TIIE PHYSIOLOGY OF THE INTRA-TYMPANIC 
MUSCLES. 
By S. O. Richey, M. D., Washington, D. C. 
"Self-preservation is the first law of Nature” is axio- 
matic, but the usual interpretation of the proverb is in its 
relation to volition. The true significance of the expres- 
sion is much broader, for Nature acts according to this 
law regardless of the judgment, or aid, of the individual, 
though not always successfully in face of his opposition. 
More than this, Nature places a premium of the better 
development of power, or dexterity, and facility in action 
upon the proper and rational use of the means of protec- 
tion which she affords. "Struggle for existence” presup- 
poses that it is difficult to live ; that there is opposition to 
continued existence with which all animals have to con- 
tend. Opposition indicates effort; effort suggests means, 
purpose, and development. 
In a paper on "The Primary Physiological Purpose of the 
Membrana Tympani,” read in September, 1888, at Wash- 
ington, D. C., an intention for the drum-membrane other 
than the transmission of sound impulses was discussed. 
From it follows a deduction as to use of the intra-tympanic 
muscles, an addition to this function as ordinarily under- 
stood. 
If the membrana tympani in purpose protects the aural 
tissues lying interior to it, these muscles being appendages 
to the membrane are designed to assist the purposes of the 
membrane, which they do in part by 'protecting it from 
injury by the impact upon it of sound impulses violent 
enough to rupture an inflexible membrane, firmly attached, RICHEY. 
and having such a plane as to expose it to the fullest force 
of the concussion. The membrana tympani fulfills but 
one of these conditions ; it is attached. " I think it 
may be fairly inferred that the fundtion of the tensor tym- 
pani muscle is to protect' the membrana tympani and the 
labyrinth from injury during loud sounds; while the 
stapedius muscle places these structures in a position to be 
impressed by the most delicate vibrations.” (Toynbee, 
"On the Functions of the Muscles of the Tympanum in the 
Human Ear,” British and Foreign Medico-Chirurgical 
Review, 1853.) Henle (Eingeweidelehre, p. 749) thinks 
the stapedius acts as a guard, when the stapes might, by 
undue force, be driven into the oval window. "A violent 
blow on the ear with the palm of the hand rarely produces 
mischief to the membrana tympani when its reception is 
expected;' whereas a comparatively gentle but unexpected' 
blow frequently produces, not merely concussion of the 
nervous labyrinth and serious derangement of the functions, 
but not uncommonly ruptures the membrana tympani 
itself.” (Toynbee, Dis. of the Ear, 1860, Philadelphia, p. 
206.) Toynbee refers to previous writers, Mons. F. 
Savart in 1822, Mr. C. Brooke in 1843, and later Profes- 
sors Todd and Bowman, as taking the same view of the 
subjedt; that the membrana tympani with its appendages, 
the ossicles and muscles, is in function analagous to 
the iris. However much we might expedf to find some 
conclusive statement upon so important a subjedf in the 
chapters devoted to physiology in later treatises upon the 
ear, I have not been so fortunate. The purpose of this part 
of the organ is indicated to be the transmission of sound, 
making reference to no other function, though that mucous 
membrane in other localities becomes dermoid in character 
when freely exposed abnormally is not questioned. 
The external meatus, containing cerumen and hairs, ad- 
1 Italics are mine. INTRA-TYMPANIC MUSCLES. 
3 
mits sound waves and affords protection to the drum-mem- 
brane : from inseCts, by the hairs and cerumen ; from solid 
foreign bodies, by the hairs, cerumen, and the shelve and 
direction of the canal; the curved course and the shape of 
the external meatus, flared at both extremities and nar- 
rowed in the middle, diminish the force of impaCt upon the 
drum-membrane of a column of compressed air: the 
oblique position of the membrane to the meatus, and its mo- 
tility aiding this effeCf. The most obvious purpose of the 
intra-tympanic muscles is that of adjustment of the mem- 
brane, by their involuntary aCtion, to the best condition of 
tension, or relaxation, and thus its relation to the column 
of air in the auditory meatus, to resist the sudden impaCt of 
air upon it. 
Contraction of the palatal muscles, and opening of the 
Eustachian tube, is prompted by excitation of the trigeminus 
and the consequent contraction of the tensor muscle (Volto- 
lini, Virchow’s Archiv., band, 65, p.467). The tensor tym- 
pani and the stapedius are supposed to be involuntary 
muscles the ligamentous bands a6t as supports. 
Deduction.—Contraction of the tensor tympani causes 
motion of the malleus towards the inner tympanic wall, 
produces tension of the ligamentous bands supporting the 
ossicular articulations, contraction of the palatal muscles, 
and opening of the Eustachian tube, admitting a column of 
renewing air to support the membrane against the pressure 
of the air from the direction of the external meatus. This 
aCtion is instinCtive and involuntary, a shrinking from ap- 
prehension. The trigeminus governs this, as it does the 
same aCtion of the eyelids. 
The muscles are kept in a state of perfeCt aCtion by their 
constant exercise in the performance of the other, and 
1 They are also somewhat subject to volition. RICHEY. 
possibly more important function of adjusting the trans- 
mitting apparatus to sound waves of varying values.1 
1 It would be interesting to know, if possible, whether in eases of 
rupture of the membrana tympani by aerial concussion any impairment 
of the process above described previously existed.