THE MEMBRANA TYMPANI 



735 



may be increased or diminished by the action of the muscles of the 

 middle ear. The point of greatest concavity, where the extremity of 

 the handle of the malleus is attached, is called the umbo. On the inner 

 surface of the membrane are two pouches, or pockets. One is formed 

 by a small, irregular, triangular fold, situated at the upper part of its 

 posterior half and consisting 

 of a process of the fibrous 

 layer. This, which is called 

 the posterior pocket, is open 

 below and extends from the 

 posterior upper border of 

 the membrane to the handle 

 of the malleus, which it as- 

 sists in holding in position. 

 " After it has been divided, 

 the bone is much more 

 movable than before" 

 (Troltsch). The anterior 

 pocket is lower and shorter 

 than the posterior. It is 

 formed by a small bony 

 process turned toward the 

 neck of the malleus, by 

 the mucous membrane, by 

 the bony process of the mal- 

 leus, by its anterior liga- 

 ment, the chorda tympani 



and the anterior tympanic Fig. 190. Right membrana tympani, seen from within, x 6. 



artery. The handle of the 

 malleus is inserted between 



Reduced about one-fifth from a photograph (Riidinger). 



I, head of the malleus, divided; 2, neck of the malleus; 

 3, handle of the malleus, with the tendon of the tensor-tym- 



the two layers Of the fibrOUS P am muscle; 4, divided tendon of the tensor tympani; 5, 6, 



structure of the membrana 



portion of the malleus between the layers of the membrana 

 tympani ; 7, outer (radiating) and inner (circular) fibres of 



and OCCUDieS the t ^ ie membrana tympani; 8, fibrous ring of the membrana 

 tympani; 9, 14, 15, dentated fibres, discovered by Gruber; 

 Upper half Of its Vertical di- 10, posterior pocket ; ii, connection of the posterior pocket 



ameter, extending from the ^* e the malleus; I2> anterior pocket; I3 ' chorda-tympani 

 periphery to the umbo. 



The membrana tympani, though thin and translucent, presents three 

 distinct layers. Its outer layer is a very thin extension of the integu- 

 ment lining the external meatus, presenting, however, neither papillae 

 nor glands. The inner layer is a delicate continuation of the mucous 

 membrane lining the tympanic cavity and is covered with tessellated 

 epithelial cells. The fibrous portion, or lamina propria, is formed of 



