688 



THE EAB 



periphery of the membrane; between these points the circular layer of 

 fibers is partially or entirely deficient. Just within the fibrocartilagi- 



nous ring at the periphery 

 of the membrane the cir- 

 cular layer of fibers 

 abruptly ends. 



The cutaneous layer 

 of the tympanic membrane 

 forms a very thin coat, its 

 epidermis consisting of a 

 germinal layer one* or two 

 cells deep, which is cov- 

 ered by several flattened 

 non-nucleated cells of the 

 horny portion. The derma 

 or corium is very thin, 

 contains no papillae, and 

 is intimately adherent to 

 the fibrous layers of the 

 membrane ; it contains 

 neither glands nor hairs. 

 The mucous layer of 

 the tympanic membrane 

 is even thinner than the 

 cutaneous. It consists of 

 a flattened entodermal 

 epithelium which rests al- 

 most directly upon the 

 layer of circular fibers. 

 A few connective tissue 

 fibers pass irregularly 

 from the mucous, through 

 the fibrous, to the cu- 

 taneous layer, thus firm- 

 ly uniting the several lay- 



Ji'liip 





''~**-&jS: 



FIG. 574. SECTION THROUGH THE MARGIN OP THE 

 TYMPANIC MEMBRANE OP A CHILD. 



a, fibrocartilaginous ring; 6, bone; c, derma of 

 the external auditory canal; d, tympanic mucosa; 

 e, e', epidermis; /, radial fibers, and /', circj^ar 

 fibers of the tympanic membrane; g, mucosa of the 

 membrane; h, epithelium of the tympanum; i, 

 blood-vessels. X 55. (After Kolliker.) 



ers into a compact mem- 

 brane. 



In the upper quadrant of the tympanic membrane, above the at- 

 tachment of the malleus, the fibrous layers are wanting; the mucous 

 and cutaneous layers are therefore in contact, and the membrane presents 



