EXTERNAL STRUCTURE. 



78 



delicate membrane, with several apertures or holes, h, f, k, the principal 

 of which we shall describe. 



STRUCTURE OF THE EAR 



EXPLANATION OF THE PRINCIPAL PARTS, 



WITH THKIE ANATOMICAL TERMS. 



a Meatus extermts, or outer passage. 



b Memhrana tympani, or membrane stretched over the entrance to the drum of tl»« 

 ear. 



c Malleus, or hammer, the first of the ossicuM (little bones), and resting' upon the 

 membrana tympani. 



d Incus, or anvil. 



e Orbiculare, or round bone. 



X Stapes, or stirrup bone, resting" on the membrane which covers the Jhramcn ovale, 

 or oval window, and which conducts to the labyrinth of the ear. 



g One of the muscles of the tympanum attached to the stapes. 



h Vestibule or hall, the first portion of the labyrinth of the ear. 



t Semicircular canals. 



k Openinsrs into the canals. 



/ 'Tympanum, or drum of the ear. 



in Cochlea, or shell-like portion of the labyrinth. 



n Meatus auditoHus internus, or internal passapfe, through which both divisions of the 

 seventh pair of nerves enter the ear. At the end of it is the cribriform sieve- 

 like plate, through which the portio mollis, or soft portion of the seventh pair of 

 nerves, and which is the auditory nerve, or nerve of hearing, enters to spread over 

 the cochlea and vestibule. 



Eustachian tube, or communication between the tympanum and the mouth, so called 

 from its discoverer. 



p Cord, or nerve of the ear, corda tympani, a branch of the portio dura, hard portion, of 

 the seventh pair of nerves, united to a portion of the fifth pair, running across the 

 tympanum, and ramifying on it and on the membrane. 



J Exit of the portio dura from the temporal bone, to spread over the face. 



