1366 



SUEFACE AND SUEGICAL ANATOMY. 



curves the lateral is convex forwards, the medial concave forwards. The skin of 

 the osseous portion of the canal is thin and fused with the periosteum, hence 

 when chronically inflamed it is liable to give rise to secondary periostitis and 

 osseous narrowing of the canal. 



The relations of the osseous walls of the canal are of importance to the surgeon. 

 The whole of the upper wall and the upper half of the posterior wall, developed 

 from the squamous portion of the temporal bone, consist of two layers of 



Roof of tympanic antrura 

 Posterior part of middle fossa of skull 



Posterior branch of middle meningeal artery 



Anterior branch of middle meningeal artery 



Portion of cerebellar fossa 



forming posterior wall of 



tympanic antrum 



Interior of transverse sinus 



Anterior limit of transverse sinus 



Tympanic antrum 



Incus 

 Membrana tympani 



Spheno-temporal sinus 

 Trunk of middle meningeal artery 

 Tegmen tympani 

 Chorda tympani nerve 



FIG. 



Head of malleus 

 1070. VIEW OF THE LATERAL WALL OP THE MIDDLE EAR. 



Section through the left temporal bone of a child, to show the relations of the tympanum and tympanic antrum 

 to the middle and posterior fossae of the skull. 



compact bone, a superior and an inferior, which are continuous, the former with the 

 inner table, the latter with the outer table of the skull. The superior plate passes 

 medially to the petro-squamosal suture, where it becomes continuous with the lateral 

 edge of the tegmen tympani, which roofs over the epitympanic recess and the 

 tympanic antrum ; the lower plate bends downwards and medially at its deepest part 

 to form the lower and lateral wall of the recess and the anterior part of the lateral 

 wall of the antrum (Trautmann). It follows, therefore, that when the tympanic 

 antrum is abnormally small, due to sclerosis of the bone, or when it is encroached 

 upon by a far-forward transverse sinus, it, along with the epitympanic recess, can 

 be opened by perforating the junction of the upper and posterior walls of the osseous 

 canal, the instrument being directed medially and slightly upwards. Upon 

 the upper and posterior segment of the external acoustic margin is the supra- 

 meatal spine ; this small but important process, developed from the squamous portion, 



can usually be distinctly 

 made out in the living sub- 

 ject by pressing upwards 

 and backwards with the 

 forefinger placed in the 

 external acoustic meatus. 



The lower half of the 

 posterior wall of the osseous 

 canal (posterior part of the 

 tympanic plate) is fused 



quadrant i SBE^li with the anterior part ol 



the mastoid process, and 

 closes the lower and anterior 

 set of mastoid cells (border 

 cells). 



Anteriorly and inferiorly the osseous canal is related respectively to the 

 mandibular articulation and the parotid gland ; hence it follows that blows upon the 



Membrana flaccida 



Anterior tympano- 

 malleolar fold 



Handle of malleus 



Antero-superior 

 quadrant 



Posterior tympano- 

 malleolar fold 



Lateral process of 

 malleus 

 Long crus of 

 incus 



Postero-superior 

 quadrant 



Postero-inferior 

 quadrant 



Cone of light 



FIG. 1071. LEFT TYMPANIC MEMBRANE (as viewed from the external 

 acoustic meatus). x 3. (From Howden.) 



