THE SENSES. 573 



ways, the rods of Corti are seen to consist of tin external and internal 

 pillar, each rising from an expanded foot or base on the basilar mem- 

 brane (o. n. Fig. 388). They slant inwards towards each other, and 

 each ends in a swelling termed the head; the head of the inner pillar 

 overlying that of the outer (Fig. 388). Each pair of pillars forms, as it 

 were, a pointed roof arching over a space, and by a succession of them, 

 a little tunnel is formed. 



It has been estimated that there are about 3,000 of these pairs of pil- 

 lars, in proceeding from the base of the cochlea towards its apex. They 

 are found progressively to increase in length, and become more oblique; 

 in other words the tunnel becomes wider, but diminishes in height as we 

 approach the apex of the cochlea. Leaning, as it were, against these 

 external and internal pillars are certain other cells, of which the exter- 

 nal ones, hair cells, terminate in small hair-like processes. Most of the 

 above details are shown in the accompanying figure (Fig. 388). This 



FIG. 388. Vertical section of the organ of Corti from the dog. 1 to 2, homogeneous layer of the 

 so-called membrana basilaris; u, vestibular layer; v, tympanal layer, with nuclei and protoplasm; 

 a, prolongation of tympanal periosteum of lamina spiralis ossea; c, thickened commencement of 

 the membrana basilaris near the point of perforation of the nerves h d, blood-vessel (vas spirale); 

 e, blood-vessel; /, nerves; </, the epithelium of the sulcus spiralis internus. t, internal or tufted cell, 

 with basil process fc, surrounded with nuclei and protoplasm (of the granular layer), into which the 

 nerve-fibres radiate; Z, hail's of the internal hair-cell; n, base or foot of the inner pillar of organ of 

 Corti; m, head of the same uniting with the corresponding part of an external pillar, whose under 

 half is missing, while the next pillar beyond, o. presents both middle portion and base; r, s, d, three 

 external hair cells; t, bases of two neighboring hair or tufted cells; x, so-called supporting cell of 

 Hensen; w, nerve-fibre terminating in the first of the external hair-cells; II to Z, lamina reticularis. 

 X 800. (Waldeyer.) 



complicated structure rests, as we have seen, upon the basilar membrane, 

 it is roofed in by a remarkable fenestrated membrane or lamina reticu- 

 laris into the fenestras of which the tops of the various rods and cells are 

 received. When viewed from above, the organ of Corti shows a remark- 

 able resemblance to the key-board of a piano. In close relation with the 

 jods of Oorti and the cells inside and outside them, and probably pro- 

 jecting by free ends into the little tunnel containing fluid (roofed in by 

 them), are filaments of the auditory nerve. 



Membranous Labyrinth. This corresponds generally with the 

 form of the osseous labyrinth, so far as regards the vestibule and semicir- 

 cular canals, but is separated from the walls of these parts by fluid (en- 

 dolymph), except where the nerves enter into connection within it. 



