After general growth is finished in length, our organs then increase
in thickness; and it is especially in the muscles that this phenomenon
is remarkable. To the slender and delicate body and round forms of the
youth and young man, succeeds a large, strong and thick body with well
developed forms. The muscles can be traced through the integuments,
eminences and depressions are observed in them; different depressed
lines serve as limits to various prominent ones. The animal muscular
system is then more prominent in a state of repose, than it is in youth
in its greatest motions. Painters and sculptors have studied more than
anatomists the different degrees of the development of the muscles.
The period when the hairs grow, when the genital organs begin to become
active, is principally that in which the muscles begin to become
prominent in man. In woman, this last period does not present a similar
phenomenon; the muscles preserve the original roundness, they scarcely
ever lose it. In this sex, the roundness of the limbs, their agreeable
forms, make a contrast with the kind of rudeness of those of man.
The increase in thickness in the muscles appears to be much more
in the fleshy than the tendinous portion, and especially than the
aponeurotic. The intermuscular aponeuroses principally do not appear
to grow in proportion to the fibres that are inserted into them; so
that these make a prominence, and at the place of the aponeurosis there
is a depression. This is what we see very well in muscles cut for
their insertions by many of these fibrous expansions, in the deltoid
in particular. Not only the prominence through the skin of the whole
of the muscle, makes the depressions evident that separate it from
the others, but each fleshy bundle has a prominence which a groove
separates; this, it is true, is only distinguishable upon thin subjects.
As the muscle grows in thickness, it increases in density. It becomes
firmer and more resisting. If we place for comparison the hand upon
two similar muscles of an adult and an infant, whilst they are in
contraction, we feel a sensible difference in their hardness. Weights
suspended for comparison to the muscles of the two ages, taken in the
dead bodies, prove the different degree of their resistance. The
muscular texture of adults yields more slowly to all re-agents.
The colour of the muscles continues to be red in the adult; but in
general, and all things being equal in respect to the causes that make
this colour vary, it begins to become of a less bright red after the
thirtieth year. It is usually in the last years of growth, and even
from the tenth to the twentieth, that the colour is the most brilliant.
In the adult this colour exhibits a very remarkable phenomenon. All men
have their muscles red, but hardly two have the same shade. Those who
have opened many dead bodies are easily convinced of this; a residence
at the dissecting rooms proves this assertion. A thousand causes have
an influence upon this colour; the temperament is the principal. The
external appearance of the muscles without the skin indicates by
their shades of colour the temperament, as well as the integuments
do. Diseases make this colour vary wonderfully. All those that have
a chronic progress alter it remarkably; it then becomes pale, dull,
&c. Dropsies whiten it, when they are of long standing. In general,
every thing that has upon the powers of life a slow and debilitating
influence, diminishes the brightness of it. Acute diseases, whatever
may be their nature, change it but little. Fevers with the greatest
prostration, if they suddenly produce death, leave it untouched,
because this colour can only change by nutrition; now as this function
is slow in its phenomena, it is but little affected by acute diseases;
it is only at the end of some time that it feels the affections
reigning in the economy.
I would observe that the varieties of colour that are seen in the
muscles of adults, even in the healthy state, distinguish them
especially from those of the fœtus, which have in general an uniform
paleness. This difference is owing to the fact, that in the first
age, we are not subject to the action of the numerous agents which
modify, in an infinitely variable manner in the after ages, the great
functions, and of course nutrition which is the end of them. It is in
these varieties of colour of the muscular system of the adult, that
we clearly distinguish that the blood circulating in the arteries is
wholly foreign to it; in fact it is uniform, and never partakes of
those varieties of colour whatever they may be.
Many circumstances in the adult make the muscular nutrition vary;
motion is the principal. The man who passes his life at rest is
remarkable for the small prominence of his muscles, especially if we
compare this prominence with that of the muscles of a man who takes
great exercise. Not only general motion exhibits this phenomenon,
but also local motion, as we see in the arms of bakers, the legs of
dancers, the backs of porters, &c.