PROPORTIONS OF THE TECTORIAL MEMBRANE 49 



than the inner that the apical surface of the spiral organ becomes 

 markedly inclined axisward. 



The ideas advanced as to how the spiral organ attains its 

 relative position under the membrane include: (1) that the 

 organ becomes shifted axisward bodily along the basilar mem- 

 brane; (2) that growth in width and thickness of the vestibular 

 lip of the spiral limbus serves to tip and project the membrane, 

 attached upon it, over the spiral organ; (3) that the increase 

 in the size and height of the outer supporting cells (cells of Hen- 

 sen and Deiters) presses the hair cells axisward, causes the 

 apical ends of the pillars to lean axisward and actually slightly 

 displaces axisward the feet of the pillars; (4) that the membrane 

 is produced in its functioning position with reference to the 

 organ instead of there occurring a shifting of position of either 

 the organ or the membrane. 



The latter idea, that the tectorial membrane is produced in 

 situ without changes in its position relative to the hair cells, 

 was naturally one of the first to be advanced. Early discarded, 

 it has been revived by Held and adopted by Prentiss. It re- 

 quires, of necessity, that in the apical turns, the thicker, outer 

 two-thirds of the outspanning zone be produced by the spiral 

 organ, largely after its elements have been differentiated, and 

 by the cells of Claudius (compare figure 7 with figure 2). A 

 stage of development has never yet been described and, I think, 

 never been seen, certainly not in the pig, in which this thicker 

 (and, in the apical turns, by far the greater) part of the mem- 

 brane was being produced by the cells of the differentiating spiral 

 organ and the cells of Claudius. In the pig, and in the pub- 

 lished figures from other mammals, the few sparse, loosely 

 arranged and unsupported fibrils described as produced by the cells 

 of the lesser ridge, attain their maximum amount long before the 

 differentiation of the elements of the spiral organ is completed. 

 They are produced, I think, most rapidly in the pig before the 

 differentiation is well under way. The cells of the lesser ridge 

 have never been seen in a relation to the growing membrane 

 similar to that of the cells of the greater ridge seen in all speci- 

 mens, and further, what is most evidently to be the whole out- 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 18, NO. 1 



