630 



THE EAR. 



Vessels and nerves of the pinna. — The posterior auricular artery, a branch 

 from the external carotid, is distributed chiefly on the posterior or inner surface, 

 but sends small branches round and through the cai-tilage to ramify on the outer 

 sui-face of the pmna. Besides this artery, the auricle receives others — the ante- 

 rior auricular from the temporal in front, and a small artery from the occipital 

 behind. 



The i-ei?is correspond much in their course with the arteries. They join the 

 temporal vein, and their blood is returned therefore through the external jugular. 



The ffi-eat auricular iierve, from the cervical plexus, supplies the greater part 

 of the back of the auricle, and sends small filaments with the posterior auricular 

 artery to the outer surface of the lobule and the part of the ear above it. The 

 ■j)osterior auricular nerve derived from the facial, after communicating with the 

 aurumlar branch of the pneumogagtric, ramifies on the back of the ear and sup- 

 plies the retrahent muscle. The upper muscles of the auricle receive their supply 

 from the temporal branches of the same nerve. The auriculo-temporal branch of 

 the third division of the fifth nerve gives filaments chiefly to the outer and ante- 

 rior surface of the pinna. 



4i4 



THE EXTERNAL AUDITORY CANAL. 



The external auditory canal, meatus audiiorius extermis (fig. 440), 

 extends from the bottom of the concha (2) to the membrane of the 

 tympanum (2'), and serves to convey the vibrations of sound to the 

 middle chamber of the ear. The canal is about one inch and a quarter 

 in length. In its inward course it is inclined somewhat forwards 

 (fig. 444) ; and it presents likewise a distinct vertical curve (fig. 440), 



being directed at first somewhat up- 

 wards, and afterwards turning over a 

 convexity of the osseous part of its floor, 

 and dipping downwards to its termina- 

 tion, — a change of direction which must 

 be borne in mind by the surgeon in in- 

 troducing specula into the ear. The 

 calibre of the passage is smallest about 

 the middle. The outer opening is largest 

 from above downwards, but the inner 

 end of the tube is slightly widest in the 

 transverse direction. At the inner ex- 

 tremity the tube is terminated by the 

 membrana tympani, which is placed 

 obliquel)', with the inferior margin in- 

 clined towards the mesial plane; and 

 thus, as shown in fig. 440, the floor of 

 the meatus is longer than its roof. 



The meatus is composed of a tube 

 partly cartilaginous and partly osseous, 

 and is lined by a prolongation of the 

 skin of the pinna. 



The cartilaginous part occupies some- 

 what less than half the length of the 

 passage. It is formed by the deep part 

 of the cartilage of the pinna, already 

 described. 



The osseous portio7i is a little longer 

 and rather narrower than the cartilaginous part. At its inner end it 



Fig. 444. — View of the Lower 

 Half of the AuRiciiE and 

 Meatus in the Left Ear divided 

 BY a Horizontal Section (after 

 Sommerring) 



1 and 2, cut surfaces of the bony 

 part of the meatus ; 3, cut surface of 

 the cartilage of the pinna ; 4, external 

 meatus with the openings of nume- 

 rous ceruminous glands indicated ; 

 5, lobule ; 6, membrane of the 

 tympanum ; 7, dura mater lining of 

 the skull. 



