THE NERVOUS SYSTEM. 179 



many Insects it is on the wing. Lobsters and Crabs have 

 the auditory sacs at the base of the antennae." 



Fia. 151. Brain and Auditory Apparatus of the Cuttle-fish: a, b, brain ; e, 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 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 



... enr, with auditory caual ; b, tympanic cavi- 



tlie external ail' by means ty containing the three bones ; c, hammer, 



of the Eustachian tube, 



which opens at the back 



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 



