PROPORTIONS OF THE TECTORIAL MEMBRANE 45 



inner supporting cells of the spiral organ. As such, they re- 

 tain to an extent their outwardly reclining direction. In the 

 recession and disintegration of the cells, the decrease in number is 

 such that the cells (nuclei) in the greater epithelial ridge of the 

 apical turns at 15 to 16 cm. are twenty to twenty-five times the 

 number of the cells which line the internal spiral sulcus and com- 

 prise the inner fourth (the smaller supporting part) of the mature 

 spiral organ. Held and others before him have shown for other 

 mammals that the retrogression and disintegration of the cells 

 of the greater ridge begins at the axial edge of the ridge and pro- 

 ceeds outward, thus freeing from attachment first the axial bor- 

 der of the outspanning zone of the tectorial membrane; and 

 Prentiss notes that the "inner half of the spiral organ" (inner 

 supporting cells) is derived from the greater ridge. 



The inner supporting cells, during their differentiation from 

 the cells of the greater ridge recede slightly. Then they increase 

 in both height and size in the increase in the size of the spiral 

 organ so evident in the apical coils of the adult hog. However, 

 as shown in the figures and as will be noted below, the outer 

 supporting cells (cells of Hensen) increase in height and size 

 considerably more than the inner during the growth of the 

 apical regions of the organ. The cells of Claudius also decrease 

 slightly in height and increase in width between the earlj^ 

 fetus and the adult form of the spiral organ. The decrease 

 in height seems to result from loss in their distal ends, for the 

 nuclei are situated earlier in the middle and proximal (or basal) 

 ends of the high columnar cells and later in the distal ends of the 

 low columnar and cubic cells. In the adult, the cells of Claudius 

 appear to increase considerably in height in passing from the 

 apical to the basal end of the cochlear duct. It may be sug- 

 gested that both the spiral organ and the cells continuous with 

 it, though their differentiation is completed earliest in the basal 

 end, do not undergo so extensive differentiation in the basal 

 as in the apical end; (compare figures 1 to 4). Further, from 

 study of the different stages of development, it seems probable 

 that at least four cells of the lesser ridge take' part in forming 

 the boundary of the tunnel of the spiral organ in a given section 



