200 THE ORGANS OF SPECIAL SENSE 



referred symptoms in the distribution of the trigeminal or of the 

 vagus nerve. In this way a small piece of inspissated ear-wax 

 may be sufficient to set up a "focus of irritation" (p. 195) 

 in the nucleus of the vagus, and so give rise to intractable 

 coughing or chronic dyspepsia. 



In syringing the external acoustic meatus for the removal of 

 cerumen, foreign bodies, etc., the nozzle of the instrument 

 should be inserted at the postero-superior quadrant, so that it 

 does not impede the outflow of the fluid employed. 



Otoscopic examination will be dealt with when the tympanic 

 membrane is described. 



The Cavum Tympani, or Middle Ear, is an air-space in 

 the interior of the petrous portion of the temporal bone. 

 Anteriorly, it communicates with the naso-pharynx through 

 the auditory (Eustachian) tube, while, posteriorly, it opens 

 into the tympanic (mastoid) antrum. These three structures 

 are all lined with muco-periosteum, which is directly con- 

 tinuous with the mucous membrane lining the pharynx. That 

 part of the middle ear which lies above the upper border of 

 the tympanic membrane is termed the epitympanic recess (attic], 



Suppurative conditions of the middle ear are of frequent 

 occurrence, especially following the exanthemata, and on this 

 account the relations of the cavity are of great importance. 



The roof of the middle ear is formed by a moderately thin 

 plate of bone, termed the tegmen tympani, which separates the 

 cavity from the middle fossa of the skull and the temporal lobe 

 of the brain. Upward spread of septic processes in the middle 

 ear may give rise to meningitis or extra-dural abscess (i.e. 

 between the tegmen tympani and the dura mater), or it may 

 lead to the formation of an abscess in the temporal lobe of 

 the brain. (Forty per cent, of all cerebral abscesses occur in 

 the temporal lobe and can be referred to this cause.) 



The floor of the middle ear is formed by a plate of bone, 

 which separates the cavity from the jugular foramen and the 

 commencement of the internal jugular vein. The latter 

 structure may become the site of a septic thrombosis, if down- 



