542 



THE HUMAN BODY. 



Fig. 148), which is stiff and perforated by holes. Exter- 

 nal 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 membrane. 

 Beyond the outer hair-cells is ordinary columnar epithe- 

 lium, 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. 147) which extends over 

 the rods of Corti and the hair- 

 cells. 



Nerve-Endings in the Semicir- 

 cular Canals and the Vestibule. 

 Nerves reach the ampulla of each 

 semicircular canal, and, perforat- 

 ing its wall, enter the epithelium 

 lining it, which is there made of 

 cells of two kinds (Fig. 149). 

 Some of the cells are colum- 

 nar (c), and each of these bears 

 FIG. HO. sensory epithelium on its free end a long stiff hair 

 o r a nai,r<i > s u a! : a cuie ( . semicircular (*) A branch of a nerve fibre 



(n) joins the other end of the 



cell. Between the columnar cells are more slender, stiffer 

 nucleated supporting cells (/). The hairs of the colum- 

 nar hair-cells are quite long, several times longer than the? 

 cells. They do not project freely into the endolymph 

 which fills the semicircular canals, but are imbedded in a 

 mucus-like substance, somewhat dome-shaped, known as 

 the cupula terminal-is, which is not represented in the 

 figure. In the utricle and saccule are somewhat similar 

 structures; but collected among the hairs, and imbedded 

 in gelatinous matter, are minute calcareous particles, the 

 ear-stones or otoliths. 



The Loudness, Pitch, and Timbre of Sounds. Sounds, 

 as sensations, fall into two groups notes and noises. Physi- 



