126 AERANGEMENT AND STRUCTURE OF SUSTENTACULAR CELLS 



or cubical elements (fig. 15, esp), while close to the inner hair-cells a few retain their 

 original, elongated form (figs. 15 and 17, nd), the latter being erroneously termed by 

 some investigators, inner supporting cells. Indeed, they represent undifferentiated 

 epithelial elements, and in the cochlea of most adult mammals their number is 

 reduced to that of the true inner supporting cells. The character of these elements 

 and the relation they bear to the neighboring sensory elements should be more 

 accurately investigated. Most authors agree also that, during this stage of develop- 

 ment, when the sulcus spiralis is being built up, many of the columnar cells undergo 

 degeneration and disintegration, although very few observers are able to picture or 

 even describe such a process. In the cochlea of the dog, cat, rabbit, and ox two 

 distinct regions should be distinguished. One of these is medial, the true sulcus 

 spiralis (fig. 15, esp), where not the slightest evidence of cell disintegration is ever 

 seen, the high, columnar cells becoming gradually shorter, larger, and flattened out 

 to cover the sulcus, which at first is narrow, but which subsequently, as the lumen 

 of the duct enlarges, acquires considerable size. The other is lateral, just inside of 

 the inner hair-cells (figs. 15 and 17, ih) or the foramen nervinum (N), where the 

 columnar cells (nd) persist for a long time, and where occasional elements may 

 undergo chromatolysis (fig. 17, ch), while most, if not all, of the others become con- 

 verted into larger and shorter lining-epithelium cells. 



External to, or even partly encroaching upon the foramen nervinum (figs. 15 

 and 17, N), are found the two rows of inner supporting cells already referred to as 

 belonging to the first inner mixed and second inner supporting spiral rows. In the 

 course of development the inner supporting cells undergo no marked shifting or 

 cytoplasmic differentiation. In this respect they differ from the cells of Deiters, 

 although resembling the latter and possessing many of the same essential charac- 

 teristics; for example, (1) original connections with the hair-cells, (2) number, and 

 (3) the shape of their free apices. 



(1) The first inner row, like the three outer spiral rows, or'ginally is a mixed 

 row of sensory and sustentacular elements, and remains so, the supporting elements 

 being entirely inclosed within the spiral row and running through the intervals 

 between the hair-cells. Moreover, the free apex of the sustentacular elements, 

 interpolated within the membrana reticularis, is more or less phalanx-shaped. The 

 inner supporting cells of the second row, like the cells of Deiters of the third row, 

 belong to a spiral row purely sustentacular in character; but whereas the latter, 

 after a process of shifting, become transformed into a true sustaining framework for 

 the neighboring hair-cells, the former preserve their original position. In other words, 

 the two rows, the second inner and fourth outer, are originally boundary rows of the 

 organ of Corti. The former does not change in its nature, but the latter develops 

 into a true sustentacular row, at least as regards the cell bodies of its components. 



(2) As to the inner supporting cells of the first row, no doubt can be entertained, 

 the spiral row being composed of alternating sensory and sustentacular elements, and 

 their number exactly the same as that of the supporting cells of each of the three 



