THE AUDITORY APPARATUS 215 



in relation to the posterior wall of the external acoustic meatus 

 are termed the " border cells," and when filled with pus they 

 may rupture into the meatus and discharge through it. 



Septic infection may spread from the tympanic antrum 

 (i) directly, by necrosis of bone, (2) by venous thrombosis, or 

 (3) by the lymph vessels. 



Upward Spread of Infection, which may or may not be 

 accompanied by destruction of the tegmen tympani, may cause 

 an extra-dural abscess in the middle cranial fossa or an abscess 

 in the temporal lobe of the brain. The veins which ascend 

 through the petro-squamous suture open into the superior 

 petrosal sinus, and through them the latter may become the 

 site of a septic thrombosis. Downward Spread involves the 

 internal jugular vein (p. 213). 



By necrosis of the lower part of the medial wall of the antrum 

 pus may pass downwards and medially, and reach the mastoid 

 notch (digastric fossa) Bezold's mastoiditis. It then passes 

 downwards along the styloid process and the muscles attached 

 to it, and gives rise to a deep-seated and dangerous form of 

 cervical cellulitis. Backward Spread involves the transverse 

 (lateral) sinus, and may pass along the cerebellar veins, producing 

 a cerebellar abscess. Forward Spread infects the " border cells," 

 and thence the pus may reach the external acoustic meatus, 

 or may spread laterally and produce an abscess which points on 

 the surface under cover of the auricle. When the pus reaches 

 the outer surface of the bone it strips up the periosteum and 

 forms a subperiosteal abscess. This accounts for the dis- 

 placement of the auricle in a downward and forward direction. 

 Abscesses in connection with the mastoid lymph glands (p. no) 

 lie superficial to the periosteum, and although they may displace 

 the auricle forwards, they are never accompanied by downward 

 displacement. Necrosis of the medial wall of the aditus exposes 

 the facial nerve, and infection may pass along its sheath to the 

 base of the brain, setting up a suppurative basal meningitis. 



Tuberculous disease of the temporal bone, a common condition 

 in children, may spread in any of the directions which have just 

 been described. In this case, and also in chronic otitis media, 

 the anterior auricular and the upper anterior group of the deep 

 cervical lymph glands are usually enlarged. 



The Surgical Approach to the Tympanic Antrum is 

 made through a curved incision, which commences a quarter 

 of an inch above the upper attachment of the auricle and extends 



14 c 



