_Of the Bones, Muscles, Ligaments, Tendons, and their Connections._
The bones may be considered as the timber-work of the human frame; by
which this wonderful fabric is supported, and kept in its due form, that
the whole may be brought into its various movements, without confusion
or obstruction to each other.
The bones are the most solid parts of the human body, composed of hard
and indurated fibres, striated over each other, in a manner peculiar to
that substance. The bony fibres are in themselves insensible, yet as the
parts are variously distributed with arteries and veins, and that the
nerves must necessarily have a share in their formation, they have a
peculiar sensibility, which is perceptible in some parts more than
others; they cannot strictly speaking, be deemed quite insensible.
The whole bony frame is covered with a tendinous and nervous tegument,
called _periosteum_; except such parts of the teeth as are designed for
mastication, which are provided with a peculiar enamel, that is harder
than the rest of the bony substance.
The _periosteum_ is exquisitely sensible, and is the safe-guard to the
substance of the bone, which is delicately tender notwithstanding it is
not so sensible as the skin that covers it; insomuch that it will become
_carious_ on the least exposure to the air, or the attack of any foreign
body of matter whatever; whence in wounds and fractures in general,
great attention should be paid to the substance of the bone, being very
subject to become _carious_ and to _exfoliation_, which is of the
greatest consequence; but of this I shall say more in another place.
The marrow is principally designed for the nourishment of the bones;
which is evident from its being plentiest in young people, when the
bones are strongest; and that when it is deficient, they become brittle,
and lose their tenacity.
The marrow is contained in a cellular substance, partly in vesicles of a
nervous texture, and partly bony cells. At the ends of the long bones
the texture is more spungy than in the middle, where the cavity is less,
but the substance is most compact. Though anatomically there is no
perceptible circulation in the bones, yet, that a circulation is
actually existing, is evident, from a liquor oozing out from the ends of
a fractured bone in the living animal; by which a fractured bone again
unites, and this is called the _callus_; and whilst in its liquid state,
resembles the white of an egg, which gradually ossifies, and becomes as
hard as the main substance of the bone.
The number of bones differ somewhat in various subjects; ordinarily they
amount to two hundred and fifty-two: In the head sixty-three; in the
trunk seventy; in the arms and hands sixty; and in the legs and feet
sixty.
As the bones are the support of the animal fabric, I have inserted in
the next page, a catalogue of the human skeleton, which occasionally may
be referred to:
_A Skeleton of the Human Body._
BONES in the HEAD.
The SKULL.
_The Forehead._