TYMPANIC MEMBRANE 509 



Membrana Tympani. The slope of the tympanic mem- 

 brane has already been referred to. It slopes very obliquely 

 downwards, forwards and medially, and its lateral surface is 

 deeply concave. The deepest point of the concavity is the 

 umbo, 1 which corresponds with the lower end of a bar of bone, 

 the handle of the malleus, which is embedded in the membrane 

 and can be seen through the thin layer of tissue covering 

 it. The handle of the malleus extends upwards, and 

 slightly backwards, from the umbo towards the roof of the 

 meatus ; and a short distance from the upper margin of 

 the membrane it becomes continuous with a small laterally 

 directed process, the lateral process of the malleus, which bulges 

 the membrane towards the meatus. Above the lateral process 

 of the malleus there is a portion of the membrane which is 

 less tense than the remainder. It is the membrana flaccida 

 (ShrapnelPs membrane). It is bounded anteriorly and 

 posteriorly by relatively thickened borders, called the anterior 

 and posterior malleolar folds. The whole of the peripheral 

 margin of the membrane, except that which corresponds with 

 the membrana flaccida, is lodged in a ring-like sulcus of bone, 

 the sulcus tympanicus, which is formed by the tympanic 

 element of the temporal bone. 



Dissection. After the examination of the external meatus 

 is completed the dissector must secure the tensor tympani 

 muscle, which springs from the petrous part of the temporal 

 bone, close to the apex and above the level of the cartilaginous 

 part of the auditory tube. Having secured it, he must trace 

 it laterally, above the auditory tube, to the point where 

 it passes into the bony canal through which it enters the 

 tympanum. Then he must cut away the antero-lateral wall of 

 the cartilaginous part of the auditory tube, from the pharyngeal 

 orifice to the upper -extremity, and pass a probe through the 

 bony part of the tube into the tympanum. He should next turn 

 to the anterior surface of the petrous part of the temporal bone 

 and, with chisel and bone forceps, carefully remove the tegmen 

 tympani and expose the tympanic cavity from above. The 

 dissection must be carried forwards into the auditory tube and 

 backwards into the tympanic antrum. As the dissection is 

 carried forwards a narrow margin of bone must be left along 

 the anterior border of the tympanic membrane, and care must 

 be taken to avoid injury to the tendon of the tensor tympani, 

 which emerges from the extremity of its bony canal, near the 

 medial wall of the tympanum, and crosses the cavity to be 

 inserted into the malleus. The chorda tympani nerve, which 



1 The term " umbo" refers to a prominence and would be more properly 

 used in association with the convexity on the inner side of the membrana 

 tympani than with the concavity on its outer aspect. 



