732 



SPECIAL SENSES. 



clear idea of the structure and relations of the complex anatomical parts in 

 the middle and the internal ear. Such a minute and purely anatomical de- 

 scription would be out of place in this work, where it is desired only to give 

 such an account of the anatomy as will enable the student to comprehend the 

 physiology of the ear, reserving for special description certain of the most 

 important structures. It will be useful, however, to give a general outline of 

 the different parts, with their names. 



The arrangement of the parts constituting the external ear is sufficiently 

 simple. The middle ear presents a narrow cavity (Fig. 263, 11), of irregular 

 shape, situated between the external ear and the labyrinth, in the petrous 

 portion of the temporal bone. The general arrangement of its parts is shown 

 in Fig. 263. The outer wall of the tympanic cavity is formed by the mem- 

 brana tympani (Fig. 263, 6). This membrane is concave, its concavity look- 

 ing outward, and oblique, inclining usually at an angle of forty-five degrees 



with the perpendicu- 

 lar. This angle, how- 

 ever, varies considera- 

 bly in different indi- 

 viduals. The roof is 

 formed by a thin plate 

 of bone. The floor is 

 bony and is much nar- 

 rower than the roof. 

 The inner wall, sepa- 

 rating the tympanic 

 cavity from the laby- 

 rinth, is irregular, pre- 

 senting several small 

 elevations and forami- 

 na. The f enestra ova- 

 lis, an ovoid opening 



FIG. 263. General view of the organ of hearing (Sappey). . , . 



1, pinna ; 2, cavity of the concha, on the walls of which are seen the near "8 Upper portion, 

 orifices of a great number of sebaceous glands ; 3, 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 meatus ; 6, membrana tympani and 



the elastic fibrous membrane which forms its border ; 7, anterior cfafphvfhp hi5P nf 

 portion of the incus ; 8, malleus; 9, handle of the malleus, applied to ^ ' U J LJ 

 the internal surface of the membrana tympani, which it draws in- 

 ward toward the projection of the promontory ; 10, tensor tympani 

 muscle, the tendon of which is reflected at a right angle, to become lip;ament. 

 attached to the superior portion of the handle of the malleus; 11, 6 

 tympanic cavity; 12, Eustachian tube, the internal, or pharyngeal smaller opening the 

 extremity of which has been removed by a section perpendicular to 

 its curve ; 13, superior semicircular canal ; 14, posterior semicircu- 

 lar canal ; 15, external semicircular canal ; 16, cochlea ; 17, internal 

 auditory canal : 18, 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. 



+ +1, _ na x ^-c 

 my ui 



ru ^ TrptiVmlp Tlii i 

 T e * esu lie ' 



HIP 



rifl its 



Below IS a 



f enestra rotunda,which 

 leads to the cochlea. 

 This is closed in the 

 natural state by a 

 In addition the poste- 



membrane called the secondary membrana tympani. 



rior wall presents several small foramina leading to the mastoid cells, which 



cells are lined by a continuation of the mucous membrane of the tympanic 



