292 O. VAN DER STEICHT 



Outer jpillars. In the superficial part of the entirely de- 

 veloped outer pillar, as seen in the adult organ of Corti, three 

 different portions are distinguishable: 1) The apex or 'phalanx,' 

 fonning a part of the membrana reticularis. This consists of a 

 lateral, expanded segment (fig. 8, oplv), which constitutes a 

 portion of the roof of a subjacent intercellular interstice, through 

 which course the phalanx processes of the cells of Deiters of the 

 first row (paper in press); and a medial, constricted segment 

 (op/i") lying just between two apices of the outer hair cells of 

 the first row {oh>). 2) A fibrillated band or the phalanx process 

 (fig. 13'", oph\ oph", oph'''), which runs nearly horizontal and 

 unites the apex to the head. 3) The head proper, or the en- 

 larged superficial part of the pillar, in contact with the inner 

 pillar (figs. 13''^, 17, and 18, ohd). This is a cubical segment; 

 in sections tangential to the surface it is square (fig. 13'", ohd) 

 or somewhat lengthened out radially (fig. 18, ohd). Its upper 

 portion is traversed by the fibers of the phalanx process (fig. 17, 

 ohd), and its larger, lower part by a fibrillar bundle belonging 

 to the body of the pillar (fig. 13'^, ohd). Thus two different 

 fibrillated fasciculi spread out, and fade off into the head; there 

 is no direct continuity between the fibrils of the two bundles 

 (figs. 14 and 15, ohd). 



In the first stage of development, which may last until the. 

 tunnel space is about to appear and before there is any marked 

 increase in the site of the future head (figs. 1, 2, and 3, op), the 

 three parts of an adult pillar just referred to are recognizable. 

 The apex acquires the appearance illustrated in figure 4, oph. 

 The phalanx process is short and a nearly vertical, dejeply 

 stainmg bundle of fibrils (figs. 1 and 3, oph) which is traceable 

 between the cell bodies of the outer hair cells {oh'), and a little 

 deeper between these sensory elements and the future head. 

 The future head is a thin tapering part of the pillar, composed 

 of a more or less homogeneous cytoplasrh which encloses in its 

 upper two-thirds the rootlets of the phalanx fibrils, and in its 

 lower one-thu'd the summit of the bunch of fibrils of the pillar 

 body (figs. 2 and 3, op). Indeed, in figures 1, 2, and 3, two or 

 three fields, cross-sections of the future head, contam parts of 



