. 



78 



THE EAR. 



measurements at certain points are given in the accompanying diagram. At the 

 inner extremity the tube is terminated by the membrana tympani, which is placed 

 obliquely, being inclined downwards, forwards, and towards the median plane ; and 

 thus, as shown in fig. 85, the floor of the meatus is longer than its roof. 



JT 



WT 



DIAGRAM SHOWING THE FORM 

 AND MEASUREMENTS OP 

 SECTIONS ACROSS THE 

 EXTERNAL AUDITOKY MKA- 

 TUS. (Bezold.) Natural 

 size. 



J., at commencement of 

 cartilaginous portion ; II. , 

 near end of cartilaginous por- 

 tion : ///., near beginning 

 of osseous portion ; IV., near 

 end of osseous portion. 



Structure. The wall of the meatus is composed partly of cartilage, and partly 

 of bone, and is lined by a prolongation of the skin. 



The cartilaginous part occupies somewhat less than half the length of the passage. 

 It is formed, as already mentioned, by an inflection of the deep part of the cartilage 

 of the pinna, but the cartilage does not form a complete boundary ; the tube being 

 deficient at the upper and posterior part where it is completed by fibrous membrane. 



The osseous portion is a little longer and on the whole rather narrower than the 

 cartilaginous part. At its inner end is a narrow groove (sulcus tympanicus), which 



Fig. 87. VIEW OF THE LOWER HALF OF THE AURICLE AND MEATUS IN THE LEFT EAR, DIVIDED BY A 

 NEARLY HORIZONTAL SECTION (after Rudinger). 



1, posterior wall : 2, anterior wall of the cartilaginous meatus ; 3, posterior wall of the bony meatus ; 

 4 to 5, membrane of the tympanum, with the handle of the malleus cut ; 6, stapes, to the right of 6, 

 section of the cochlea ; 7, stapedius muscle ; 8, section of facial nerve ; 9, tensor tympani muscle ; 

 10, branches of the auditory nerve to the cochlea, saccule, and utricle, 11. 



extends round the sides and floor of the meatus, but is deficient above ; into this 

 the margin of the membrana tympani is inserted. 



The sltin of the meatus is continuous with that covering the pinna, but is very 

 thin in the osseous part, especially at the bottom of the passage. Here it adheres 

 very closely to the periosteum, and has no hairs or glands, but is provided with 

 vascular papillae (ridges, according to Kaufmann). At the end of the tube the 

 skin is prolonged over the surface of the membrana tympani, forming the outer 

 layer of that structure. Towards the outer part of the roof of the osseous portion 

 and throughout the cartilaginous portion the skin possesses fine hairs and sebaceous 



