78 SURGICAL APPLIED ANATOMY. [Chap. v. 



behind it the fenestra rotunda. Skirting the upper 

 and posterior margin of the inner wall of the tympa- 

 num is the aqueduct of Fallopius, containing the 

 facial nerve. The wall of the aqueduct is so thin that 

 inflammatory mischief can readily extend from the 

 middle ear to the facial nerve. The upper wall is 

 very thin, and but little bone separates it from the 

 cranial cavity. The suture between the squamous 

 and petrous bones is found in this wall, and by means 

 of the sutural membrane that separates the bones in 

 the young inflammatory changes may readily spread 

 from the tympanum to the meninges. This petro- 

 squamous suture is generally obliterated by the end of 

 the first year (Symington). The floor is very narrow. 

 Its lowest part is below the level of both the rnern- 

 brana tympani and the orifice of the Eustachian tube, 

 and hence pus may readily collect in this locality. It 

 is separated by a thin piece of bone from the internal 

 jugular vein behind, and from the internal carotid 

 artery in front. Fatal haemorrhage from the latter 

 vessel has occurred in connection with destructive 

 changes in this part of the ear. The posterior wall 

 presents the openings of the mastoid cells. 



The mastoid cells are often the seat of sup- 

 purative collections, due to the spreading of inflamma- 

 tion from the tympanum. The implication of these 

 spaces forms one of the most important complications 

 of middle ear disease. In the infant the mastoid as 

 a distinct process has no existence, but in the mastoid 

 segment of the petrous bone is a single air cell, the 

 mastoid anlruni, which communicates by a large 

 opening with the posterior part of the upper portion 

 of the tympanum above the membrana. The roof of 

 this cell is quite close to the cranial cavity, while its 

 outer wall is' very thin, about 2 mm. in thickness. 

 From the latter fact it happens that in infants pus in 

 the antrum can very readily reach the surface, or be 



