136 ARRANGEMENT AND STRUCTURE OF SUSTENTACULAR CELLS 



row, and of those of the outer sustentacular elements towards the axis of the cochlea 

 and into interstices between the primitive rows; so that three new spiral rows or 

 spaces make their appearance. Indeed, each original mixed spiral row becomes 

 divided into two a medial or inner supporting column, and a lateral, purely sen- 

 sory column. Hence the first mixed spiral row of outer hair-cells is divided into a 

 column composed of parts of outer pillars and a column of acoustic elements; the 

 second mixed spiral row of outer hair-cells is divided into a column composed of 

 parts of the cells of Deiters of the first row and a column of acoustic elements; the 

 third mixed spiral row of outer hair-cells is divided into a column composed of parts 

 of the second row of Deiters cells and a column of acoustic elements. 



4. The original membrana reticularis is formed of seven very distinct spiral 

 rows of fields, the apices of the subjacent cells, which are separated from one another 

 by terminal bars. When each of the three outer mixed spiral rows becomes double 

 near the surface of the epithelium, two spiral intervals appear within the lamina 

 reticularis, one between the apices of the hair-cells of the first and second rows, and 

 the other between the apices of the acoustic elements of the second and third rows, 

 these intervals being covered by portions of the neighboring elongated phalanges. 



5. A fundamental principle governs the arrangement of the supporting elements 

 during the earliest stages of development of the organ of Corti. By compression 

 from neighboring constituents the cell body may become shifted, but the base, 

 which is attached to the membrana basilaris, and the apex interpolated within the 

 membrana reticularis, remain fixed. These may enlarge with the extension of the 

 membranae, but there is never any shifting. 



6. The second stage of development is characterized by the shifting of the 

 nucleated cell bodies of the outer supporting elements from their original spiral row; 

 that is, from beneath the hair-cells of that row, inward and to a point just below the 

 superficial, supporting interstices appearing in the first stage of development; so 

 that the latter now constitute complete spiral rows extending throughout the thick- 

 ness of the epithelium, whereas the three original mixed outer rows are converted 

 into a purely sensory one, occupying the superficial two-thirds of the epithelium. 

 External to the inner pillars, from the axis of the cochlea towards the outer part of 

 the lesser ridge, there exist the following spiral rows: One of outer pillars, the first 

 row of outer hair-cells, the first row of cells of Deiters, the second row of outer hair- 

 cells, the second row of cells of Deiters, the third row of outer hair-cells, and the 

 third row of cells of Deiters, the nucleated cell bodies of which show a tendency 

 to shift below the neighboring acoustic elements. 



7. The shifting of the nucleated portions of the outer supporting cells is the 

 result of several mechanical factors: (a) The appearance of an axial framework 

 within the organ of Corti represented by two kinds of rods of Corti. By the basal 

 extension of this framework the bases of J||he cells of Deiters are pressed outward 

 much more than is the apical portion of their nucleated cell bodies. (6) The 

 broadening and lengthening of the outer hair-cells, which is possible only towards 

 the outer side of the lesser ridge. The summit of the nucleated portion of the 



