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OF THE MUSCLES OF THE LOWER-JAW. 17
side will not only raise the Jaw, but bring it to its middle state.
It will be necessary in the description of each Muscle, to give
its use in the different situations of the Jaw ; by which means,
after they are all described, their compound actions will be
better understood. I shall first describe those which raise the
Jaw ; then those which give it the lateral motion ; and lastly,
those which depress it ; proceeding in each class as they rise
in dissection.
The most superficial is the Masseter : it is situated upon the
posterior and lower part of the Face, between the cheek-bone,
and angle of the Lower-Jaw, directly before the lower part of
the Ear. It is a thick, short, complex Muscle, and a little
it appears to have two distinct origins, an anterior
flattened :
outer, and a posterior inner ; but that is owing only to its outer
edge at its origin being slit, or double ; and the fibres of these
two edges having a different course, decussating each other a
little. The anterior, and outer portion of the Muscle begins to
rise from a small part of the lower edge of the Malar Process
of the Maxillary Bone, adjoining to the Os Malse ; and con-
tinues its origin all along the lower horizontal edge of this last
bono, to the angle where its Zygomatic Process turns up, to
join that of the Temporal Bone. The external layer of fibres
in this portion are tendinous at their beginnings, while the
internal are fleshy.
The posterior and inner portion of this Muscle begins to rise
partly tendinous, and partly fleshy, from the same lower edge of
the Os Malse ; not where the origin of the other portion ter-
minates, but a little farther forwards ; and this origin is con-
tinued along the lower edge of the Zygomatic Process of the
Temporal Bone, as far backwards as the eminence belonging to
the articulation of the Lower-Jaw.
From this extent of its origin, the Muscle passes downwards
to its insertion into the Lower-Jaw. The anterior external por-
tion is broader at its insertion than at its origin ; for it occupies
a triangular space of the Lower-Jaw above the angle, and on
the outside, of about an inch in size, to about an inch and a