1148 



THE ORGANS OF SPECIAL SENSE 



angle formed between it and the basilar membrane, is a nucleated mass of proto- 

 plasm; while on the inner side is a row of epithelial cells, the inner hair cells (Fig. 

 856), surmounted by a brush of fine, stiff, hair-like processes. On the inner side 

 of these cells are two or three rows of columnar supporting cells, which are con- 

 tinuous with the cubical cells lining the sulcus spiralis internus. 



The outer rods (Fig. 856), numbering about 4000. also rest by broad foot-plates 

 on the basilar membrane ; they incline upward and inward, and their upper extrem- 

 ity resembles the head and bill of a swan; the back of the head fitting into the 

 concavity the analogue of the sigmoid cavity of one or more of the internal rods, 

 and the bill projecting outward as a phalangeal process of the membrana reticu- 

 laris, presently to be described. 



In the head of these outer rods is an oval portion, where the fibres of which 

 the rod appears to be composed are deficient, and which stains more deeply with 

 carmine than the rest of the rod. At the base of the rod, on its internal side- 

 that is to say, in the angle formed by the rod with the basilar membrane is a 

 similar protoplasmic mass to that found on the outer side of the base of the inner 



FIG 858. Longitudinal section of the cochlea, showing the relations of the scalae, the ganglion spirale 

 fjirale tympani. S.M. Scala media. L.S. Ligamentum spirale G..S. Ganglior 



rod; these masses of protoplasm are probably the undifferentiated portions of the 

 cells from which the rods are developed. External to the outer rod are three or 

 four successive rows of epithelial cells, more elongated than those found on the 

 internal side of the inner rod, but, like them, furnished with minute hairs or cilia. 

 These are termed the outer hair cells, in contradistinction to the inner hair cells 

 above referred to. There are about 12,000 outer hair cells, and about 3500 inner 

 hair cells. 



The hair cells are somewhat oval in shape; their free extremities are on a 

 level with the heads of Corti's rods, and from each some twenty fine hairlets 

 project and are arranged in the form of a crescent, the concavity of which opens 

 inward. The deep ends of the cells are rounded and contain large nuclei; they 

 reach only as far as the middle of Corti's rods, and are in contact with the rami- 

 fications of the nerve filaments. Between the rows of the outer hair cells are 

 rows of supporting cells, called the cells of Deiters; their expanded bases are planted 

 on the basilar membrane, while their opposite ends present a clubbed extremity 

 or phalangeal process. Immediately to the outer side of Deiters' cells are some 



