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raise the larynx. But, although they have this effect, a
proper attention to what happens in the living body will pro-
bably show, that their principal action is to depress the lower
jaw ; and that they are the muscles which are commonly em-
ployed for that purpose. Let a finger be placed on the upper
part of the mastoideus muscle, just behind the posterior edge
of the mastoid process, about its middle, touching that edge
a little with the finger ; then depress the lower jaw, and
the posterior head of the digastric will be felt to swell very
considerably, and so as to point out the direction of the mus-
cle. In this there can be no deception ; for there is no other
muscle in this part that has the same direction ; and those
who are of opinion that the digastric does not depress the
lower jaw, will more readily allow this, when they are told,
that we find the same head of the muscle act in deglutition,
but not with a force equal to that which it exerts in depressing
the lower jaw. Further, if the sterno-hyoidsei, sterno-thy-
roidaea, and costo-hyoideei, acting at the same time with the
mylo-hyoidei, and genio-hyoidaei assisted in depressing the
jaw, the os-hyoides and thyroide cartilage, would probably
be depressed, as the bellies of the sterno-hyoidsei, and of
the other lower muscles, are by much the longest ; but, on
the contrary, we find that the os-hyoides with the thyroide
cartilage, is a little raised in the depression of the jaw, which
we may suppose to be done by the anterior belly of the digas-
tric : and secondly, if these muscles were to bring about this
motion of the jaw, these parts would be brought forwards
nearer to the straight line between the chin and sternum,
which is not the case in this action whereas we find it to be
the case in deglutition, in which these evidently act. By ap-
plying our fingers upon the genio-hyoidaeus, and mylo-hy-
oidaeus, near the os-hyoides, between the two anterior of
the digastric, (not near the chin where the action of these