204 AYERS. [Vol. VI. 



ject freely between the processes. In later stages of develop- 

 ment it is demonstrable that these processes are fixed to the 

 upper end plates of Deiters's cells, i.e. the phalanges. 



In the basal and middle spires the lamina spiralis is much 

 more developed than in the apical, and the peculiar transforma- 

 tion of the large ridge has begun, the cells of the ridge disap- 

 pear from within outwards, their places being taken by cubical 

 epithelial cells. By this means a split appears between the 

 membrana tectoria and the epithelial surface, which grows pro- 

 gressively towards the cochlear apex. The large ridge is highest 

 in the apical turn, and is at this time in the height of its de- 

 velopment. 



The inner hair cells lie more inclined outwards than before 

 and have increased in size, at the same time taking on more of 

 the adult appearance. 



The pillar cells are in a very interesting stage of their devel- 

 opment. In the apical turn they are closely placed and do not 

 show signs of separation. They are both inclined outwards ; 

 they have grown much in radial breadth, especially the inner 

 pillar, which has sent a process of its foot quite to the habenula 

 perforata. In the middle turn they have grown more than in 

 the apical spire. The inner cell has grown the most, and traces 

 of the head have formed, and the tunnel has made its appear- 

 ance as a narrow split between the cells, about the middle of 

 their length, just above the spiral bundle of nerve fibres. In 

 the basal turn the tunnel is much better developed and the 

 pillars of Corti are nearer their adult condition, for the pillar 

 fibres have appeared in the cells as a clear refractive stripe. 

 The inner hair cells have a different inclination for each turn 

 of the cochlea, and their disposition is shared by the cells of 

 Deiters. Hensen's supporting cells are fewer in the basal turn 

 than in the middle turn, where they are most numerous. The 

 nerves are better developed than in the last stage, they having 

 gained in number and in amount of medullated tissue. The 

 membrana tectoria is as in previous stage. It is connected by 

 the processes from its outer zone with the Deiters cells, and 

 the hairs of the hair cells project freely upward between the 

 processes. The vas spirale is disappearing, while the basilar 

 membrane is growing broader and becoming more like the adult 

 in the character of its fibres. 



