CHAPTER XXI. 



THE EAE. 

 BY DBS. WILLIAM P. WHITNEY AND CLARENCE J. BLAKE, OP BOSTON. 



FOLLOWING the natural order are to be considered, first, the 

 external ear with the meatus externus ; secondly, the middle 

 ear with the Eustachian tube; and thirdly, the internal ear 

 (membranous labyrinth and cochlea). 



External ear. This includes the auricle, the meatus exter- 

 nus, and the membrana tympani. 



The auricle is formed by a cartilaginous plate, 1-2 mm. in 

 thickness. The line elastic fibres of this plate, which is of the 

 reticular variety of cartilage, can be traced into the perichon- 

 drium, and even into the subcutaneous tissue. Both perichon- 

 drium and subcutaneous tissue are rich in elastic fibres, the 

 latter varying greatly in amount in different parts of the ear, 

 being very sparingly developed on the concave surfaces, where 

 the skin is closely adherent to the perichondrium, and immov- 

 able in consequence, but more abundant on the convex sur- 

 faces, where the skin is movable ; it forms, together with the 

 fat enclosed in its meshes, the bulk of the lobule. 



The cutis covering the auricle is a direct continuation of 

 that covering the face, and is well provided with downy hairs 

 and sebaceous glands. These latter reach their greatest devel- 

 opment in the depressions of the auricle, especially the concha. 



The external meatus consists of a cartilaginous and an os- 

 seous portion. The former only differs in structure from the 

 auricle into which it passes, in the presence of the ceruminous 

 glands. These are tubular glands, having a coil at the bottom. 

 They consist of a membrana propria, on which is a layer of 

 cubical epithelium, and are the analogues of the sweat-glands. 

 In the osseous portion of the meatus the glands are sparingly 

 found, and the hairs are fewer and finer. Otherwise there is 

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