Usually situated at the extremities of the fleshy fascia, they
sometimes however occupy the middle, as we see in the digastric
muscle; they are almost always found at the most moveable extremity,
that which serves for support having aponeuroses for insertion, as we
see especially on the fore-arm and the leg, of which all the muscles
inserted above by broad osseous or aponeurotic surfaces, terminate
below by a more or less slender tendon. From this arrangement result,
1st, little thickness at the extremity of the limbs, and consequently
facility in their motions; 2d, great resistance to external pressures
very frequent in this place, the fibrous texture being, as we have
said, very resisting; 3d, the concentration of the whole effort of a
muscle oftentimes very thick upon a very narrow osseous surface, and
for the same reason the extent and force of the motions of the bone.
The tendinous forms are usually round, no doubt because they are those
in which, with the least size the greatest quantity of matter enters.
Sometimes however as in the tendons of the extensors of the leg and the
fore-arm, they are flat.
Sometimes bifurcated or divided into many secondary elongations, the
tendons are inserted into the bones, or receive fleshy fibres in two or
many different points. All are covered by a loose texture which allows
them to slide easily upon each other, or upon the neighbouring parts.
Sometimes this texture is wanting, and then the synovial capsules
surround them to favour their motions. Their extremity, in which the
fleshy fibres are fixed, receives these fibres differently. Sometimes
it is to one side only that they are attached; hence the semi-penniform
muscles; at other times it is to both sides at the same time; this
constitutes the penniform. Frequently the tendon is buried so deep in
them, that it cannot be laid bare, but by dividing them longitudinally.
The adhesion is very great between the fleshy and tendinous fibre.
Yet by macerating them a long time or subjecting them to ebullition,
they gradually separate from each other. I have observed that in young
subjects the union was much less intimate; thus by scraping at this age
the tendon with a scalpel, we remove from it the muscle, without its
ever appearing again; the polish is almost the same where the fibres
are inserted, as where they are naturally wanting. The extremity of the
tendon fixed to the bone, intermixes with the periosteum as it usually
expands; so that it is with this membrane, and not with the bone
itself, that the tendon makes part, because in fact it is the membrane
which is of the same nature; thus if it finds an analogous membrane,
it fixes to it equally, as we see in the insertion of the straight and
oblique muscles in the sclerotica, of the ischio and bulbo-cavernous
ones in the membrane of the corpus cavernosum. In general the tendons
never unite but to fibrous membranes; the serous, the mucous, every
organ in a word, foreign to the fibrous system, is also heterogeneous
to them.