548 



THE AUDITORY APPARATUS 



24 mm., of which 8 mm. corresponds with the cartilaginous, 

 and 1 6 mm., with the bony part of the canal; but, as the 

 membrana tympani is placed obliquely, the anterior wall and 

 the floor are longer than the posterior wall and the roof, 

 respectively. Moreover, the diameter of the canal is not 

 uniform. It is narrowest at the isthmus, which lies about 

 5mm. from the tympanic membrane ; and its vertical diameter 

 is greatest at the lateral end, whilst its antero-posterior 

 diameter is greatest at its medial end. These facts must 

 be borne in mind during the removal of foreign bodies which 

 have made their way into the canal. As the tube passes from 



Osseous part of meatus 



Recessus 



epitympanicus 

 Malleus 

 Cochl 



Tympanum_L_ 

 Membrana 

 tympani 



Internal carotid 

 artery 



Crus antihelicis 

 inferior 



Cymba conchae 

 rus helicis 



Cartilaginous 

 part of meatus 

 Cavum conchae 



Lower boundary 

 of incisura 

 intertragica 



FIG. 233. Vertical transverse section through the Right Ear : anterior half 

 of section viewed from behind. (Howden.) 



the surface medially it describes a gentle sigmoid curve, but 

 its general direction is towards the median plane with a 

 slight inclination anteriorly. The skin lining the cartilaginous 

 portion is abundantly furnished with ceruminous glands and 

 is provided also with laterally directed hairs, which tend to 

 prevent the entrance of dust. The cutaneous lining of the 

 osseous part, which is thin and tightly adherent to the 

 subjacent periosteum, is destitute of hairs, and glands are for 

 the most part absent. The cutaneous lining of the meatus is 

 continued in the form of an exceedingly delicate layer over 

 the outer surface of the membrana tympani. 



