THE MEMBRANA TYMPANI IN THE HUMAN EAR. 
165 
the effect of imparting^ great strength to the membrane, while it preserves its extreme 
delicacy and tenuity. It has been stated that there is no evidence to prove that the 
fibres, of which the membrana tympani is composed, possess in themselves any con- 
tractile power ; neither do the component fibres of the laminae appear to evince more 
than an extremely slight degree of elasticity. An examination however of the struc- 
ture after death shows that it has an inherent power of returning to its natural state 
of tension after being unusually distended. Thus, if the membrana tympani be 
exposed without interfering with its natural state of tension, and the canal containing 
the tensor tympani muscle be laid open, so that that muscle can be drawn towards 
its origin, the external concavity of the membrana tympani can be increased till it 
becomes very tense, but as soon as the muscle is let go the membrana tympani will 
be observed to resume its former condition. This action is explainable partly by the 
slight elasticity of the circular cartilaginous band, into which the peripheral extremi- 
ties of the radiating fibres are inserted, and partly by the slight elasticity of these 
fibres themselves, but more especially by the peculiar arrangement of the circular 
fibrous lamina, which it will be remembered has always a tendency, when left to 
itself, to assume a more shallow form. Thus, when the membrane is rendered very 
concave, the circular fibres are slightly separated from each other; but when the 
extra tension ceases, the fibres intersecting the circular ones aid in drawing the 
latter together again. 
The disposition of the central part of the circular lamina also assists it in the 
function of bringing back the membrana tympani to its natural state after tension 
by the tensor tympani muscle. It has been stated that the middle part of these 
circular fibres, instead of being attached to the handle of the malleus, are applied 
against its inner surface, and thus the membrane is rendered tense by the pressure 
of the long process of the malleus against its outer surface during the action of the 
tensor tympani muscle, and when this muscle ceases to act the central part of the 
circular layer of fibres reacts on the malleus, and constrains it to resume its usual 
position. Besides the office of bringing the membrana tympani to its natural state 
after the action of the tensor tympani muscle, the circular fibrous layer would appear 
to be always acting as an antagonist to the tensor tympani ligament, and by the 
continued action of these two tissues, the one drawing it inwards, the other outwards, 
the membrana tympani is kept in a state adapted to receive all the ordinary sonorous 
undulations, independent of the exercise of any muscular power. 
