45 Anatomy Applied to Medicine and Smgery. 



by directing the patient to swallow a mouthful of water, 

 and at the same time forcing air into the nasal passages 

 by means of the air-bag, the orifice of the tube being open- 

 ed by the act of swallowing, the compressed air enters 

 the middle ear. 



Operations. For mastoiditis. In this, the opera- 

 tion is performed by making an incision about a quarter 

 of an inch behind the insertion of the auricle, extending 

 from the posterior root of the zygoma, above, to the tip of 

 the mastoid, below. The opening through the mastoid 

 processs should be made within McEwen's "supra-meatal 

 trliangle." This triangle is bounded above by the ptos- 

 terior root of the zygoma, which, together with the upper 

 and the posterior margins of the bony meatus, forms the 

 apex, while an imaginary line joining the ends of these 

 sides forms the base of the triangle. The opening in the 

 bone should be in a direction, forwards and inwards, since, 

 if it were made directly inwards, the sigmoid sinus might 

 be opened. Parac en tests of the membrana tympani is 

 best performed through the lower portion of the mem- 

 brane, since, if it were done above the umbo, there would 

 be danger of injuring the ossicles, or the chorda tympani 

 nerve as it crosses this membrane. 



