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 iu 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 t y mp a mom, 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 
J . ear > w i th auditory canal; 6, tympanic cavi- 
the external air by means ty containing the three bones; c, hammer, 
-c and its three muscles, d, e,f; g, tympanic 
OX tne iliUStacnian tuoe, membrane, or head of the drum; h, Eusta- 
Tjrln’pb nriPTW nt thp haeh chian tube leading to the pharynx; i,laby- 
whicii opens at tne oacx rinth>withsemicircularcanal8andcoch i e a 
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 
