The chief dangers are injury to the contents of the tympanic cavity, such as dislocation or removal of the ossicles; or subsequent meningitis. These mishaps are usually the result of forcible extraction, or of blindly curetting the ear after this has been done. Meningitis, however, has been known to occur, in spite of every precaution being taken, if, owing to caries of the tegmen tympani, the polypus has its origin from the dura mater of the middle fossa. =Prognosis.= If the polypus be single and of recent origin, the result probably of acute inflammation of the middle ear, its removal may cause complete recovery and cessation of the middle-ear suppuration. In the case, however, of multiple polypi associated with chronic middle-ear suppuration and usually signifying underlying bone disease, recurrences may be frequent and further operations may become necessary. It may here be emphasized that a polypus in itself is not a disease, but merely a symptom of disease. After removal of a large polypus, the patient should always be kept under observation for a day or two in case of symptoms of acute inflammation of the mastoid process arising and necessitating further operation. CHAPTER III OPERATIONS UPON THE TYMPANIC MEMBRANE AND WITHIN THE TYMPANIC CAVITY SURGICAL ANATOMY OF THE TYMPANUM =The tympanic membrane.= The chief points to notice when operating on the tympanic membrane are its inclination and its relation to the inner wall of the tympanic cavity. The normal membrane is inclined obliquely downwards and forwards so that it forms an obtuse angle of 140 degrees with the roof and an acute angle of 27 degrees with the floor of the external meatus. In infants the inclination is even greater. Its relation to the tympanic cavity varies in its different parts. It lies nearest to the inner wall in the region of the umbo, being only 2 millimetres distant from the promontory, and is furthest from it in the posterior quadrant. Running backwards, just below the posterior fold, is the chorda tympani nerve, which may be cut through in the act of paracentesis and in division of the posterior fold. =The tympanic cavity.= For the purpose of description the portion of the tympanic cavity above the level of the tympanic membrane is known as the _attic_ or _epitympanic cavity_; whilst the part below its level is called the _cellar_ or _hypotympanic cavity_ (Fig. 186).