Chap, v.] THE EAR. 67 



illary, and obtains its nerve-supply from the auriculo- 

 temporal. 



The tympanum. The width of the tympanic 

 cavity, as measured from its inner to its outer wall, 

 varies from -^th to ^th of an inch. The narrowest 

 part is that between the umbilicus of the membrana 

 and the promontory. A fine rod thrust through the 

 centre of the membrana tympani would hit the pro- 

 montory on the inner wall of the cavity. Above 

 the promontory is the fenestra ovalis, and below and 

 behind it the fenestra rotunda. Skirting the upper 

 and posterior margin of the inner wall of the tympa- 

 num is the aqueduct of Fallopius, containing the 

 facial nerve. The wall of the aqueduct is so thin that 

 inflammatory mischief can readily extend from the 

 middle ear to the facial nerve. The upper wall is 

 very thin, and but little bone separates it from the 

 cranial cavity. The suture between the squamous 

 and petrous bones is found in this wall, and by means 

 of the sutural membrane that separates the bones in 

 the young inflammatory changes may readily spread 

 from the tympanum to the meninges. The floor is very 

 narrow. Its lowest part is below the level of both 

 the membrana tympani and the orifice of the Eusta- 

 chian tube, and hence pus may readily collect in this 

 locality. It is separated by a thin piece of bone from 

 the internal j ugular vein behind, and from the internal 

 carotid artery in front. Fatal haemorrhage from the 

 latter vessel has occurred in connection with destruc- 

 tive changes in this part of the ear. The posterior 

 wall presents the openings of the mastoid cells. 

 These cells are often the seat of suppurative collec- 

 tions, and may be opened by a proper trephine applied 

 to the surface of the mastoid process about half an 

 inch behind the ear. These cellular spaces in the 

 bone are in close relation with the lateral sinus, and 

 thus it happens that thrombosis of the sinus has 



