TOPOGRAPHICAL ANATOMY OF THE EAR. 



155 



ear is sufficiently simple. The middle ear presents a narrow 

 cavity, Fig. 10, (11), of irregular shape, situated between the 

 external ear and the labyrinth, in the substance of the tem- 

 poral bone. The general arrangement of its parts is shown 

 in Fig. 10. The outer wall of the tympanic cavity is formed 

 by the membrana tympani, Fig. 10, (6). This membrane is 

 concave, its concavity looking outward, and oblique, inclining 

 usually at an angle of about forty-five degrees with the per- 

 pendicular. This angle, however, varies considerably in dif- 

 ferent individuals. The roof is formed by an exceedingly 



FIG, 10. 



General view of the organ of hearing.!, pinna; 2, cavity of the concha, on the walls of 

 which are seen the orifices of a great number of sebaceous glands; 8, external auditory 

 meatus ; 4, angular projection formed by the union of the anterior portion of the concha 

 with the posterior wall of the auditory canal : 5. openings of the ceruminous glands, the 

 most internal of which form a curved line which corresponds with the beginning of the 

 osseous portion of the external meatns; 6. membrana tympani and the elastic fibrous 

 membrane which forms its border ; 7, anterior portion of the incus ; 8, malleus^ v>, 

 handle of the malleus applied to the internal surface of the membrana tympani, which it 

 draws inward toward the projection of the promontory; 10, tensor-tympani muscle, the 

 tendon of which is reflected at a right angle to become attached to the superior portion ot 

 the handle of the malleus; 11. tympanic cavity; 12, Eustachian tube, the internal, or 

 pharyngoal extremity of which has been removed by a section perpendicular to its curve ; 

 13, superior semicircular canal; 14, posterior semicircular canal; 15, external semicircu- 

 lar canal: 16, cochlea; 17, internal auditory canal; IS, facial nerve: 19, large petrosal 

 branch, given off from the ganglioform enlargement of the facial and passing below the 

 cochlea to go to its distribution ; 20, vestibular branch of the auditory nerve ; 21, cochlear 

 branch of the auditory nerve. (SAPPBY, Traite cTanatomie, Paris, 1871, tome iii., p. 808.) 



