.ANATOMY AND PHYSIOLOGY.
On the Muscles 'which open the Eustachian Tube. By Joseph
Toynbee, Esq., F. R. S.—The author commenced by alluding to the
opinion generally held by anatomists, viz:—That the guttural orifice of
the Eustachian tube is always open, and that the air in the tympanum
is constantly continuous with that in the cavity of the fauces. An ex-
amination of the guttural orifice of the tube in man and other animals
has led the author to conclude, that, except during muscular action, this
orifice is always closed, and that the tympanum forms a cavity distinct
and isolated from the outer air. The muscles which open the Eustachian
tube in man are the tensor and levator palati, and it is by their action,
during the process of deglutition, that the tubes are ordinarily opened.
That the act of swallowing is the means whereby the Eustachian tubes
are opened, is shown by some experiments, of which the following may
be cited :—If the mouth and nose be closed during the act of swallow-
ing the saliva, a sensation of fulness or distension arises from the air,
which is slightly compressed in the fauces, passing into and distending
the tympanic cavities. Upon removing the hand from the nose, it will
be observed that this feeling of pressure in the ears does not disappear,
but it remains until the act of deglutition is again performed, while the
nose is not closed. In this experiment the Eustachian tubes were opened
during each act of deglutition; during the first act, while they wTere
open, air was forced into the cavity of the tympanum by the contrac-
tion of the muscles of the fauces and pharynx, and the guttural orifices
of the tubes remained closed until the second act of swallowing, which
opened the tubes, and allowed the air to escape. That the act of de-
glutition opens the Eustachian tubes was inferred also from the custom
usually adopted of swallowing while the descent in a diving-bell is per-
formed ; by this act the condensed air is allowed to enter the tympanum,
and the sensation of pain and pressure in the ears is removed or entirely
avoided. The author gives an account of the Eustachian tube and its
muscles in mammalia, birds, and reptiles. In some mammalia the mus-
cles opening the tubes appertain as in man to the palate; in others, this
function is performed by the superior constrictor muscles of the pharynx.
In birds it is shown that there is a single membranous tube into which
the two osseous tubes open; this membranous tube is situated between,
and is intimately adherent to, the inner surface of each pterygoid mus-
cle, and by these muscles the tube is opened. The conclusion to which
the author arrives respecting the influence of the closed Eustachian
tubes, is, that the function of hearing is best carried on while the tym-
panum is a closed cavity, and that the analogy usually cited as existing
between the ordinary musical instrument the drum and the tympanum,
to the effect that in each it is requisite for the air within to communi-
cate freely with the outer air, is not correct. On the contrary, the
author shows that no displacement of the air is requisite for the propa-
gation of sonorous undulations, and that, were the Eustachian tubes con-
stantly open, these undulations would extend into the cavity of the
fauces, there to be absorbed by the thick and soft mucous membrane,
instead of being confined to the tympanic cavity, the walls of which are
so peculiarly well adapted to the production of resonance, in order that
they shall be concentrated upon the labyrinth.
In corroboration of the above views, the author states, that in cases
of deafness, dependent simply upon an aperture in the membrana tym-
pani, whereby the sonorous undulations are permitted to escape into the
external meatus, the power of hearing has been greatly improved by
the use of an artificial membrana tympani, made of very thin vulcanized
India-rubber or gutta percha, which is so applied as again to render the
tympanum a closed cavity.