Human physiology : designed for colleges and the higher classes in schools and for general reading . Muscles made up of cells. Their contraction and relaxation. basement membrane, and upon these, as in the case of themucous coat of the alimentary canal, lie pavement cells. Thesecells, constituting the cuticle or scarf-skin, are much morenumerous than in the alimentary canal. There are manylayers of them. The outer cells dry by exposure to the air,and become scales. As these are rubbed off, the cells belowtake their places ; and there is a constant supply of fresh cellsfrom the basement membran
Human physiology : designed for colleges and the higher classes in schools and for general reading . Muscles made up of cells. Their contraction and relaxation. basement membrane, and upon these, as in the case of themucous coat of the alimentary canal, lie pavement cells. Thesecells, constituting the cuticle or scarf-skin, are much morenumerous than in the alimentary canal. There are manylayers of them. The outer cells dry by exposure to the air,and become scales. As these are rubbed off, the cells belowtake their places ; and there is a constant supply of fresh cellsfrom the basement membrane. 203. There are some cells which are devoted entirely to theproduction of motion, for an ordinary muscle is composed ofgreat numbers of chains of cells included in sheaths bound to-gether. A muscle appears to the naked eye to be made up offibres. Each one of these fibres is found by the miscroscope tobe composed of from 500 to 800 fibrillce, or minute each of these fibrillse is a series or chain of cells. In , a, is represented a fibre as seen under the microscope, FIG. 64. 6. FIBRE OF A MUSCLE. showing the fibrillse of which it is com-posed. They are separated at the brokenend by the violence in tearing the b, you see one of the fibrillse very highlymagnified, showing that it is a chain ofcells. In the diagram, Fig. 65, is repre-sented the condition of a fibrilla in thetwo states of contraction and a it is relaxed. In b it is contracted,the cells being shortened, and at the sametime widened. And as all the cells in themuscle are thus widened when the musclecontracts, we see the cause of the wellknown swelling out of muscles when theyare in action. That you may form someidea of the size of these cells in muscles, Iwill state that in the space of the squareof a tenth part of an inch, thus, there are over 100,000 of these cells. Q When FIG. 65. muscular fibril; a relaxed ; b contracted. CELL-LIFE. 131 Hoofs, horns, nails, and teeth made h
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