518 STUDIES IN ADVANCED PHYSIOLOGY. 



organs of Corti and the endings of the nerves and so the 

 points in the ear where physical vibrations give rise to 

 nervous sensations. 



THE HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 



1. Sacculus and Utriciilus. Both sacculus and utricu- 

 his are hollow, sac-like structures rilled with endolymph. 

 There is found, however, at those points on the sacculus 

 and utriculus where the auditory nerve enters them a small 

 projection called the maciila acustica. This macula acustica 

 is a kind of a projection inward, on the top of which there 

 are the auditory hairs projecting into the endolymph. These 

 auditory hairs are really continuations of the auditory cells 

 which are found in the macula acustica and which are con- 

 nected at their bases directly with the auditory nerve. 



In the mucilaginous matrix between these auditory cells 

 there are imbedded very small stones called the otoliths. 

 These otoliths are composed of calcium carbonate and their 

 function is probably to help stimulate the nerve cells by 

 their inertia when set in motion by the endolymph. The 

 otoliths in man are only microscopic crystals, but in the 

 fishes and some of the invertebrates they become quite large, 

 a half inch or more in diameter. 



2. Semicircular Canals. Connected with the utriculus 

 are three semicircular canals each of which possesses on 

 one of its limbs an enlargement known as the ampulla. A 

 cross-section of such an ampulla shows, projecting into the 

 interior of it the crista acustica. This projects inward 

 relatively much further than the macula acustica just re- 

 ferred to. 



An epithelium of auditory cells connected with the audi- 

 tory nerve covers the crista. Delicate hairs from these pro- 

 ject into the surrounding endolymph. At other portions of 

 the semicircular canal it is a smooth tube lined with ordi- 

 nary epithelium, and has at these portions probably no definite 

 sensory functions. 



