THE NERVOUS SYSTEM. 



,179 



many Insects it is on the wing. Lobsters an(J Crabs have 

 the auditory sacs at the base of the antennae." 



S'lO. 161.— Brain and Auditory Appnrntus of the Cuttle-fish ; a, b, brain ; c, aaditorJ> 

 apparatus ; d, the cavity in which it is lodged ; e,/, 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 Mamtnals) ; 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 (tlie 



Smallest in the body), mal- WKS^^SSlt^ ^>iHi» 



leus, incus, and stapes, ar- 

 ticulated together. The 



cavity communicates with 

 the external air by means 

 of the Eustachian tube, 

 which opens at the back 

 part of the mouth. 3d. 

 The internal ear, or labyri 

 solid part of the temporal 



Fio. 152. — Section of Human Ear; a, external 

 ear, with auditory ciinsil : t, tympanic cavi- 

 ty contaiuing the three bones; c, hummer, 

 and its three muscles, d, e,f; fir, tympanic 

 membrane, or head of the drum ; h, Eusta- 

 chian tube leading to the pharynx ; t, laby- 

 rinth, with semicircular canals and cochlea 

 visible. 



nth, an irregular cavity in the 

 bone, and separated from the 



