THE MIDDLE EAR. 



365 



derived from the auriculo-temporal branch of the trigeminus and from the 

 auricular branch of the pneumogastric, are chiefly medullated and sensory. 

 Sympathetic fibres end in connection with the glands. 



THE MIDDLE EAR. 



The middle ear includes three subdivisions: the tympanic cavity, the 

 Eustachian tube, and the mastoid cells. 



It is an irregular air-chamber, beginning on the lateral wall of the naso- 

 pharynx with the Eustachian tube, which leads upwards, backwards and out- 

 wards, for about one inch and a half into the temporal bone. Opposite the 

 external auditory canal, it widens into the tympanic cavity and continues 

 backwards into the mastoid cells. 



The Tympanic Cavity. The tympanic cavity, also called the tym- 

 panum, is an irregular space within the 'temporal bone, lying between the 



Stapedius 

 muscle 



Internal au- 

 ditory canal 



Tympanic 

 cavity 



Basal turn 

 of cochlea 



FIG. 414. Horizontal section through human middle and internal ear; the malleus is attached to 

 tympanic membrane and the stapes occludes the oval window. X 5/^. (Preparation by Dr. 

 Ralph Butler.) 



internal ear and the external auditory canal. It is lined with mucous mem- 

 brane and contains, in addition to the air which enters by way of the Eusta- 

 chian tube, the chain of ear-ossicles. 



The Membrana Tympani. The tympanic membrane or drum-head 

 is a delicate transparent disk, irregularly oval or ellipsoidal in outline and 

 concave on its outer surface. It is about . 10 mm. thick, except at the 

 periphery, where it is thickened. 



Embedded in the tympanic membrane is the handle of the malleus 

 (Fig. 415), which extends from a point near its middle, upwards and forward? 



