366 



NORMAL HISTOLOGY. 



towards its periphery. At its lower end, the handle of the malleus is flat- 

 tened laterally and broadened at the umbo, which corresponds to the 

 deepest part of the concavity of the membrane. 



The tympanic membrane includes three main layers: (i) the middle or 

 fibrous stratum ; (2) \^ external or cutaneous layer, the prolongation of the 

 skin lining the external auditory canal; and (3) the internal or mucous mem- 

 brane, a continuation of the mucous membrane clothing other parts of the 

 tympanic cavity. 



The fibrous layer, the membrane proper, represents the mesodermic 

 portion of the drum-head and consists of an outer stratum of radially dis- 

 posed fibres which diverge 

 from the malleus towards the 

 periphery of the membrane, 

 and an inner stratum of circular 

 fibres, concentrically arranged 

 and best developed near the 

 periphery of the membrane 

 but absent at the umbo. The 

 radiating fibres, on the con- 

 trary, become more dense at 

 the umbo. Connective tissue 

 corpuscles, spindle-shaped in 

 longitudinal and stellate in 

 cross-section, lie between the 

 fibres of the two layers. At 

 the periphery of the membrane 

 proper, the fibres, especially 

 those of the radial stratum, are 

 connected with those of a ring 

 of thick connective tissue, the 

 annulus fibrosus. The fibres 

 of the annulus run in various 

 directions, but for the most part 

 radially, that is, towards the 

 tympanic membrane proper 

 (Fig. 416). Rounded con- 



Annulus tendinosus nective Cells lie between these 



fibres. 



The cutaneous layer 

 consists of a thin epidermal 



FIG. 415. Frontal section through tympanic membrane Stratum, Composed of tWO Or 

 and malleus, showing long process of the latter embedded tVit-pp rnwc r>f rpllc t\nc\ a <\e-\\ 

 within membrane. X 8. (Preparation by Dr. Ralph Butler.) 



cate sheet of connective tissue ; 

 neither a definite corium nor papillae are present. 



The mucous membrane covering the inner surface of the drum-head 

 consists of a scanty layer of connective tissue, invested with a sheet of large 

 low nonciliated epithelial cells. 



The blood-vessels of the tympanic membrane include arteries arranged 

 as an outer and an inner set, separated by the membrane proper. Each of 

 these sets forms a plexus of vessels, with a large branch extending down- 

 wards along the malleus-handle and another around the periphery of the 

 membrane, these two branches being connected by numerous radiating twigs. 

 Perforating vessels connect the two sets of arteries, especially along the 



Head of malleus 

 External ligament 

 Mem. flaccida or 

 Shrapnell's membrane 

 "Prussak's space 

 Neck 



Short process 

 Chorda tympani 



Tendon of tensor 



tympani 



Long process of 



malleus 



artilage 

 Epidermis 

 Membrana propria 



Mucous membrane 

 Membrana tympani 



