THE MIDDLE EAR 



687 



as a vascular layer of the mucosa in the mastoid cells, as well as in 

 the general tympanic cavity. 



THE TYMPANIC MEMBRANE 



The tympanic membrane is a 

 thin delicate partition which is 

 formed by a reflection of, the 

 cutaneous layer of the external 

 acoustic meatus on the one hand, 

 the tympanic mucosa on the 

 other, and between these two 

 membranes a layer of dense fi- 

 brous tissue whose tendinous 

 bands are disposed in radial and 

 circular directions. The margin 

 of the tympanic membrane is in- 

 serted into a fibrocartilaginous 

 ring which rests upon a bony ele- 

 vation, the annulus tympanicus. 



The slender manubrium or 

 handle of the malleus projects 

 from the superior margin of the 

 ring and is inserted between the 

 folds of the tympanic membrane, 

 extending downward to about the 

 center of the membrane, at which 

 point is the deepest part of its 

 concavity, its umbo. The bony 

 handle of the malleus, lying be- 

 tween the cutaneous and mucous 

 layers of the tympanic membrane, 

 is covered by a thin cartilaginous 

 layer, and receives the insertions 

 of the tendinous fibers. These 

 fibers are divisible into an outer 

 radial layer which extends from 

 the fibrocartilaginous ring at the 



periphery inward to the manubrium mallei, and an inner circular layr s 

 whose thickest portions are found close to the manubrium and near tne 



FIG. 573. TRANSECTION OF THE TYM- 

 PANIC MEMBRANE OF A CHILD. 



a, a', fibrocartilaginous ring; b, b', bone; 



c, c', skin of the external acoustic meatus; 



d, d', tympanic mucosa; e, cutaneous layer 

 of the tympanic membrane; /, fibrous 

 layer, obliquely cut at/'; g, layer derived 

 from the tympanic mucosa; h, handle of 

 the malleus; i, blood-vessels. Hematoxy- 

 lin and eosin. X 11. (After Kolliker.) 



