SURGICAL ANATOMY OF THE CRANIUM. 21 



passage is formed by a tubular prolongation inwards of 

 the cartilage of the external ear, which, however, is not 

 complete at the upper part; and its inner two-thirds by 

 the canal in the temporal bone. There are several small 

 fissures in the cartilaginous part, which are sometimes 

 very wide apart a circumstance explaining the passage 

 of pus into the meatus, from abscesses which have formed 

 external to it. In length the meatus is about an inch 

 and two or three lines ; but owing to the obliquity of the 

 attachment of the membrana tympani, its anterior wall 

 is about one-quarter of an inch longer than the posterior. 

 Its narrowest diameter is about the middle, and in 

 making an examination with the speculum auris the in- 

 strument should not be introduced further than this point. 

 It must be borne in mind that in young children the 

 meatus is very shallow, the bony part consisting only of 

 a small ring of bone, deficient at the upper part, to which 

 the membrana is attached. 



To facilitate the introduction of the speculum, the au- 

 ricle should be drawn upwards, backwards, and a little 

 outwards ; this renders the canal tolerably straight. 



The membrana tympani is, on examination, grayish in 

 color, its fibrous structure looking radiated, slightly con- 

 ical, with the apex directed inwards, and placed very 

 obliquely at the bottom of the meatus. The handle of 

 the malleus is seen through the membrane, not quite 

 vertical, but inclining a little backwards. The points of 

 practical importance connected with the tympanum are 

 these that its upper aspect and floor are formed by thin 

 lamellae of bone separating it from the cranium and from 

 the canal for the internal carotid artery, so that disease 

 of the bone causes death, either by involving the dura 

 mater and brain, or from ulceration into the vessel. The 



