they do in 

 some other forms." In a young adult, 69 mm. in length, he de- 

 scribes the stapes as in the posterior portion of the fenestra closely 

 applied against the remnant of the cartilaginous wall of the capsule, 

 this time describing the operculum as stapes. His figure bears out 

 the brief description and shows the stilus of the fused columella 

 extending from the ear capsule to the palatoquadrate. 



It is hardly necessary to comment on the difficulties of interpre- 

 tation in such a form as Ambystoma if the changes at transformation 

 are ignored. Transformation occurs relatively quickly and at this 

 time the salamanders are less easily procured. 



Chondi-otus tenebrosus. Three examples of this species were 

 examined ; larval, transforming, and adult. It was not surprising 

 to find that the relations in this salamander closely resembled those 

 in Ambystoma l^ecause of the close relationships of the two genera. 



The laiwa was well advanced (58 mm. long) and the morphological 

 relations diagrammatic in their clearness. The otic capsule as also 

 the remainder of the chondrocranium is unusually heavy, and the 

 columella shares this characteristic. As shown in Fig. 34 (PI. 

 Ill) there is a well developed stilus which articulates closely with 

 the lower edge of the squamosum. In no other form examined by 

 us has a single section shown the distal connection as well as the 

 central origin of the stilus from the fenestral plate, as a result of 



a ligament arises wliich spreads into a fan-like fascia, which is inserted 

 along the under and outer edges of the suspensorium from the lohe of the 

 otic process to the lobe of the quadrate ... it lies some height above 

 the portio dura. . . ." Page 562. "Thus we have here what may be 

 called a spiractilar fascia, the counterpart of the spiracular cartilage and 

 bone of the Menopome and others." 



