462 CLINICAL APPLIED ANATOMY. 



Probably the most frequent seat of arrest is at the junction of 

 the cartilaginous and bony parts of the canal. If syringing fail 

 to remove the intruding substance, instrumental extraction will 

 have to be attempted, and the presence of the membrana tympani 

 at the end of the canal must be borne in mind, otherwise severe 

 damage may be done to it. 



Exostosis of the external auditory meatus usually occurs at 

 the junction of the cartilaginous and osseous portions of the canal. 

 Such a bony outgrowth will have a great tendency to block the 

 meatus, causing retention of secretion and inflammation with 

 deafness. 



Otitis media. The middle ear or tympanum communicates 

 with the outer air through the Eustachian tube. Its mucous 

 membrane is thus brought into direct continuity with that of the 

 naso-pharynx, and a ready path for the passage of micro- 

 organisms provided. Seeing the frequency with which infective 

 conditions are met with about the upper portion of the pharynx, 

 it is remarkable how comparatively seldom the tympanic cavity 

 becomes affected. The action of the cilia of the epithelium of 

 the tube in a direction towards the naso-pharynx, tends to thwart 

 the ascent of bacteria. When infection of the mucous membrane 

 of the Eustachian tube occurs, its lumen is quickly obliterated ; 

 therefore any muco-purulent fluid poured out into the middle 

 ear, when this becomes involved in the ascending inflammation, 

 has no exit. Consequently the membrana tympani is of 

 necessity pressed upon from within, and thereby loses its natural 

 outward concavity, and may even become convex. The fluid in 

 many cases will find its way out through the tympanic membrane 

 by rapid ulceration, seeing that the membrane itself is not more 

 than i of an inch in thickness. As a rule, the perforation 

 takes place in the upper and anterior quadrant, an area which is 

 generally thinner than even the rest of the membrane. It is, 

 therefore, in this region that it is best to perform paracentesis of 

 the cavity. Occasionally the membrana tympani has a natural 

 aperture through it in its upper part, which would then readily 

 give exit to purulent fluid. 



