77//1 MIDDLE KM! 10.-,:; 



plica"', the pars flaccida, or Shrapnell's membrane, is thin and flaccid, and is attached 

 directly to the petrous hone in the tympanic notch tnotch of Uivimis). The larger 

 ji.irt of the tympanic menihraiie. the pars tensa, is inferior to the plica' and is tightly 

 stretched. Its thickened margin, the limbus, is attached by a fihro-cart ilaiimnus 

 annulus to the tympanic sulcus, and at the spines uf tlie tympanic ring is continuous 

 with the plica'. 



Structure of the tympanic membrane. The tympanic membrane is about 1 mm. 

 thick, and consists of four layers. The lateral cutaneous layer is very thick, 

 and is a continuation of the cutaneous layer of the external acoustic meatus. Next 

 to it is a radiate fibrous layer, composed of connective tissue, the fibres of which 

 are attached to the nianubrium of the malleus and radiate from it. The circular 

 fibrous layer, which has its fibres arranged concentrically and is especially thick at the 

 circumference, is closely bound to the radiate layer, and. finally, the mucous layer, 

 which is a continuation of the mueosa of the tympanic cavity, covers the medial 

 surface of the membrane smoothly, except where the nianubrium of the malleus 

 causes a projection. The fibrous layers are attached to the fibre-cartilaginous ring 

 and are lacking in the pars flaccida. 



The tympanic cavity is an air-space lined with mucous membrane and situated 

 between the external and internal ears dig. 747). It measures about 15 mm. in 

 both ventro-dorsal and vertical directions, and it.- width varies from 2 nun. to I mm. 

 or more, being narrowest at the centre and wider superiorly than inferiorly. It pre- 



Fio. 748. LATERAL Sriu-\\< -K OF TUB I. KIT M I:\IHKANA TVMPANI. (Enlarged from life.) 



Pars flaccida or ShrapneU'a membrane Posterior plica 



Anterior plica jjf\ ?VH 



'_ 



MAILEOLAR PROMINENCE CAUSED BY 

 LATERAL PROCESS OF MALLE 



-Pars lenaa of tympanic 



UNBO, CORRESPONDS TO TIP OF- 111 ^^ ' 

 MANUBBIUM OF MALLEUS 



Cone of light 



sents for examination six walls, each of which is named from the principal structure 

 which is in relation with it and also from its position. These walls have been par- 

 tially described in connection with the temporal bone (pp. 66, 67), so that it will be 

 necessary here merely to name the various parts. 



The tegmental (superior) wall is roofed by the thin legmen ti/inptnri (fig. 751). 

 At its lateral ed.se. in the infant, is the petro-squamous suture, and in this situation 

 an occasional slight deficiency of the roof may persist. The jugular wall or floor 

 separates the cavity from the jugular fossa, and presents a prominence corre- 

 sponding to the base of the styloid process, and numerous depressions. Upon 

 the mastoid (posterior) wall may be noted inferiorly. additional tympanic crllulir 

 (fig. 749), and above these is the pi/nn/iidn/ n/n'm //<r with the tendon oj tin ,*//;- 

 pnlius muscle emerging from its apex, and superiorly the chorda tympani nerve, 

 issuing from its canal. Superior to these are a depression, the postmar sinus, a 

 fossa, which marks the attachment of the posterior ligament of the incus, and the 

 opening into the tympanic (mastoid) antrum. The tiitujxniir (mustafit) untrum leads 

 posteriorly and inferiorly into the tmutotid atr-eeQt, which are described on pp.61, 

 65. 67, and anteriorly connects with the superior part of the tympanic cavity, 

 epitympamc rrrrss, or attic (fig. 751 ). which extends inferiorly to the level of the tym- 

 panic membrane and superiorly to the tegmen tympani. The prominence of the 

 facial (I''iil/oj>i<ni) ciintil and the promincncr oj thr Intiral semicircular canal are seen 

 superiorly, partly upon the posterior, but mainly upon the medial wall. The car- 



