THE AUDITORY APPARATUS 



of the incisura tympanica, and thus map out the membrana flaccida. The 

 long crus of the incus can be faintly seen through the membrana tympani, 

 parallel with and posterior to the handle of the malleus. 



Antrum Tympanicum. The tympanic antrum is a recess 

 or air-chamber, in the temporal bone. It lies immediately 

 behind the epitympanic portion of the tympanic cavity and, 

 in the adult, it is 14 mm. (about half an inch] from the 

 surface of the skull, medial to the suprameatal triangle. In 

 the child it is much more superficial. 



The cavity of the tympanic antrum is lined with mucous 

 membrane which is continuous, 

 anteriorly, through a relatively 

 wide aperture called the adittts, 

 with the mucous membrane of 

 the tympanic cavity, and it is 

 6 also continuous, posteriorly and 

 below, with the mucous mem- 

 brane of the air-cells in the 

 mastoid portion of the temporal 

 bone. 



The roof of the tympanic 

 antrum is formed by a thin plate 

 of the petrous part of the tem- 

 poral bone, called the tegmen 

 FIG. 214. Left Malleus and Incus. * 



(After Heimhoitz. ) tympani. It separates the tym- 



1. Tendon of tensor tympani. panic antrum from the cavity of 



2. Handle of the malleus. tVp mirlr11<a -Friccn r\f tVip> clrnll 



3. Long crus of the incus. tnG Diddle lOSSa Ol the SkUll 



4 . Short crus of the incus. and from the membranes cover- 

 s' Incus. . . . 



6. Anterior process of the malleus. The ing the inferior Surface OI the 



ne The "two" ^ th" temporal lobe of the brain. The 

 of the lateral wall is formed by that 



portion of the squamous part 



of the temporal bone which lies immediately above and 

 behind the aperture of the external acoustic meatus. The 

 posterior wall and \ktfloor are formed by the mastoid portion 

 of the temporal bone, and it is through apertures in those 

 boundaries that the cavity of the tympanic antrum communi- 

 cates with the mastoid air-cells. On the medial wall^ which 

 is formed by the petrous part of the temporal bone, is a 

 horizontal bulging, caused by the lateral semicircular canal 

 of the internal ear ; the bulging extends forwards into the 

 aditus (Fig. 205). Immediately anterior to the medial margin 



