118 ARRANGEMENT AND STRUCTURE OF SUSTENTACULAR CELLS 



Outside of the inner pillars the organ of Corti, in the earliest stages of its devel- 

 opment, when the outer superficial sensory fields (fig. 10, oh 1 , oh", oh'") have 

 attained about half the size of the inner (fig. 10, ih), is formed of four spiral rows 

 (figs. 2, 3, and 10) : (1) The first row of outer hair-cells and outer pillar-cells (oh ; , op) ; 

 (2) the second row of outer hair-cells and cells of Deiters of the first row (oh u , d') ; (3) 

 the third row of outer hair-cells and cells of Deiters of the second row (oh iu , d") ; (4) 

 the cells of Deiters of the third row (d iu ) . The outer hair-cells correspond with the 

 inner in structure, except that their development and enlargement begin somewhat 

 later, and that even in the adult cochlea their size is smaller. The outer pillar-cells and 

 the cells of Deiters of the first and second rows are similar to the inner supporting 

 cells of the first row in number, arrangement, and structure. Their cytoplasm is 

 clear, and their nuclei occupy the basal one-third of the cell. 



In sections tangential to the free surface of the epithelium these nucleated 

 portions of the supporting cells are juxtaposed into nuclear columns, and, like the 

 nuclear column of the inner sustentacular elements of the first row, lie directly 

 beneath the acoustic cells of their respective columns. The superficial two-thirds 

 of these outer supporting elements reach the membrana reticularis, running through 

 the interval between two developing hair-cells by which they are compressed, so that 

 the original four-sided prism (fig. 10, op) becomes flattened out in a radial direction 

 (fig. 3, op, d 1 , d"), and assume a lamellar, pentagonal (fig. 3) or triangular (fig. 2) 

 shape on section. As the result of mechanical pressure from the neighboring hair- 

 cells, which gradually increase in sue chiefly in their nucleated portion, the super- 

 ficial cytoplasmic processes of the outer pillars and the cells of Deiters of the first 

 and second rows are compressed and pushed toward the medial side of their respec- 

 tive spiral rows that is, toward the inner pillars, the superficial portion of which 

 is thereby flattened out. The subsequent shifting of this compressing process 

 becomes conspicuous, first at the level of the enlarged nucleated parts of the hair- 

 cells (fig. 3, op. d 1 , d a ), afterwards in the more superficial region (fig. 2). 



This gradual, mechanical shifting of the upper two-thirds of these supporting 

 cells ultimately results in their transposition into a system of new spiral rows or 

 spaces as follows: (1) A spiral row of outer pillar cells situated between the spiral 

 row of inner rods of Corti and the first row of outer hair-cells. This is illustrated in 

 figure 4, showing the upper part of the outer pillars pushed inward from their 

 original spiral row. This apical portion is increased in size and pentagonal in 

 shape on section, and its outer angle still encroaches upon the original row, mainly 

 close to the surface where it is connected with the phalanx or the apex of the outer 

 pillar-cell, always interpolated within the primitive first outer spiral row. (2) A 

 first outer interstice situated between the first and second rows of outer hair-cells 

 (fig. 4, d 1 ). (3) A second outer interstice situated between the second and third 

 rows of outer hair-cells (fig. 4, d") . The first and second outer interstices contain 

 respectively the phalanx processes of the cells of Deiters of the first and second 

 rows. These processes for a time may encroach upon their original sensory row, 

 but later are entirely incorporated within their ultimate interstice except close to 



