240 THE ESSENTIALS OF HISTOLOGY 



Corti. They form a single series of columnar cells surmounted by 

 auditory hairs, lying in close apposition to the inner rods. 



The rest of the epithelium -cells have no important characteristics. 

 They are long and columnar next the outer hair-cells, but soon diminish 

 in size, becoming cubical, and in this form they are continued over 

 the outer wall of the cochlear canal. Here they cover a very vascular 

 membrane (stria vascularis, fig. 276, sir), which is frequently pigmented ; 

 its capillary blood-vessels may even penetrate between the epithelium- 

 cells. Internal to the inner hair-cells the epithelium also soon becomes 

 cubical ; it is prolonged in this form over the limbus of the spiral 

 lamina. The epithelium of Eeissner's membrane is of the pavement 

 variety. 



The membrana tectoria (fig. 276, M.t.) is a soft, fibrillated 

 structure, which is attached along the upper surface of the limbus, and 

 lies like a pad over the organ of Corti. It thins out towards the 

 distal margin, here becoming somewhat reticular, and, according to 

 Retzius, attached to the lamina reticularis. In sections it usually 

 appears raised a short distance above the auditory hairs, but it is 

 possible that it may rest upon them during life. 



FIG. 281. GENERAL VIEW OF THE MODE OF DISTRIBUTION OF THE COCHLEAR NERVE, 

 ALL THE OTHER PARTS HAVING BEEN REMOVED. 



The fibres of the cochlear branch of the auditory nerve enter the 

 base of the columella, and run in canals through its substance, being 

 gradually deflected outwards as they pass upwards into the spiral 

 lamina, at the base of which they swell out into a gaiiglionic cord 

 (spiral ganglion). 



After traversing the spiral lamina they emerge in bundles, and the 

 fibres then, having lost their medullary sheath, pass into the epithe- 

 lium of the inner hair-cell region. Here some of them are connected 

 directly with the inner hair-cells, whilst others pass in the form of 

 delicate fibrils across the tunnel of Corti, to become connected with 

 the outer hair-cells (fig. 278). 



