116 ARRANGEMENT AND STRUCTURE OP SUSTENTACULAR CELLS 



thelial thickening forms the external portion of the spiral organ. But at present 

 no doubt exists as to the origin of these structures. According to Rosenberg (1868), 

 Gottstein (1871), Boettcher (1872), Retzius (1884), Denis (1901), Vernieuwe (1905), 

 N. Van der Stricht (1908), and Held (1909), the inner hair-cells originate from the 

 greater ridge, all the pillars and outer hair and supporting elements from the lesser 

 ridge; Rosenberg, Vernieuwe and Held locating the inner rods of Corti in an inter- 

 stice outside the greater ridge between the two epithelial thickenings. 



The superficial membrana reticularis of the organ of Corti has been referred to 

 in a previous paper (1918). 



It is evident from the above review that most of the structures of the spiral 

 organ are at present well known. Nevertheless, many others require further inves- 

 tigation, and of these, four types will be dealt with herein, i. e.: 



(1) The connections between the outer supporting cells and the hair-cells. If 

 the view taken by N. Van der Stricht be correct, and the nucleated body of the 

 sustentacular cell undergoes gradual shifting, what happens to its more super- 

 ficial segment? What is its exact location during the three successive stages of 

 development? What mechanical factor causes this alteration in the position of the 

 cell body? At what period of development, and in what manner, does the spiral 

 shifting of the apical process of the cell of Deiters take place? 



(2) The connections between the inner hair-cells and their sustentacular ele- 

 ments. 



(3) The significance of some of the so-called cells of Hensen. 



(4) The nature and origin of peculiar, coarse structures in the cyptoplasm of 

 the hair and supporting cells. 



CONNECTIONS BETWEEN THE OUTER SUPPORTING AND HAIR-CELLS. 



In the new-born dog the epithelium of that part of the spiral membranous 

 duct which lies close to the apex of the cochlea is still undifferentiated and is composed 

 of elongated columnar cells, the apices of which reach the surface. A section tan- 

 gential to these free ends shows a regularly formed mosaic of small, undifferentiated 

 polygonal fields, each of which contains a diplosome. The polygons are separated 

 from one another by terminal bars (referred to in a previous paper, 1918). On 

 tracing the pattern through a series of sections, more and more remote from the 

 summit of the cochlea, different structures are successively met with. First, within 

 the greater ridge appear the inner hair-cells, recognizable by the enlargement of 

 their cell bodies and nuclei, while in a section tangential to the surface their apices 

 are seen in the form of rounded, sensorial fields, quite different from the neighbor- 

 ing supporting and non-differentiated polygons. Somewhat farther from the apex 

 of the cochlea the outer hair-cells become differentiated and constitute the lesser 

 epithelial thickening; there is an increase in the cytoplasm and the size of the 

 nucleus, and the latter, like that of the inner sensory cells, stands out prominently 

 in the vicinity of the epithelial surface, whereas the nuclei of the future supporting- 

 elements persist near the basilar membrane. 



