cha P .v.] THE EAR. 77 



rapidly. The membrane has been ruptured during 

 fits of sneezing, coughing, vomiting, etc. The same 

 lesion has followed a box on the ear, and even simple 

 concussion such as that produced by a loud report 



The umbo, or deepest point of the depression in 

 the diaphragm, is just below the centre of the entire 

 membrane, and corresponds to the attachment of the 

 end of the handle of the malleus. The rest of the 

 handle can be seen through the membrane during life. 

 The head of the malleus is in no connection with the 

 membrane, being above its highest limits. The seg- 

 ment of the membrane above the umbo is very freely 

 supplied by vessels and nerves ; it corresponds to the 

 handle of the malleus, and to the chain of ossicles, and 

 is opposite to the promontory and the two fenestrse. 

 The chorda tympani nerve also runs across this supra- 

 umbilical portion. The segment below the umbo, on 

 the other hand, corresponds to no very important 

 parts, and is less vascular and less sensitive. Para- 

 centesis of the tympanum through the membrana 

 tympani should therefore always be performed in the 

 subumbilical segment. If performed above the umbo 

 the knife may strike the incus and loosen that bone 

 from its frail attachments. The malleus and stapes 

 are too firmly attached to be readily separated. 



The membrane is supplied by the stylo-mastoid 

 artery, and the tympanic branch of the internal max- 

 illary, and obtains its nerve supply from the auriculo- 

 teinporal. 



The tympanum. The width of the tympanic 

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

 varies from T \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 



