The Columella Auris in Amphibia. 557 



cupola of the otic capsule. It may be noted that the fenestra vesti- 

 buli is in the lateral wall of the ear capsule, becoming more ventral 

 in its cephalic portion. 



The fenestral plate occupies the larger portion of the window, 

 being most widely separated from the margin of the fenestra at its 

 caudal end. In the model the relations of the arteria carotis interna 

 and vena petroso-lateralis are shown crossing and partially covering 

 the fenestral plate. In Fig. 2o (Plate I), however, in a somewhat 

 later stage, the complete outline of the fenestral plate can be seen. 

 At the cephalic end, on both ventral and dorsal margins, new car- 

 tilage, not shown in the model, is just beginning to join the columella 

 to the margin of the fenestra vestibuli. The stilus and ligament con- 

 nect the fenestral plate with the ventral edge of the squamosum. The 

 palatoquadrate cartilage does not become connected mth the liga- 

 ment. A blunt process of the quadrate underlying the squamosum 

 is not brought into relation with the ligament at this stage. 



At transformation the fenestral plate becomes joined to the lips 

 of the opening on all sides save the caudal and the caudal portion of 

 the ventral side. There is, however, a portion of the primary fenestra 

 behind the stilus where even in the fully grown salamander the wall 

 of the otic capsule is very thin, — membranous or filled in with a thin 

 lamina of cartilage (See Fig. 24, PL I, 'T"). In Fig. 23 the 

 outlines of the old fenestral plate still shows. The delicate new 

 cartilage just forming was not modeled. In Fig. 24, the fusion 

 of the plate with the edge of the fenestra is nearly complete. The 

 outline of the old columella and the newlv formed cartilage can be 

 distinguished. 



In the process of transformation, due to the shifting of the sus- 

 pensorium, the attachment of the stilus becomes largely transferred 

 from the squamosum to the palatoquadrate cartilage (PI. I, Fig. 24). 



The operculum present in the transformed salamander (PI. I, 

 Fig. 24, Op.; PL II, Fig. 25) occupies the caudal portion of the 

 new fenestra (definitiva) whose dorso-cephalic margin includes the 

 cephalic end of the operculum ; the caudal end projects freely and 

 to it is attached the M. opercularis whose tendon fits into and fills 

 a depression upon its external surface (PL IV, Fig. 35). 



