DEVELOPMENT OF THE ORGAN OF CORTI 287 

 DESCRIPTIVE 



Appearance of the tunnel space 



Sections tangential to the surface of the organ of Corti, and 

 always somewhat oblique, affect transversely series of neigh- 

 boring inner and outer pillars at various and successive levels 

 of their length, from the superficial membrana reticularis toward 

 the basilar membrane (fig. 1). As illustrated in figures 1 and 2, 

 one may distinguish in the prismatic lamv-^Uar pillars three 

 portions, although they are not sharply marked off: a basal or 

 nucleated part, the largest, which is lamellar in shape or flattened 

 out in a radial direction from mutual compression; an inter- 

 mediate part; and a superficial part, the narrowest, which is 

 compressed between the inner and outer hair cells, and hence 

 more or less flattened out in a spiral direction {ip and op). The 

 basal and intermediate portions are each made up of two cyto- 

 plasmic zones, the larger being clear and vacuolated, and 

 occupying the area of the cell body close to the future tunnel; 

 the smaller compact and fibrillated, and occupying the axial 

 side of the inner pillar and the lateral side of the outer pillar. 

 The superficial segment of the two rods of Corti contains no 

 vacuolated protoplasm; it consists of a more homogenous, com- 

 pact cytoplasm, which in the inner pillar is traversed by a 

 bundle (fig. 2, ip) or a tubule (fig. 3, ip) of fibrils, and in the 

 outer, encloses a bundle of fibrils which pass between neighboring 

 outer hair cells and give rise to a small band, the phalanx process 

 of the outer pillar (figs. 1, 2, and 3, oph), connected with the 

 superficial apex of the cell, the phalanx. In the adult organ a 

 part of this fibrillar bundle is a characteristic constituent of the 

 superficial portion of the head, and thus its early presence in a 

 definite portion of the outer pillar is very important in enabling 

 one to determine, from the earliest stages of development, a 

 very narrow but long superficial portion of the cell (figs. 1, 2, 

 and 3, op), which later enlarges and becomes transformed into a 

 part of the bulky head. It is also obvious that the adjoining 

 portion of the inner pillar, which in figures 1, 2, and 3 is in close 

 contact with this future head of the outer pillar, must be con- 



