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HAND-BOOK OF PHYSIOLOGY. 



meshes around the fibres on the outside of the sarcolemma. No vessels 

 penetrate the sarcolemma to enter the interior of the fibre (Fig. 270). 

 Nerves also are supplied freely to muscles (pp. 76, 80, Vol. II. ) ; the volun- 

 tary muscles receiving chiefly nerves from the cerebro-spinal system, and 

 the unstriped muscles from the sympathetic or ganglionic system. 



FIG. 274. Muscular fibre cells from the heart. (E. A. Schafer.) 



Development. (1.) Unstriped. The cells of unstriped muscle arc 

 derived directly from embryonic cells, by an elongation of the cell, and 

 its nucleus; the latter changing from a vascular to a rod shape. 



(2.) Striped. Formerly it was supposed that striated fibres are formed 

 by the coalescence of several cells, but recently it has been proved, that 

 each fibre is formed from a single cell, the process involving an enormous 

 increase in size, a multiplication of the nucleus by fission, and a differen- 

 tiation of the cell-contents (Remak, Wilson Fox). This view differs but 

 little from that previously taken by Savory, that the muscular fibre is 

 produced, not by multiplication of cells, but by arrangement of nuclei in 

 a growing mass of protoplasm (answering to the cell in the theory just 

 referred to), which becomes gradually differentiated so as to assume the 

 characters of a fully developed muscular fibre. 



Growth of Muscle. The growth of muscles, both striated and non- 

 striated, is the result of an increase both in the number and size of the 

 individual elements. 



In the pregnant uterus the fibre-cells may become enlarged to ten 

 times their original length. In involution of the uterus after parturition 

 the reverse changes occur, accompanied generally by some fatty infil- 

 tration of the tissue and degeneration of the fibres. 



PHYSIOLOGY OF MUSCLE. 

 Muscle may exist in three different conditions: rest, activity, and rigor. 



