434 C. W. PRENTISS 



other cells which are forming the membrana continue to secrete 

 actively. At the same time these cells by growth and multipli- 

 cation increase the width of the basal epithehum, carrying the 

 spiral organ outwards. Thus the distance from the inner angle 

 of the cochlear duct to the spiral tunnel is increased. In the 

 second spiral of the 5.5 cm. stage as in figure 2 this distance is 

 140 ju- In the 8.5 cm. stage the same distance is about 280 m- 

 Cells near the pillars of Corti which are secreting the membrane 

 may thus be carried outward approximately 140 m, while that 

 part of the membrane first formed does not grow. As the so- 

 called 'lamellae' are secreted at the ends of the cells and the cells 

 are shifted outward as the lamellae lengthen, naturally the bases 

 of the lamellae will also be carried outward while their tips 

 remain stationary. The inward trend of the lamellae from base 

 to tip is thus satisfactorily accounted for. 



It may be well to emphasize here the fact that the greater 

 epithelial thickening gives rise not only to the epithelium of the 

 labium vestibulare and of the spiral sulcus but also to the inner 

 axial half of the spiral organ, including the inner supporting 

 cells, and possibly the inner hair cells and inner pillars. This 

 is in agreement with the results of Coyne et Cannieu ('95) and 

 Rickenbacher ('01) Van der Stricht and Held ('09). Hardesty 

 states that ''the lesser thickening is the first indication of the 

 differentiation of the organ of Corti while the cells of the greater 

 give origin to the tectorial membrane .... and the low 

 indifferent cells lining the spiral sulcus." This misinterpretation 

 is important as it partly accounts for his later statement that 

 the memhrana is not derived from the cells of the spiral organ. 



The next question to decide is the true structure of the mem- 

 brana tectoria. Is the membrane composed of lamellae or hairs 

 or fibers or is it a reticulum? If it is formed at the ends of the 

 cells just how is it developed there? These points were decided 

 by a study of later stages, the cochleae of a 13 cm. fetus prov- 

 ing most favorable material. In the various cochleae which 

 were examined it was found that differentiation begins in the 

 basal turn and is much less advanced in the upper turns. Thus 



