The Columella Auris in Amphibia. 



597 



and free from the ear capsule all round. Although closely associated 

 with, it appears to be wholly outside of, the fenestral membrane. 



At transformation the columella is fused in front with the ear 

 capsule and just fills the opening. Below and behind the columella 

 a portion of the floor of the ear capsule becomes greatly thickened, 

 especially in its lateral half, which is almost completely separated 

 from the capsule (Fig. 19). In this stage there are a few muscle 



Fig. 19. Amphiuma means, transforming larva. (7., arteria carotis in- 

 terna ; O.p., cavum perilymphaticum ; Sq., os squamosum ; V.p-h, vena petroso- 

 lateralis ; M.i.c.i., a portion of the musculus intertransversarius capitis in- 

 ferior. 



fibers partly differentiated off from the M. intertransversarius capitis 

 inferior which have a slight attachment to this portion of the ear 

 capsule. 



This portion of the floor of the ear capsule which was thickened 

 and partly separated off in the transforming individual is in the 

 adult very much thickened, forming the pronounced prominence which 

 encloses an extension of the perilymphatic cavity as shown in Fig. 

 20. The M. intertransversarius capitis inferior comes into close 

 relation with the prominence of the adult, but there is no differentia- 

 tion of a distinct opercular muscle. 



