APPLIED ANATOMY. 



for the lower level of the antrum corresponds to the upper edge of the meatus. 

 It is hardly safe to penetrate deeper than 1.5 cm. (fin.) from the meatal spine 

 inward, for fear of wounding the facial nerve. The mastoid antrum lies not only 

 above and posterior to the membrane and tympanic cavity, but extends outward 

 along the posterior and upper portion of the canal, and the facial nerve can be 



Mastoid antrum 



External auditory meatus 



Mastoid cells 



FIG. 108. The mastoid antrum exposed by chiselling through the supratneatal triangle. The mastoid cells exposed 

 by chiselling off the surface of the mastoid process. 



wounded only by passing across the antrum and attacking the bony covering of the 

 Fallopian canal below and anteriorly. 



In doing a tympanomastoid exenteration, a more extensive procedure is 

 performed. It consists in cleaning out the various communicating cavities and 

 throwing them together, thus making their interior more accessible. The antrum is 



reached in one of two ways : either 

 posteriorly, or anteriorly through 

 the meatus. The posterior opera- 

 tion, or that of Schwartze, Zaufal, 

 and others, consists in removing 

 the membranous lining of the bony 

 meatus on its upper and posterior 

 portions down to the tympanic 

 membrane. The antrum is then 

 entered as already described; the 

 posterior bony wall of the meatus 

 is chiselled away, giving access to 

 the tympanum; the ridge of bone 

 separating the roof of the bony 

 meatus from the attic or epitym- 

 panum is chiselled away (see Fig. 

 109), and the membrane and os- 

 sicles removed. This gives access 

 to the tympanic cavity, epitym- 

 panum, and antrum. As much of 

 the mastoid cells as necessary is 

 exposed by chiselling away their external covering of bone even down to the tip of 

 the mastoid process. 



If the anterior operation of Stacke is performed, the membranous lining of the 

 bony meatus is to be loosened arid divided as close to the membrane as possible and 

 drawn forward with the cartilaginous meatus. The drum membrane and as much of 

 the ossicles as possible are then to be removed, and with a chisel or bent gouge the 



FIG. 109. Chiselling away the spur of bone between the roof of the 

 external auditory meatus and attic or epitympanum. 



