tilages, ligaments, and synovial membrane are
insensible when in health; yet they are supplied with organic nerves,
as well as with arteries, veins, and lymphatics.

_Observation._ The joints of the domestic animals are similar in their
construction to those of man. To illustrate this part of the body, a
fresh joint of the calf or sheep may be used. After divesting the
joints of the skin, the satin-like bands, or ligaments, will be seen
passing from one bone to the other, under which may be observed the
membranous bag, called the capsular ligament. This is very smooth, as
it is lined with the soft synovial membrane, beneath which will be
seen the cartilage, that may be cut with a knife, and under this the
rough extremity of the ends of the bones.

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117. Of what are ligaments composed? What is the appearance of these
bands? Where are they found? 118. With what vessels are the cartilages
and ligaments supplied? How can the structure of the joints be
explained?

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CHAPTER VI.

PHYSIOLOGY OF THE BONES.

119. The bones are the framework of the system. By their solidity and
form, they not only retain every part of the fabric in its proper
shape, but afford a firm surface for the attachment of the muscles and
ligaments. By means of the bones, the human frame presents to the eye
a wonderful piece of mechanism, uniting the most finished symmetry of
form with freedom of motion, and also giving security to many
important organs.

120. To give a clear idea of the relative uses of the bones and
muscles, we will quote the comparison of another, though, as in other
comparisons, there are points of difference. The "bones are to the
body what the masts and spars are to the ship,--they give support and
the power of resistance. The muscles are to the bones what the ropes
are to the masts and spars. The bones are the levers of the system; by
the action of the muscles their relative positions are changed. As the
masts and spars of a vessel must be sufficiently firm to sustain the
action of the ropes, so the bones must possess the same quality to
sustain the action of the muscles in the human body."

121. Some of the bones are designed exclusively for the protection of
the organs which they enclose. Of this number are those that form the
skull, the sockets of the eye, and the cavity of the nose. Others, in
addition to the protection they give to important organs, are us