THE EAR AND HEARING. 



563 



against one another by their upper ends so as to cover in a 

 tunnel; they are known respectively as the inner and outer 

 rods, the former being nearer the lamina spiralis. Each 

 has a somewhat dilated base, firmly fixed to the basilar mem- 

 brane; an expanded head where it meets its fellow (the inner 

 rod presenting there a concavity into which the rounded 

 head of the outer fits); and a slender shaft uniting the two, 

 slightly curved like an italic /. The inner rods are more 

 slender and more numerous than the outer, the numbers 

 being about 6000 and 4500 respectively. Attached to the 

 external sides of the head of the outer rods is the reticular 

 membrane (r, Fig. 167), which is stiff and perforated by 

 holes. External to the outer rods come four rows of outer 

 hair-cells, connected like the inner row with nerve-fibres; 

 their bristles project into the holes of the reticular mem- 

 brane. Beyond the outer hair-cells is ordinary columnar 

 epithelium, which passes gradually into cuboidal cells lining 

 most of the membranous cochlea. The upper lip of the 

 sulcus spiralis is uncovered by epithelium, and is known as 

 the Iwibus lamince spiralis; from it projects the tectorial 

 membrane (t, Fig. 166) which extends over the rods of Corti 

 and the hair-cells. 



Nerve-Endings in the Semicircular Canals and the 

 Vestibule. Medullated fibres (/, Fig. 168) from the vestib- 

 ular branch of the auditory nerve are distributed along a line 

 across the ampulla of each 

 semicircular canal. They lose 

 their medullary sheath close 

 to the basement membrane, 

 a, which the axis cylinders 

 pierce. The axis cylinders 

 branch among the epithelium 

 cells, which at this place are 

 several rows thick, but have 

 not yet been traced into direct b- 

 continuity with any of them. 

 The cells of the epithelium 

 are of two varieties. The 

 columnar cells or hair cells, c, 

 do not reach the 

 membrane, are 

 slightly granular : from the free end of each projects a rigid 



FIG. 168. Diagram of epithelium in 

 basement nervous region of ampulla of a semicir- 

 cular canal. 



nucleated or 



