

SPIKAL OEGAN OF COKTI. 851 



i outer rod. The expanded bases of the inner rods are situated on the innermost portion 

 of the membrana basilaris, immediately to the outer side of the foramina nervosa of the 

 labium tympanicum. The intermediate parts of the inner rods are sinuously curved, and 



. form with the membrana basilaris, an angle of about 60. The outer rods number about 

 4000, and are longer than the inner, especially in the upper part of the cochlea. They are 



! more inclined towards the membrana basilaris, and form with it an angle of about 40. The 

 head of each is convex internally, to fit the concavity on the head of the inner rod, and is pro- 



' longed outwards as a plate, the phalangeal process, which becomes connected with the lamina 

 reticularis ; in the head is an oval body which has an affinity for certain reagents. The 

 main part of each rod consists of a nearly homogeneous material, which is finely striated. 

 At the bases of the rods, on the side next Corti's tunnel, is a nucleated mass of protoplasm 

 which reaches as far as the heads of the rods, and covers also the greater part of the 

 tunnel floor ; this protoplasm may be regarded as the undifferentiated part of the cell from 

 which the rod was developed. Slit-like intervals, for the transmission of nerves, exist 

 between the intermediate portions of adjacent rods. 



Hair Cells. These, like Corti's rods, form two sets, inner and outer. The former 



i consists of a single row lying immediately internal to the inner rods the latter of three, 

 or, it may be, four rows placed to the outer side of the external rods. The inner hair 

 cells are about 3500 in number ; the diameter of each is greater than that of an inner 

 rod, and so each inner hair cell is supported by more than one rod. Somewhat oval in 

 shape, their free extremities are surmounted by about twenty fine hair-like processes, 

 arranged in the form of a crescent, with its concavity directed inwards. The deep end 

 of the cell contains a large nucleus and is rounded ; it reaches only about half-way 

 down the rod, and is in contact with the arborisations of the nerve terminations. To 

 the inner side of this row of hair cells are two or three rows of elongated columnar cells, 

 which act as supporting cells, and are continuous with the low columnar cells lining the 

 sulcus spiralis internus. The outer hair cells number about 12,000, and form three 

 rows in the basal coil and four rows in the upper two coils, although in the higher 

 coils the rows are not so regularly arranged. The rounded free ends of the hair cells 

 support some twenty hairlets arranged in the form of a crescent, opening inwards. Their 

 deep extremities reach about half-way to the membrana basilaris, and are in contact with 

 the nerve arborisations. 



Alternating with the rows of the outer hair cells are the rows of Deiters' supporting 

 cells, the lower extremities of which are expanded on the membrana basilaris, whilst their 

 upper ends are tapered ; the nucleus is placed near the middle of each cell, and, in addition, 

 each cell contains a bright, thread-like structure called the supporting fibre. This fibre 

 is attached by a club-shaped base to the membrana basilaris, and expands, at the free 

 end of the cell, to form a phalangeal process of the membrana reticularis. 



The cells of Hensen, or outer supporting cells, consist of about half a dozen rows, 

 immediately outside Deiters' cells, and form a well-marked elevation on the floor of the 

 ductus cochlearis. Their deep extremities are narrow and attached to the membrana 

 basilaris, while their free ends are expanded ; each cell contains a distinct nucleus and 

 some pigment granules. The columnar cells, situated externally to the cells of Hensen, 

 cover the outer part of the zona pectinata, and are named the cells of Claudius. A space, 

 the space of Nuel, exists between the outer rods of Corti and the neighbouring row of 

 hair cells ; it communicates internally with Corti's tunnel, and extends outwards between 

 the outer hair cells as far as Hensen's cells. 



The lamina reticularis is a thin cuticular structure which lies over the organon 

 spirale, and extends from the heads of the outer rods as far as Hensen's cells, where it 

 ends in a row of quadrilateral areas which form its outer border. It consists of two or 

 three rows of structures, named phalanges, which are elongated cuticular plates resembling 

 in shape the digital phalanges. The innermost row is formed by the phalangeal processes 

 of the heads of the outer row of Corti's rods ; the succeeding row, or rows, represent the 

 expanded upper ends of Deiters' supporting cells. The number of rows of phalanges, 

 therefore, varies with the number of rows of outer hair cells and the alternating cells of 



i Deiters. The free ends of the hair cells occupy the somewhat circular apertures between 



, the constricted middle portions of the phalanges. 



The membrana tectoria (Fig. 725) is an elastic membrane overlying the sulcus spiralis 

 nternus and the organon spirale. Attached, by its inner end, to the limbus laminse 

 spiralis, near the lower edge of the membrana vestibularis, it reaches outwards as far as 

 the outer row of hair cells. Its inner portion is thin and overlies the auditory teeth of 

 Huschke. Its outer part is thickened, but becomes attenuated near its external border, 

 which, according to Retzius, is attached to the outer row of Deiters' cells. Its lower edge 



