122 THE EAR. 



conical shape, rest by their bases upon the basilar membrane, and each one encloses 

 in its substance a cuticular filament which is fixed below to that membrane. This 

 filament is prolonged above in the tapering apex of the cell, between the hair-cells 

 and in close contact with one of them, and is attached above to, or rather expands 

 to form, one of the so-called phalanges of the reticular lamina : it is known as the 

 phalangeal process of Deiters' cell. This cuticular filament may probably be regarded 

 as the equivalent of the rod of Corti, the cell of Deiters to which it belongs being 

 looked upon as representing the protoplasmic cell which lies at the foot of each rod 

 of Corti, and in the young subject encloses the rod. 



Hensen has described a clear oval capsule with a spiral fibre wound around it, occupying 

 the part of the hair-cell next to the free extremity. 



Fig. 139. FOUR CELLS OF DEITERS, FROM THE RABBIT. (Modified 

 from Gr. Retzius.) Highly magnified. 



The phalangeal processes are shown, each expanding to form a 

 phalanx of the reticular lamina. The varicose lines are spirally 

 running nerve-fibrils. 



In most animals there are three series of outer hair- 

 cells, but in man there are four series except in the 

 lowermost turn (fig. 136, ?i) and even five and six in the 

 upper turns of the cochlea (Pritchard) ; but where they 

 are more numerous they tend to be somewhat irregularly 

 placed and intermittent. There are about 12,000 outer 

 hair-cells and 20 hairlets to each cell in the human 

 cochlea (Retzius). The columnar cells outside the hair- 

 cells are much elongated and obliquely disposed, but 



become gradually shorter and more vertical as they pass into the simple cubical 



epithelium on the outer part of the basilar membrane. 



Spaces filled with endolymph are seen both in the inner and outer hair- cell region and 

 communicate between the rods of Corti with the tunnel-space. The largest of these secondary 

 spaces lies between the outer rods and the first row of outer hair-cells (Nuel). (See fig. 136.) 



The cells which immediately succeed the hair-cells form in some animals a distinct 

 swelling or arch outside the hair-cell region, from which and from the basilar membrane they 

 may be separated by a considerable space occupied by endolymph. In the guinea-pig they 

 contain a considerable number of fat globules in the upper turns of the cochlea. They are 

 sometimes known as the (i cells of Hensen," whilst those which follow them and rest on the 

 lateral half of the basilar membrane have been termed " cells of Claudius/' 



Lamina reticularis (figs. 132, 140). The net-like membrane which overlies 

 the outer hair-cell region of the organ of Corti is composed of at least two rows of 

 elongated fiddle-shaped structures termed " phalanges " which are united to one 

 another and to the phalangeal processes of the outer rods in such a manner as to 

 leave between them oblong apertures through which the free ends of the hair-cells 

 with their semicircular rows of auditory hairs project. The phalanges, although 

 they seem like rings, are in reality thin plates with thickened margins, and are to 

 all appearance of a cuticular nature : the most external row of phalanges is in con- 

 tinuity with a cuticular tissue which lies between the external epithelium cells. 

 Attached to the phalanges below are the phalangeal processes of the cells of Deiters 

 (fig. 139). The lamina varies in extent with the number of rows of hair-cells. 

 Where there are four or more of these, a corresponding increase in the number of 

 rows of cells of Deiters and of phalanges is observed. The phalanges serve to 

 isolate the hair-bearing ends of the auditory cells. 



