058 THE EAR. 



Corti. The central part of this apparatus is formed by two sets of 

 stiif, rod-like bodies — the inner and outer ror^.s of (T'or/i (figs. 470,471) — 

 which stand by one end, the foot, ui3on the basilar membrane, the outer 

 series {cr.), at some little distance from the inner (i-r.), and thence are 

 inclined towards each other — the outer series inwards and the inner 

 series outwards — so as to meet by their upper ends or heads, which are 

 thus in contact. In this way each pair of rods forms a sort of arch with 

 slanting sides (fig. 471), and since both inner and outer rods- are, 

 respectively, in lateral juxtaposition, the double series of inclined 

 columns forms a tunnel (fig. 470) along the whole extent of the basilar 

 membrane, which in the natural condition is filled with endolymph. 



On the inner side of the inner rods is a row of epithelial cells — inner 

 hair-cells — which are surmounted by a brush of fine, short, stiff hairlets, 

 and external to the outer rods are three or four successive rows of 

 similar but more elongated cells — outer hair-cells — which are mclined 

 in a direction more or less parallel with that of the corresponding series 

 of rods. The hairlets of these outer hair-cells project through rings 

 (fig. 470, m, n, o), which surround the tops of the cells, and which are 

 bounded by minute, fiddle-shaped cuticular structures — the so-called 

 lihalamjes — connected both to one another and to the heads of the outer 

 rods. A reticular lamina (fig. 470, l.r.) is thus formed which covers this 

 part of the organ of Corti, like a wire net. 



On either side of the two sets of hair-cells the epithelium, becoming 

 gradually shorter, passes continuously into the simple layer of cubical 

 cells which is found both in the spiral groove and also covering the 

 outermost part of the basilar membrane. 



The whole organ is, in addition to the reticular lamina, covered by a 

 comparatively thick, fibrillated, and, to all appearance, highly elastic 

 membrane — the tectorial memlmme (fig. 469, 31. t.) — which is attached 

 by one edge to the upper surface of the limbus, falls over the crest of 

 the latter and rests by the other edge and by the adjoining part of its 

 under surface on the rods of Corti and the hair-cells, converting in 

 this way the spiral groove into a canal. It will be necessary to describe 

 more minutely these several parts of the organ of Corti. 



Rods of Corti. — The inner and outer rods of Corti differ considerably 

 from one another in size and shape, although agreeing, for the most 

 part, as regards the details of their structure. Each inner rod may be 

 best compared in shape to a human ulna, the upper end of the rod being 

 pretty accurately represented by the head of that bone, the olecranon 

 and coronoid processes, as well as the concave articular surface between, 

 being readily recognisable. The outer rods, on the other hand, some- 

 what resemble in shape a swan's head and neck ; the rounded part, 

 which represents the back of the head, fitting into, and being connected 

 with, the concave surface on the head of the con-esponding inner rod 

 (or rather of two or three inner rods, for the latter are smaller and 

 more numerous than the outer ones), while the part which represents 

 the bill projects outwards and becomes connected with the phalanges 

 of the lamina reticularis, aiding to form the first series of rings for the 

 hair-cells. Both inner and outer rods are more slender about the middle 

 of their length and expand again below, so as to rest upon the basilar 

 membrane by a somewhat widened foot. Both are distinctly striated 

 throughout their length (fig. 474), and the striation or fibrillation, as is 

 particularly well seen in the outer rods, passes, at the point of attach- 



