DEVELOPMENT OF THE ORGAN OF CORTI 309 



SUMMARY 



1. The tunnel space is developed around the spiral nerve 

 bundle, which runs between the nucleated portions of the inner 

 and outer pillar cells. It is originally an intercellular cleft, the 

 fluid contents of which are elaborated in the vacuolated cyto- 

 plasm of the pillar cells and discharged into the adjoining space. 

 Parts of this secreting protoplasm undergo a process of cytolysis 

 or liquefaction, so that the cleft enlarges and the fluid contents 

 increase in quantity at their expense. 



2. The tunnel extends upward along the vacuolated zones of 

 the intermediate portions of the pillars. This clear cytoplasm 

 also disappears by a similar process of secretion and cytolysis. 

 Ultimately the intermediate segments of the pillars become 

 transfonned into pillar bodies, reduced almost to their fibrillar 

 apparatus of support, the outer being represented by thin 

 cyhndrical strands which are separated by large intercellular 

 clefts, and the inner, lamellar in shape, being composed of a 

 medial, thin, fibrillar lamella and a lateral narrow zone of clear 

 cytoplasm. 



3. In the earhest stage of development the heads of the outer 

 rods of Corti are represented by thin tapering segments, nearly 

 as long as the neighboring outer hair cells. They are character- 

 ized by the presence of two fibrillated bundles, the intracephalic 

 rootlets of the fibrils of the phalanx process and the apical intra- 

 cephalic extremities of those of the future pillar body. More- 

 over, pecuhar structures, a more homogeneous cytoplasm and a 

 system of obturator septa between the two rows of the future 

 outer and inner heads and between the contiguous surfaces of 

 the heads of each row, constitute important features, which 

 enable one to recognize the *nature of these apical segments. 



4. In a more advanced stage the long superficial segment of 

 the outer pillar enlarges rapidly into a shorter prismatic mass, 

 the head proper, within which develop, in contact with the 

 obturator septa, a firmer exoplasmic collar, and ulthnately a 

 head cap, enclosing imperfectly a clearer endoplasmic mass, 

 which is traversed by the nearly horizontal and the vertical 



