34 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. 



some of the more superficial have not become detached. It is obvious 

 also that we must bear in mind the frequent occurrence of patho- 

 logical alterations, in order to avoid forming an erroneous estimate of 

 the normal thickness. 



Independently, however, of these sources of error, I have satisfied 

 myself by numerous measurements, that the thickness of the cuticle 

 varies to a considerable extent in adults. How far the greater or less 

 development of the cuticle of the membrana tympani affects the sensi- 

 bility and the normal discharge of the physiological functions, cannot 

 at present be stated with certainty. From analogy to the skin generally, 

 we may however presume that the thinner the cuticle the greater the 

 sensibility. The thickness of the cuticle of the membrana tympani 

 in the new-born child favours the same view. 



The membrana propria is composed of sharply defined, 

 strongly refractive fusiform fibres, flattened laterally, and 

 having a diameter of 0'0036 O0108 of a millimeter. Under 

 certain circumstances these appear to be homogeneous, though 

 they are in reality fibrillated, as may be clearly demonstrated 

 by the addition of various reagents, as chromic acid, chloride 

 of gold, perosmic acid, etc. The fibres most closely resemble 

 tendinous fibres, and present the same chemical characters, 

 swelling up in solutions of potash and acetic acid, and becoming 

 isolated by the solution of their cement in baryta and lime 

 water. If the membrana tympani be boiled in dilute solution 

 of potash, it dissolves, only a small quantity of elastic tissue 

 remaining behind, of which part evidently belongs to the 

 vessels, whilst part appears in the form of a continuous 

 and very thin sheet, which probably forms the basement 

 membrane of the mucous layer on the inner surface of the 

 membrana tympani (Helmholtz, 11). The foetal membrana 

 tympani is particularly well adapted for the investigation of 

 these fibrillated bands. We here find that the membrana 

 propria is represented by distinct fasciculi of fibrils which pre- 

 sent all stages of development. No distinct limits exist, in the 

 earlier periods of development, between the connective tissue 

 of the cutis and the fibres representing the subsequently 

 developed membrana propria ; the difference is first distinctly 

 expressed towards the close of foetal life. 



The latter therefore (membrana propria) may be regarded 



