DIAGRAM OF THE HUMAN EAR. (After Hesse and Weber.) 



A, the outer ear-passage; B, the middle ear; C, the bone (periotic) enclosing the inner ear. 



i. The ear-trumpet or pinna, practically fixed in man and unimportant. In many mammals it helps to locate the sound. 2. The 

 outer ear-passage with the drum or tympanum (3) running across its inner end. The drum vibrates when sound-waves strike it. 

 4, 5, 6. The ear-ossicles, hammer (malleus), anvil (incus), and stirrup (stapes), which by their movements transmit the vibra- 

 tions from the drum to the inner ear. The "window" in the bony wall of the inner ear on which it abuts is called the fenestra 

 ovalis. 7. The Eustachian tube, leading down to the back of the mouth; by it air can enter indirectly into the middle ear. 8. 

 The larger chamber of the inner ear, called the utriculus, with three semicircular canals arising from it. They have to do with 

 balancing and the like. 9. The smaller chamber or sacculus connected with the coiled cochlea, the essential organ of hearing 

 (10), containing the organ of Corti. There is also shown the endolymphatic duct (12). u. Another "window" in the periotic 

 bone, the fenestra rotunda. The dark-coloured cavity is called the perilymph-space; it contains a fluid called perilymph; it is 

 separated from the internal cavity of the ear by a membrane, within which there is endolymph. The dotted tissue is bone. 



