OF THE MUSCLES. 
75 
to point out instances in which, and properties with respect 
to which, the disposition of these muscles is as strictly 
mechanical, as that of the wires and strings of a puppet.* 
I. We may observe, what I believe is universal, an ex¬ 
act relation between the joint and the muscles which move 
it. Whatever motion the joint, by its mechanical construc¬ 
tion, is capable of performing, that motion, the annexed 
muscles, by their position, are capable of producing. For 
example; if there be, as at the knee and elbow, a hinge- 
joint, capable of motion only in the same plane, the lead¬ 
ers, as they are called, i. e. the muscular tendons, are 
placed in directions parallel to the bone, so as, by the con¬ 
traction or relaxation of the muscles to which they belong, 
to produce that motion and no other. If these joints were 
capable of a freer motion, there are no muscles to produce 
it. Whereas at the shoulder and the hip, where the ball 
and socket joint allows by its construction of a rotatory or 
sweeping motion, tendons are placed in such a position, 
and pull in such a direction, as to produce the motion of 
which the joint admits. For instance, the sartorius or 
tailor’s muscle, rising from the spine, running diagonally 
across the thigh, and taking hold of the inside of the main 
bone of the leg, a little below the knee, enables us, by its 
contraction, to throw one leg and thigh over the other; 
giving effect, at the same time, to the ball and socket joint 
at the hip, and the hinge-joint at the knee. [PI. XII. fig. 1.] 
There is, as we have seen, a specific mechanism in the 
bones, for the rotatory motions of the head and hands; there 
is, also, in the oblique direction of the muscles belonging to 
them, a specific provision for the putting of this mechanism 
of the bones into action. [PI. XII. fig. 2.] And mark the 
consent of uses. The oblique muscles would have 
been inefficient without that particular articulation; that 
particular articulation would have been lost, without the 
oblique muscles. It may be proper, however, to observe 
with respect to the head, although I think it does not vary 
the case, that its oblique motions and inclinations are often 
motions in a diagonal , produced by the joint action of mus- 
* Muscles are the fleshy parts of the body which surround the bone3, 
having a fibrous texture; a muscle being composed of a number of mus¬ 
cular faciculi, which are composed of fibres still smaller; these result 
from fibres of a less volume, until by successive division we arrive at 
very small fibres no longer divisible. These muscular fibres are longer 
or shorter according to the muscles to which they belong; and every fi¬ 
bre is fixed by its two extremities to tendon or aponeurosis , which are 
the “ wires and strings ” which conduct the muscular power when they 
contract— Paxton . 
