Chap, v.] THE EAR. 63 



The posterior wall separates the meatus from the 

 niastoid cells, and through this partition inflammation 

 may extend from one part to the other, especially as 

 the cartilage of the tube is deficient at its upper and 

 posterior parts. The inferior wall of the bony meatus 

 is very dense and substantial, and corresponds to the 

 vaginal and styloid processes. 



Blood supply. The pinna and external meatus 

 are well supplied with blood by the temporal and 

 posterior auricular arteries, the meatus receiving also 

 a branch from the internal maxillary. In spite of 

 this supply, the pinna is frequently the seat of 

 gangrene from frost-bite. This is due to the fact that 

 all the vessels are superficial and are close beneath the 

 surface, that the part is much exposed to cold, and 

 that the pinna lacks the protection of a covering of 

 fat. The same conditions predispose to gangrene of 

 the nose from external cold. Bloody tumours 

 (hsematomata) are often met with on the pinna, and 

 are said to be more common in lunatics. They 

 appear to be frequently due to injury, and consist of 

 an extravasation between the perichondrium and the 

 cartilage. 



Nerve supply. The outer surface of the pinna 

 is supplied by the auriculo-temporal nerve, with the 

 exception of the skin over the antitragus, the vertical 

 part of the antihelix, the corresponding part of the 

 helix and its fossa, and the lobule, which parts are 

 all supplied by the great auricular nerve. The inner 

 surface is almost entirely supplied by the latter nerve, 

 the small occipital nerve giving a branch to the 

 upper extremity, and Arnold's nerve a branch to the 

 back of the concha, near the mastoid process. The 

 meatus is supplied mainly by the auriculo-temporal, 

 with, in addition, a contribution from Arnold's nerve, 

 which goes to the lower and back part of the canal, 

 not far from its commencement. Arnold's nerve, a 



