1876.] Organ of Corti in Mammals. 347 



with the outer rod ; and below the concavity is a little tubercle, from which 

 point the head tapers off to the shaft. The inner surface is continuous 

 with the shaft below, and forms a distinct angle with the upper surface. 

 The sides are marked by a raised curved ridge. 



The head of the outer rod is more rounded, and fits into the concavity 

 of the inner-rod head already mentioned. From its upper part also pro- 

 ceeds outwards a process which is more slender than that of the inner- 

 rod head, and passes further outwards. 



The length of these rods is graduated (as I pointed out in my former 

 paper), and ranges from y^ inch (or *17 inillim.) at the apex of the spiral 

 to ^-J-jy- (or -05 millim.) at its base, where the two rods are of equal length ; 

 but proceeding upwards the outer increase in length much more rapidly 

 than the inner, so that at the apex the former are twice the length of the 

 latter. 



The number of the rods in each row is not the same, there being three 

 of the inner for every two of the outer. According to a careful calcula- 

 tion of mine, there are about 5250 inner and 3500 outer rods in each 

 human cochlea. In substance they resemble delicate hyaline cartilage, 

 show a tendency to split into fibres, and contain no nuclei. 



(2) The Hair-cells are very delicate, columnar in form, with large round 

 nuclei and nucleoli ; the rest of their contents is finely granular. Their 

 summit is flat, and from it project a row of four bristles or cilia ; the rows 

 of bristles run in the direction of the spiral. 



There are four rows of these hair-cells, one situated internal to the rods, 

 and the other three to their outer side. 



The lower ends of the outer hair-cells are evenly rounded oh , and both 

 in man and in the monkey this end is enlarged, giving the cell a flask- 

 shape ; the lower end of the inner hair-cells tapers off, and the whole cell 

 is somewhat larger than the outer ones. The summits of all these cells 

 are attached to the membrana reticularis, and their bristles project through 

 the circular meshes of that membrane. 



(3) The Nuclear Cells, which include those of Claudius, Deiters, and 

 the granular layer of Waldeyer, besides some others scattered about. 



These cells have very distinct nuclei with small nucleoli, and are sur- 

 rounded by some protoplasm, but have no cell-wall ; they are all connected 

 with nerve-filaments. 



These are found : — 1st, on the lower lip of the sulcus internal to the 

 rods, in a mass of three irregular layers (this group has been termed 

 the granular layer by Waldeyer). 2ndly, below the level of the outer hair- 

 cells, and corresponding to them, are found three or four row T s of these 

 nuclear cells, which usually go by the name of the cells of Deiters. 3rdly, 

 there is one of these cells found in each lower angle of the triangular 

 tunnel formed by the sloping rods. Lastly, there are one or two scattered 

 about, which will be considered with the nerves. 



(4) The Supporting Cells of Henseniorm the outer boundary of the organ ; 



2d2 



