The People's Common Sense Medical Adviser in Plain English: or, Medicine Simplified, 54th ed., One Million, Six Hundred; and Fifty Thousand — John Stuart Mill — John Shaqi
The People's Common Sense Medical Adviser in Plain English: or, Medicine Simplified, 54th ed., One Million, Six Hundred; and Fifty Thousand
John Stuart Mill · en
THE DIAPHRAGM, or midriff, is the muscular division between the thorax
and the abdomen. It has been compared to an inverted basin, the
concavity of which is directed toward the abdomen. The muscles receive
their nourishment from the numerous blood-vessels which penetrate their
tissues. The voluntary muscles are abundantly supplied with nerves,
while the involuntary are not so numerously furnished. The color of the
muscles is chiefly due to the blood which they contain. They vary in
size according to their respective functions. For example, the functions
of the heart require large and powerful muscles, and those of the eye,
small and delicate ones. There are between four hundred and sixty and
five hundred muscles in the human body.
[Illustration: Fig. 24.
A representation of the superficial layer of muscles on the anterior
portion of the body.]
[Illustration: Fig. 25.
A representation of the superficial layer of muscles on the posterior
portion of the body.]
Very rarely is motion produced by the action of a single muscle, but by
the harmonious action of several. There is infinite variety in the
arrangement of the muscles, each being adapted to its purpose, in
strength, tenacity, or elasticity. While some involuntarily respond to
the wants of organic life, others obey, with mechanical precision, the
edicts of the will. The peculiar characteristic of the muscles is their
contractility; for example, when the tip of the finger is placed in the
ear, an incessant vibration, due to the contraction of the muscles of
the ear, can be heard. When the muscles contract, they become shorter;
but what is lost in length is gained in breadth and thickness, so that
their actual volume remains the same. Muscles alternately contract and
relax, and thus act upon the bones. The economy of muscular power thus
displayed is truly remarkable. In easy and graceful walking, the forward
motion of the limbs is not altogether due to the exercise of muscular
power, but partly to the force of gravity, and only a slight assistance
of the muscles is required to elevate the leg sufficiently to allow it
to oscillate.