CHARACTERS OF MUSCLE.
While the bones form the framework of the body, the main bulk of the substance which clothes them consists of muscular tissue, what is termed flesh, which forms about two-fifths of the entire weight of the body. Muscular tissue does not cover and surround the bones in con tinuous sheets, but is collected into masses, varying in size and length, and arranged in different ways. Each separate mass is called a muscle, and is divided off from its neighbours by partitions of connective tissue. Each muscle is supplied with blood-vessels, and with other vessels called lymphatics and nerves, which also have their sheaths of connective tissue ; and vessels and nerves also run between muscles on their way to other parts. Over the muscles is a continuous sheet of fibrous tissue, having embedded in its substance a large number of fat cells. It is called fascia, and it not only covers over all the muscles, but tills up to some extent inequalities of surface, and gives a rounded and regular appearance. Finally, outside of all is the skin. So that if a limb were to be examined, say an arm, after the outer covering of the skin had been removed, the fascia, presenting a fatty appearance, would appear. When it in turn had been stripped off, the various muscles would be revealed, inclosed in their sheaths and separable from one another. On pushing some of them aside vessels of various size and nerves would be visible, and not till the muscles had been stripped off would the bones be uncovered.
Of course in some places, and particularly in the neighbourhood of joints, the bones come very near the surface, being covered by little else than fascia and skin.
The muscular tissue forming the masses is red in appearance, and it is therefore called red muscle. But there is another kind, called white muscle, found in the walls of blood vessels, in the coats of the stomach, bowels, and bladder, in the walls of the air-tubes of the lungs, and elsewhere. Both kinds of muscle are the active agents in motion ; but the movement caused by red muscle, for in stance the motions of our limbs in walking, which are due to contractions of the muscles of the leg, is a movement controlled by our will, while the white muscle exists in organs also capable of contractions, but contractions quite independent of our will. For this reason the red muscle is also called voluntary muscle, and the white involuntary muscle. Red muscle presents, when viewed under the microscope, a striped or striated appearance, while the white is smooth and regular ; the one is there fore called striped or striated muscle, and the other unstriped, non - striated, or smooth muscle. A third variety of muscle is found in the heart (p. 297).