These last muscles form a class; they raise the upper lip and
the angle of the mouth so as to expose the canine teeth even in
man. We shall find them to be very strong in the carnivorous
animals, while there is no such action to be performed in the milder
class of graminivorous animals. If these muscles be in action contrary
to the circular fibres of the lips, there is a painful and bitter
expression; but if they are influenced along with the orbicularis
oris and orbicularis palpebrarum, if the former of these muscles be
relaxed, and the other contracted, there is a fulness of the upper
part of the face, and a cheerful smiling expression of countenance.
k . The O r b i c u l a r i s M u s c l e of the bps. This is a circular muscle,
which forms much of the fleshy substance of the lips. It closes
the mouth ; when allowed to act fully, it purses the lips ; it is
the antagonist or opponent to the other muscles which are
inserted or fixed into the lips.
l . The N a s a l i s L a b ii S u p e r i o r i s . This muscle draws down
the septum of the nose, and belongs to a former class of
muscles,
n . T r i a n g u l a r i s O r i s , or D e p r e s s o r L a b io r u m . A strong muscle
arising from the base of the lower jaw, and inserted into the
angle of the mouth.
o. Q u a d r a t u s M e n t i , or depressor of the lower lip.
p. The L e v a t o r e s M e n t i . These are small but strong muscles,
which, arising from the lower jaw near the alveolar processes
of the incisor teeth, descend, and are fixed into the integument
of the chin; so that by their action they throw up the chin
and project the lower lip.
q . The B u c c in a t o r , is a muscle which forms the flesh of the cheek.
It is principally for turning the morsel in the mouth, and
is particularly strong in the graminivorous and ruminating
animals. In broad laughter it retracts the lips.
These are muscles of mastication no doubt, but their perfection
arises from their adaptation to speech and expression. The orbicularis
muscle is singularly affected in the various emotions of the
mind, trembling and relaxing, both in joy and grief. It relaxes
pleasantly in smiling ; it is more drawn by the superiority of its
opponent in weeping.
The union of so many muscles in the angle of the mouth produces
the fleshy prominence so peculiar to those who have a thin
face, and are at the same time muscular. When the cheeks are fat
and full, it is the action of these muscles which produces the
dimpled cheek.
The angle of the mouth is full of expression, as the orbicularis,
the superior, or the inferior' class of muscles attached here, have the
preponderance in action.
The Triangularis muscle and the Levator Menti combining,
give rise to expression peculiar to man. The angle of the mouth