558 



COMPARATIVE PHYSIOLOaY. 



The external ear in man being practically immovable, owing 

 to the feeble development of its muscles, has, as compared with 



Ftg. 401. — Section througli auditory organ (after Sappey). 1, pinna; 2, 4, 5, cavity of 

 concha, external and auditory meatus witli opening of ceruminons glands; 6, 

 merabrana tympani; 7, anterior part of incus; 8, malleus;. 9, long handle of mal- 

 leus, attached to internal surface of tympanic membrane — it is here represented as 

 strongly indrawn; 10, tensor tympani muscle; 11, tympanic cavity; 12, Eustachian 

 tube; 13, superior semicircular canal; 14, posterior semicircular canal; 15, exter- 

 nal semicircular canal; 16, cochlea; 17, internal auditory meatus; 18, facial nerve; 

 19, large petrosal nerve; 30, vestibular branch of auditory nerve; 21, cochlear 

 branch of same. 



such animals as the horse or cow, but little use as a collecting 

 organ for the vibrations of the air. The meatus or auditory 

 canal may be regarded both as a conductor of vibrations and 

 as. protective to the middle ear, especially the delicate drum- 

 head, since it is provided with hairs externally in particular, 

 and with glands that secrete a bitter substance of an unctuous 

 nature. 



The llleinbrana Tympani is concavo-convex in form, and 

 having attached to it the chain of bones shortly to be noticed, 

 is well adapted to take up the vibrations communicated to it 

 from the air ; though it also enters into sympathetic vibration 

 when the bones of the head are the medium, as when a tuning- 

 fork is held between the teeth. Ordinary stretched membranes 

 have a fundamental (self-tone, proper tone) tone of their own, 

 to which they respond more readily than to others. 



