

CHAPTER III. 



Tab. V. — THE HUAfAN ear, and tympanum of the 



ELEPHANT. 



Fig. 1. The organ of hearing; a, the external ear-, b, the meatus^ 

 nnditorius externus, or outward passage of the ear ; leading to c, the 

 membrana tympani, or drum ; d, the ossicula audiius, or little bones 

 of the ear ; e, the semicircular canals ; f, the cochlea ; g, a section of 

 the eustachian tube, which extends from the cavity of the tympa- 

 num, to the back of the mouth or fauces. 



Fig. 2. The bones of the ear magnified, a, the malleus, or mal- 

 let, connected by a process to the tympanum ; the round head is lodged 

 in the body of, b, the incus, or anvil, and the incus is united to, c, the 

 OS orbiculare, or round bone, and this to, d, the stapes, or the stirrup. 

 These bones are named from their shape, and the names assist in con- 

 veying an idea of their form. They are united by ligaments, and form 

 an uninterrupted chain to transmit the vibrations of the atmosphere. 



Fig. 3. The labyrinth, so named from the intricacy of its cavities; 

 it is situated in the petrous part of the temporal bone, and consists of 

 (he vestibule, or central cavity, three semicircular canals, and cochlea^ 

 so named from its resemblance to the windings of a snail shell, and is 

 best explained by the plate, Fig. 1, and 3. 



The vibrations of sounds, striking against the membrana tympani, 

 are propagated by the intervention of these four little bones, to the 

 icater contained within the cavities ol the labyrinth ; and by means 

 of this water the impression is conveyed to the extremities of the au- 

 ditory nerve, and finally to the bra'n. 



Fish require no tympanum, nor external opening to the ear ; the 

 fluid in which they live is the medium for conducting sounds through 

 the bones of the head. 



Fig. 4. The tympanum of the elephant, of its natural size, showing 

 its radiated fibres, supposed to bo muscular. 



