GROWTH OF THE INNER EAR OF ALBINO RAT 9 



wall of the cochlea are somewhat complicated, but by the aid 

 of figures 1 and 2 they may be explained. In figure 1 lines 1-1, 

 1-1'. 2-2, 3-3 indicate, respectively, the height of the arch of 

 Corti, of the tunnel of Corti, of the papilla spiralis (Huschke) at 

 the third series of outer hair cells, and of Hensen's supporting 

 cells, respectively, above the plane of the membrana basilaris. 



Lines 4-4' which are the extensions of the surface of the lamina 

 reticularis and of the membrana basilaris, subtend the angle 8. 



To get the exact measurements of the radial breadth of the 

 membrana tectoria is very difficult, if not impossible, because it 

 is sinuous in its course; moreover, it differs in thickness from 

 point to point. Therefore, it has been variously described by 

 different authors. Intra vitam fixation tends to prevent dis- 

 tortion. We divide the membrana tectoria, figure 1, into two 

 portions, the first or inner (7-7'-9-9') and the second or outer 

 (5-5 '-7-7') or outer zones of Retzius; each of these is again 

 divided in two at 6-6' and 8-8', as shown in figure 1. 



I have measured the radial distance of each portion and added 

 all four together. This total approximates the natural radial 

 breadth of this membrane, and since the sections have all been 

 prepared in the same way and examined by the same method, the 

 relations during growth can be followed. 



In figure 2, 1-1 and 2-2, mark the length of the inner and outer 

 pillar cells, respectively, from base to the point, which is situated 

 just under their junction. It is to be noted here that the term 

 ' pillar cell ' here applies to the pillars in the strict sense and does 

 not include the associated cells. 



Distances 3 and 7 in figure 2 show the basal breadth of the 

 inner and outer pillars, respectively. The former is identical 

 with the distance between the habenula perforata and the outer 

 corner of the inner pillar after the inner corner of the pillar has 

 reached the habenula perforata, but there is some difference 

 between the two distances in very young rats. Distance 4 is 

 that between the habenula perforata and the inner corner of 

 the outer pillar; distance 5 is that between the habenula per- 

 forata and the outer corner of the outer pillar. The latter rep- 

 resents at the same time the radial breadth of the zona arcuata 

 of the membrana basilaris. 



