The Ear. 447 



Diseases. The dermal or lining membrane of the 

 external auditory meatus is closely attached to the under- 

 lying structures so that inflammatory action in the canal 

 is attended with considerable pain, as a rule. This is seen, 

 for instance, in furunculosis, when the furuncles or boils 

 are present in the meatus. The anterior wall of the canal 

 is in relation with the parotid gland and with the condyle 

 of the lower jaw the gland resting against the car- 

 tilaginous portion, while the condyle of the jaw is in front 

 of the osseous part. When pus forms in the parotid gland 

 it may burrow into the meatus through two fissures or 

 clefts in the lower portion of the canal the fissures of 

 Santorini which are filled with fibrous tissue ; or, on the 

 other hand, inflammation of the meatus may spread 

 through these clefts to the parotid gland. Further, since 

 the posterior wall of the canal is separated from the mas- 

 toid cells by a thin layer of bone only, inflammation of the 

 wall of this canal may spread to these cells. 



The Tympanum or middle ear is about half ah 

 inch, from above downwards, and the same distance from 

 before backwards, and about one-sixth of an inch in width. 

 The middle ear is separated from the meatus by the mem- 

 brana tympani, which presents a depression about its 

 centre the umbo caused by the traction of the 

 tip of the handle of the malleus, where it is attached to 

 the membrane. The middle ear is lined with mucous 

 membrane, which is continuous with that of the naso- 

 pharynx through the Eusitachian tube, and which blends 

 with the mucous covering of the mastoid antrum and cells. 

 The roof of the tympanum separates the middle ear from 

 tthe cranial cavity, but gives passage to the numerous 

 small veins that empty into the veins of the dura mater 

 from this part of the ear, thereby offering free chan- 

 nels for the passage of septic processes from the tympa- 



