AND HAIR-CELLS IN THE DEVELOPING ORGAN OF CORTI. 121 



as illustrated in figs. 19, 19', 20, 21, and 23. These are diagrams of vertical spiral 

 sections through the outer spiral rows. In figures 19 and 19' there can be seen to 

 the left a more basal portion of the second turn of the cochlea in a new-born kitten, 

 and to the right a more apical portion, consisting of the following elements : A series 

 of acoustic cells of the first outer row (oh 1 ) recognizable by the presence, between the 

 apices of the hair-cells of a bundle of fibrils (op) emanating from the heads of the 

 outer pillars; a series of acoustic elements of the second outer row (oh"), and a series 

 of hair-cells of the third row (oh m ). The clearer intervals filled with longitudinal 

 tangential sections through the lateral surfaces of acoustic elements, and situated 

 between the first and second, between the second and third row, and at the end of 

 the third row (compare with figs. 20 and 21) are respectively the first, second, and 

 third outer sustentacular interstices. 



Below these sensory elements are seen three series of the nucleated portion of 

 the cells of Deiters of the first (d'), second (d") and third (d m ) rows; these are con- 

 nected with the membrana reticularis by a thin, superficial phalanx process, running 

 obliquely through their respective interstices (fig. 20, d 1 , d u ). In the three turns 

 of the cochlea in the kitten, young dog, and young rabbit these apical processes 

 always course regularly below upward, and from a more basal to a more apical por- 

 tion of the turn, crossing the medial side of three hair-cells (figs. 19, 21, oh", d ! ; 

 oh i!i , d"), or the lateral side of the hair-cells of the third row (fig. 19', oh" 1 , d" 1 ). 



From the above description it is clear that during the second stage of devel- 

 opment the cells of Deiters undergo a shifting in two directions one axial, from 

 without inward; the other spiral, from the base of the cochlea upward and toward the 

 more apical portion of it. What mechanical factors are involved in this process? 

 The chief framework around which the constituents of the organ of Corti are built 

 up is undoubtedly the original single spiral row of inner pillar-cells (fig. 2, ip). Very 

 early this framework becomes stronger, owing to the appearance of an additional 

 row of outer pillars (figs. 4 and 5, ip, op) ; and although the inclination of these two 

 kinds of rods of Corti is liable to change, the axis of the framework (figs. 1, 3, 4, 5, 

 and 14), even when the tunnel space is present (figs. 15, 16, and 17, T), is more or 

 less perpendicular to the basement membrane and passes through a part of the 

 lumen of the vas spirale (vs). As development progresses, this spiral framework 

 becomes more and more wedge-shaped or triangular in sections, the summit of the 

 triangle being formed by a very narrow field the apex of the inner pillar (figs. 2, 5, 

 and 15, ip), so long as the tunnel space is not developed, and the broad base of the 

 triangle consisting of the adjoining feet of the inner and outer rods of Corti. As the 

 result of this rapid and considerable extension of the base, the deepest part of the cells 

 of Deiters, although immobile on the basilar membrane, is removed farther from the 

 axis of the framework. On the other hand, by comparing the illustrations of the 

 membrana reticularis in figures 4, 10, and 18, the lateral extension of this is rather 

 i nconspicuous and the apices of the outer supporting cells do not follow the lateral 

 shifting of their bases. The result is that the direction of the nucleated supporting 

 columns seen in figures 2, 3, and 4, (op, d', d u , d 1 "), lying just beneath their respective 

 columns of supported sensory elements (oh 1 , oh", oh 1 ") will change, their bases 



