150 On the Structure and Function of the Rods 



III. — On the Structure and Function of the Rods of the Cochlea 

 in Man and other Mammals. By Ukban Pritchard, M.D., 

 F.R.C.S., Demonstrator of Physiology, King's College, London. 

 {Bead before the Medical Microscopical Society, Feb. 21, 1873.) 

 Plate XIII. 



Before entering upon the description of the rods themselves, it may 

 be well to refer briefly to the mechanism of the ear, and the method 

 by which we are able to hear and distinguish certain sounds. 



The ear itself, as is well known, is one of the most complicated 

 organs of the body, consisting of the external, middle, and internal 

 sections : the two former are merely concerned in collecting and 

 conducting sounds or vibrations ; while the duty of the internal 

 portion consists in receiving, localizing, and, moreover, clearly dis- 

 tinguishing them. Now, it is simply with this last and most 

 delicate function of the organ that I purpose to deal, my aim being 

 to describe the true construction and use of the cochlea so far as its 

 task of distinguishing the various sounds is concerned. 



I may state that, for convenience sake, I shall in the course of 

 my remarks speak of the cochlea with its apex uppermost. This 

 cochlea, it must be borne in mind, consists of a spiral canal, in form 

 and shape very similar to the inside of a snail-shell. From the axis, 

 or modiolus as it is called, of this spiral, there proceeds horizontally 

 a plate of bone, the lamina spiralis, which almost divides this canal 

 into two. From this plate again there extend two membranes to 

 the walls of the canal, thus separating it into three minor canals. 



Of these two membranes the upper one or membrane of Reissner 

 (Fig. II.) arises just behind the teeth of the limbus (as the peripheral 

 end of the bony lamina is called), and passes upwards and outwards 

 to the upper part of the ligament of the cochlea ; it is exceedingly 

 delicate, and is composed of a single layer of flattened nucleated 

 cells, closely adhering to each other, and which are situated on a 

 very thin membrane. 



EXPLANATION OF PLATE XIII. 



Fig. I. — The upper extremities of the roils (dog), showing the mode of articula- 

 tion and processes. Drawn by camera, x 500 diam. ; i, inner rod ; o, outer 

 rod. 

 „ II.— A diagramatic drawing of a vertical section of the central canal of the 

 cochlea, x about 150 diam. 1. Scala vestibuli. 2. Central canal of 

 cochlea. 3. Scala tympani. A, Membrane of Reissner ; B, Membrana 

 tectoria ; C, Bony lamina spiralis ; D, Membrana basilaris ; E, Liga- 

 ment of cochlea ; F, Nerve plexus ; G, Epithelium ; H, Membrana 

 reticularis ; L, various cells ; i, inner rod ; o, outer rod. 

 ,, III. — Three pairs of rods carefully drawn from three sections of the cochleae of 

 the same animal (cat), showing the mode of graduation — 1, from near 

 the apex of cochlea ; 2, from about the middle ; 3, from near the base, 

 X about 250 diam. ; i, inner rod ; o, outer rod. 



