56 IRVING HARDESTY 



apical turn. At the basal end, the greater ridge remains narrower 

 and produces the narrow end of the membrane. Where the 

 greater ridge is widest, there the membrane is produced widest, 

 the reduction in the cells of the ridge is greatest, the enlargement 

 of the outer supporting cells is greatest, and there, as a result, 

 the change axisward of the spiral organ is greatest. 



Prentiss states that measurement "shows no important change 

 in the position of the spiral organ from the 13 cm. to the 18.5 

 cm. stage, nor later in the newborn" pig. He allows the in- 

 ference that he measured "the distance between the inner angle 

 of the cochlea and pillar cells," but gives no records of measure- 

 ments. His averages for the 13 and 18.5 cm. stages and those 

 for the newborn pig would have been interesting for comparison 

 with like measurements that could be made in the specimens 

 used here. On page 434 he describes the greater ridge as in,- 

 creasing in width by growth and multiplication of its cells, "car- 

 rying the spiral organ outwards," while he denies in other pas- 

 sages the possibiUty of the spiral organ being carried axisward. 



With the completion of the retrogression and disintegration 

 of the cells of the greater ridge and the simultaneous movement 

 axisward of both the entire spiral organ and its apical surface, 

 the thick, outspanning zone of the tectorial membrane, of neces- 

 sity, becomes free. The few loosely arranged fibrils, produced 

 by the lesser ridge before its completed differentiation into the 

 spiral organ, may persist and remain attached to the outer 

 edge of the membrane till torn asunder in the freeing process. 

 There is no evidence of them on the membrane of the adult. 

 In the fetus at term, when the process of freeing is being com- 

 pleted, it is possible that remnants of them may at times adhere as 

 a delicate plexus to the outer edge of the membrane. 



It is possible that the outer margin of the tectorial mem- 

 brane, which, during its production, cups around the outer part 

 of the greater ridge, may straighten outward slightly upon being 

 freed. If so, such behavior would contribute sUghtly to the 

 projection of the membrane beyond the spiral organ. 



The thin axial zone remains attached upon the vestibular lip 

 of the spiral Umbus. The cells producing this are never thick. 



