AND HAIR-CELLS IN THE DEVELOPING ORGAN OF CORTI. 117 



FIRST STAGE OF DEVELOPMENT. 



In figure 2 is illustrated a section tangential to the surface of the apical or first 

 turn of the cochlea in a dog 12 hours after birth. Between the inner and outer hair- 

 cells is seen a column of distinct, nearly square fields cross-sections of a series of 

 inner pillar cells (ip) . The lowermost third of this column is nucleated and belongs 

 to six pillars cut at six different levels. From mutual compression, together with 

 an enlargement of this basal portion of the cell, the nucleus and its surrounding- 

 protoplasm are somewhat flattened out in a radial direction. The upper two-thirds 

 of the column becomes gradually smaller and contains a darker, axial, granular strand. 

 The clear superficial field of the column the true apex of the cell is the narrowest 

 and incloses a central corpuscle. From this it is clear that the inner rod of Corti 

 is a columnar cell, a four-sided prism in shape, enlarged at its base and tapering to 

 its free surface. In more advanced stages (figs. 3 and 4) the enlargement and 

 flattening of the basal portion of the cell are more marked, the apical portion 

 thinner, while the intermediate, true cytoplasmic part increases in size. 



Close to this spiral row of inner pillar cells, and situated within the greater 

 ridge, may be seen (figs. 2, 3, and 4) cross-sections of three different rows of cells; 

 one row of inner hair-cells (ih), and two rows of inner .supporting cells (is 1 , is"). 

 The former extend through the superficial two-thirds of the epithelium and possess 

 a dark, granular, and considerably increased cytoplasm with large nuclei in the 

 lower portion of the cell. At the free surface of the cell is an eccentric, central 

 corpuscle surrounded by a clear area the medullary zone of the attraction sphere 

 of Ed. Van Beneden, and a deeply staining plate the superficial cuticula or the 

 cuticular plate (N. Van der Stricht), from which the hairs arise. 



Just below the cell bodies of the inner hair-cells lies the basal portion of the 

 inner sustentacular cells of the first row (figs. 2, 3, 4 and 10, is 1 ), composed of a 

 smaller nucleus and a clearer protoplasm, which reaches the surface of the epithelium 

 by means of a long cytoplasmic process, running between and compressed by the 

 enlarged hair-cells. Being a four-sided prism at the level of its nucleated basal 

 part, this columnar cell becomes lamellar, flattened out in a radial direction at the 

 level of the acoustic elements (figs. 2 and 10), and by compression between two 

 neighboring cells is pushed toward the inner pillars, its form being triangular on 

 section, at first near the nucleated portion (figs. 2 and 3), and later also near the 

 superficial cytoplasmic part of the inner hair-cells (fig. 4) . Thus it is clearly seen that 

 the inner supporting cells of the first row do not run laterally, either inside or outside 

 of the inner hair-cells, but course through an interval between two acoustic elements, 

 and by enlargement of the developing hair-cells are pressed towards the outer or 

 lateral part of this interstice to take again their original position just beneath the 

 superficial membrana reticularis. 



The inner supporting cells of the second row (figs. 2 and 3, is") are four-sided 

 prisms, composed each of a small basal nucleus and a clear cytoplasm. These cells 

 undergo no compression from intermediate cells, but form a distinct spiral row, 

 constituting the inner boundary of the organ of Corti, just as the cells of Deiters of 

 the outer third row (figs. 2 and 3, d 111 ) constitute the outer limit of the spiral organ. 



