for the motion of the limbs,
must, it is evident in their way from the trunk of the body to the place
of their destination, travel over the moveable joints; and it is no less
evident that in this part of their course they will have from sudden
motions, and from abrupt changes of curvature, to encounter the danger
of compression, attrition, or laceration. To guard fibres so tender
against consequences so injurious, their path is in those parts
protected with peculiar care; and that by a provision in the figure of
the bones themselves. The nerves which supply the fore arm, especially
the inferior cubital nerves, are at the elbow conducted by a kind of
covered way, between the condyle, or rather under the inner
extuberances, of the bone which composes the upper part of the arm. At
the knee the extremity of the thigh-bone is divided by a sinus or cliff
into two heads or protuberances; and these heads on the back part stand
out beyond the cylinder of the bone. Through the hollow which lies
between the hind parts of these two heads, that is to say, under the
ham, between the ham strings, and within the concave recess of the bone
formed by the extuberances on either side; in a word, along a defile
between rocks pass the great vessels and nerves which go to the leg. Who
led these vessels by a road so defended and secured? In the joint at the
shoulder, in the edge of the cup which receives the head of the bone, is
a notch which is covered at the top with a ligament. Through this hole
thus guarded the blood-vessels steal to their destination in the arm
instead of mounting over the edge of the concavity."[17]

. . . . . .

"What contrivance can be more mechanical than the following, viz.: a
slit in one tendon to let another tendon pass through it? This structure
is found in the tendons which move the toes and fingers. The long
tendon, as it is called in the foot, which bends the first joint of the
toe, passes through the short tendon which bends the second joint; which
course allows to the sinews more liberty and a more commodious action
than it would otherwise have been capable of exerting. There is nothing,
I believe, in a silk or cotton mill, in the belts or straps or ropes by
which the motion is communicated from one part of the machine to another
that is more artificial, or more evidently so, than this perforation.

"The next circumstance which I shall mention under this head of
muscular arrangement, is so decidedly a