586 



THE ORGANS 



membrane is divided into an outer portion, the zona pectinata (Fig. 

 389, i) and an inner portion, the zona tecta (Fig. 389, s). The epithe- 

 lium of the former is of the ordinary columnar type; that of the latter 

 is the highly differentiated neuro-epithelium of Corti's organ. 



The Organ of Corti. — The spiral organ or the organ of Corti (Fig. 

 389, g, and Fig. 390) is a neuro-epithelial structure running the entire 

 length of the cochlear canal with the exception of a short distance at 

 either end. It rests upon the membranous portion of the spiral 

 amina, and consists of a complex arrangement of four different kinds 



limlrns 



mcmiraTia tectorict 



outer hair-cells 



•iierve fibres 



inner rod vas hasUar outer cells of Beitera 

 spiialc Membrane rod 



Fig. 3QO. — Semidiagrammatic Representation of the Organ of Corti and Adjacent 

 Structures (Merkel-Henle.) a, Cells of Hensen; b, cells of Claudius; c, internal spiral 

 sulcus; X, Nuel's space. The nerve fibres (dendrites of cells of the spiral ganglion) are 

 seen passing to Corti's organ through openings (foramina nervosa) in the bony spiral 

 lamina. The black dots represent longitudinally-running branches, one bundle lying 

 to the inner side of the inner pillar, a second just to the outer side of the inner pillar 

 within Corti's tunnel, the third beneath the outer hair cells. 



of epithelial cells. These are known as: (i) pillar cells, (2) hair cells, 

 (3) Deiter's cells, and (4) Hensen's cells (Fig. 390). 



(i) The pillar cells are divided into outer pillar cells and ijiner 

 pillar cells. They are sustentacular in character. Each cell consists 

 of a broad curved protoplasmic base which contains the nucleus, and 

 of a long-drawn-out shaft or pillar which probably represents a highly 

 specialized cuticular formation. The end of the pillar away from the 

 base is known as the head. The head of the outer pillar presents a 

 convexity on its inner side, which fits into a corresponding concavity 

 on the head of the inner pillar, the heads of opposite pillars thus 

 "articulating" with each other. From their articulation the pillars 

 diverge, so that their bases which rest upon the basilar membrane are 



