THE MTJSCULAK SYSTEM. 401 



the intermediary plexus passes to enter a muscle-fibre, its primitive 

 sheath becomes continuous with the sarcolemma, and the axis-cylinder 

 forms a network of its fibrils on the surface of the fibre. This network 

 lies imbedded in a flattened granular mass containing nuclei of several 

 kinds; this is the material end-plate (Fig. 281). In batrachia, besides 

 end-plates, there is another way in which the nerves end in the muscle- 

 fibres, viz., by rounded extremities, to which oblong nuclei are attached. 



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

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

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



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

 formed by the coalescence oi several cells, but recently it has been proved, 

 that each fibre is formed from a single cell, the process involving an enor- 

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

 differentiation of the cell-contents. This view differs but little from the 

 other, that the muscular fibres 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 devel- 

 oped 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 infiltration of the tissue and degeneration of the fibres. 



II. THE CHEMICAL COMPOSITION OF MUSCLE. 



A. Proteids. The principal substance which can be extracted from 

 muscle, when examined after death, is a proteid body, called Myosin. 

 This body appears to bear the same relation to the living muscle, as 

 fibrin does to the living blood, since the coagulation of muscle after death 

 is due to the formation of myosin. Thus if coagulation be delayed in 

 muscles removed immediately from recently killed animals, by subjecting 

 them to a temperature below C., it is possible to obtain from them by 

 expression a viscid fluid of slightly alkaline reaction, called muscle plasma 

 (Kuhne,Halliburton). And muscle plasma, if exposed to the ordinary 

 temperature of the air (and more quickly at 37-40 C.), undergoes coag- 

 ulation much in the same way as does blood plasma, separated from the 

 blood by the action of a low temperature, under similar circumstances. 

 The appearances presented by the fluid during the process are also very 

 similar to the phenomena of blood-clotting, viz., that first of all an in- 

 creased viscidity on the surface of the fluid, and at the sides of the con- 

 taining vessel, appears, which gradually extends throughout the entire 

 mass, until a fine transparent clot is obtained. In the course of some 

 hours the clot begins to contract, and to squeeze out of its meshes a fluid 



