THE NERVOUS SYSTEM. 179 
many Insects it is on the wing. Lobsters and Crabs have 
the auditory sacs at the base of the antennae. 91 
Fig. 151.—Brain and Auditory Apparatus of the Cuttle-fish: a, b, brain; c, auditory 
apparatus; d, the cavity in which it is lodged; e,f ,, g, eyes; 1,2, 3, otoliths. 
A complex organ of hearing, located in the head, exists 
in all Vertebrates, save the very lowest Fishes. As com¬ 
plete in Man, it consists of the following parts: 1st. The 
external ear (which is peculiar to Mammals); the auditory 
canal, about an inch long, lined with hairs and a waxy se¬ 
cretion, and closed at the 
bottom by a membrane, 
called tympanum , or 
“ drum of the ear.” 2d. 
The middle ear, contain¬ 
ing three little bones (the 
smallest in the body), mal¬ 
leus, incus , and stapes , ar¬ 
ticulated together. The 
cavity communicates with Fig. 152.— Section of Human Ear: a, external 
, ear, auditory canal; b, tympanic cavi- 
the external air by means ty containing the three bones; c, hammer, 
r .1 17 ' , 1 and its three muscles, d, e,f; g, tympanic 
01 the Lustachian tube, membrane, or head of the drum; h, Eusta- 
whicll opens at the back chia n tube leading to»the pharynxlaby- 
r rinth, with semicircular canals and cochlea 
part of the mouth. 3d. visible. 
The internal ear, or labyrinth, an irregular cavity in the 
solid part of the temporal bone, and separated from the 
