Page 32 - My FlipBook
P. 32
f ;
16 OF THE MUSCLES OF THE LOWER-JAW.
where there is so much motion. Accordingly, I find this car-
tilage in the different tribes of Carnivorous Animals, where
there is no eminence and cavity, nor other apparatus for
grinding ; and where the motion is of the true ginglimus kind
only.
In the Lower-Jaw, as in all the joints of the body, when the
motion is carried to its greatest extent, in any direction, the
muscles and ligaments are strained, and the person made
uneasy. The state, therefore, into which every joint most
naturally falls, especially when we are asleep, is nearly in the
middle, between the extremes of motion ; by which means all
the muscles and ligaments are equally relaxed. Thence it is,
that commonly, and naturally, the Teeth of the two Jaws are
not in contact ; nor are the Condyles of the Lower-Jaw so far
back in the Temporal Cavities as they can go.
OF THE MUSCLES OF THE LOWER-JAW.
Having described the figure, Articulation, Motion, and use
of the Lower-Jaw, it will be necessary, in the next place, to
give some account of the Muscles that are the causes of its
motion.
There are five pair of Muscles, each of them capable of pro-
ducing various motions, according to the situation of the Lower-
Jaw, whether they act singly, or in conjunction with others
and two or more of them may be so situated, as to be capable of
moving the Jaw in the same direction
; and every motion is
produced by the action of more than one Muscle at a time.
Thus, if the Jaw is depressed, and brought to one side, either
the Masseter, Temporal, or Pterygoidgeus internus of the opposite
may be applicable to the movements of the condyle in the human sub-
ject, it cannot be extended to the motion of the joint in the large
Carnivora in which animals, nevertheless, a
; spiral direction of the
articular surface is well seen. This spiral appearance of the articular
surface in the Felidce is clearly dependant on the disposition of the
anterior and posterior articular processes, the post-glenoid being most
developed internally, whilst the anterior ridge is necessarily more
external to permit the play of the contiguous coronoid process.
16 OF THE MUSCLES OF THE LOWER-JAW.
where there is so much motion. Accordingly, I find this car-
tilage in the different tribes of Carnivorous Animals, where
there is no eminence and cavity, nor other apparatus for
grinding ; and where the motion is of the true ginglimus kind
only.
In the Lower-Jaw, as in all the joints of the body, when the
motion is carried to its greatest extent, in any direction, the
muscles and ligaments are strained, and the person made
uneasy. The state, therefore, into which every joint most
naturally falls, especially when we are asleep, is nearly in the
middle, between the extremes of motion ; by which means all
the muscles and ligaments are equally relaxed. Thence it is,
that commonly, and naturally, the Teeth of the two Jaws are
not in contact ; nor are the Condyles of the Lower-Jaw so far
back in the Temporal Cavities as they can go.
OF THE MUSCLES OF THE LOWER-JAW.
Having described the figure, Articulation, Motion, and use
of the Lower-Jaw, it will be necessary, in the next place, to
give some account of the Muscles that are the causes of its
motion.
There are five pair of Muscles, each of them capable of pro-
ducing various motions, according to the situation of the Lower-
Jaw, whether they act singly, or in conjunction with others
and two or more of them may be so situated, as to be capable of
moving the Jaw in the same direction
; and every motion is
produced by the action of more than one Muscle at a time.
Thus, if the Jaw is depressed, and brought to one side, either
the Masseter, Temporal, or Pterygoidgeus internus of the opposite
may be applicable to the movements of the condyle in the human sub-
ject, it cannot be extended to the motion of the joint in the large
Carnivora in which animals, nevertheless, a
; spiral direction of the
articular surface is well seen. This spiral appearance of the articular
surface in the Felidce is clearly dependant on the disposition of the
anterior and posterior articular processes, the post-glenoid being most
developed internally, whilst the anterior ridge is necessarily more
external to permit the play of the contiguous coronoid process.
