AND HAIR-CELLS IN THE DEVELOPING ORGAN OF CORTI. 135 



rise to the thick, firm terminal bars which close the spaces and separate them from 

 the endolymph of the cochlea duct. By close examination of figures 3, 4, 5, 7, 9, 

 and 11, it is obvious that the vacuolization of the sustentacular elements becomes 

 more pronounced as the basilar membrane is approached, and that the chief sup- 

 porting cells the inner and outer pillars at first undergo considerable enlargement 

 and acquire a markedly vacuolated structure quite close to the subjacent vas 

 spirale (vs). which rapidly increases in size along with the transformations just 

 described. Later, when the definite structures of the organ of Corti are nearly 

 built up, the vas spirale becomes reduced in size (figs. 4, 16, and 15, vs). These 

 facts furnish abundant evidence to support the theory that the fluid contained 

 within the meshes of the network, or the contents of the vacuoles within the cyto- 

 plasm of the supporting elements, is derived from the blood of the vas spirale by 

 means of a process of exudation through its endothelial wall and the adjoining base- 

 ment membrane. This food supply, stored in the cytoplasm of the sustentacular 

 cells, may undergo further glandular or chemical alteration before being utilized in 

 the building up of the apparatus of support of the rods of Corti and the cells of 

 Deiters, and transferred to the neighboring hair-cells. 



SUMMARY. 



1 . The first stage in the development of the organ of Corti is characterized by 

 the existence of seven sharply marked, spiral rows of cells. Of these the inner pillar 

 cells and two boundary rows i. e., the second inner row of supporting elements and 

 the third row of Deiters cells are purely sustentacular in character. The remain- 

 ing four are mixed rows, being composed of alternating sensory and sustentacular 

 elements, and constituting the row of so-called inner hair-cells and the three rows 

 of so-called outer hair-cells. The hair-cells extend through the superficial two 

 thirds of the epithelial layer, and are separated from each other by the cytoplasmic 

 portions of their respective sustentacular elements, the basal, larger, nucleated part 

 of which fills the space between the hair-cells and the basilar membrane, as illus- 

 trated in figure 22 (is 1 , ih). In sections tangential to the surface each of the four 

 mixed rows is seen in the form of two nucleated columns; one, the column of exclu- 

 sively supporting elements, near the basilar membrane; the other, the column of 

 alternating sensory and sustentacular elements, near the surface of the epithelium. 



2. The original four mixed spiral rows are formed as follows: (a) The row of 

 inner hair-cells is composed of inner acoustic elements and inner supporting ele- 

 ments; (6) the first row of outer hair-cells, of outer acoustic elements and outer 

 pillar-cells; (c) the second row of outer hair-cells, of outer acoustic elements and the 

 first row of Deiters cells; (d) the third row of outer hair-cells, of outer acoustic ele- 

 ments and the second row of Deiters cells. 



3. The superficial cytoplasmic two-thirds of the supporting cells of the mixed 

 spiral rows undergoes compression from the rapidly enlarging neighboring acoustic 

 elements. This pressure results in a flattening and subsequent shifting of these 

 portions of the inner supporting cells towards and into the lateral part of the spiral 



