J72 



STRUCTURE OF MUSCLE. 



Fig. 104.* 



ranged side by side, constitute the bright band ; while the transparent 

 cells of the single fibril are the shaded stria 4>f the fibre. 



When the ultimate fibril is very much stretched, the two highly- refrac- 

 tive cells appear each to be double, while the transparent space is evidently 

 composed of four cells. 



The ultimate fibre of organic life (Fig. 104, 4, 5) is a simple homoge- 

 neous filament, much smaller than the fibre of animal life, flat, and with- 

 out transverse markings. Besides these characters, there may generally 

 be seen a dark line or several dark points in its interior, and not unfre- 

 quently the entire fibre appears enlarged at irregular distances. These 

 appearances are due to the presence of the unobliterated nuclei of cells 

 from which the fibre was originally developed. The fibres of organic life 

 are collected into fasciculi of various size, and are held together by dark 

 nuclear fibres, similar to those which bind the fasciculi of fibrous tissue 

 (p. 134.) 



The development of muscular fibre is 

 effected by means of the formation of 

 nucleated cells out of an original blas- 

 tema, and the conversion of those cells, 

 by a process already described (p. 46), 

 into the tubuli of ultimate fibres, while 

 their contents, by a subsequent deve- 

 lopmental action, are transferred into 

 ultimate fibrils. According to this view 

 the cell membranes constitute the myo- 



T lemma, and the contents of the cell are 

 a blastema out of which new cells are 

 formed. 



The disposition of these latter cells, in the production of fibrillse, is 

 probably much more simple than has hitherto been conceived. In the 

 muscular fibre of organic life, the process would seem to stop short of the 

 formation of fibrillaB, the cells being accumulated without apparent order. 

 The corpuscles, observed by Mr. Bowman, in fetal muscle (fig. 102), and 

 the nodosities of organic fibre, are obviously undeveloped cells and nuclei. 

 Muscles are divided into two great classes, voluntary and involuntary, 

 to which may be added, as an intermediate and connecting link, the 

 muscle of the vascular system, the heart. 



The voluntary , or system of animal life, is developed from the external 

 or serous layer of the germinal membrane, and comprehends the whole 

 of the muscles of the limbs and of the trunk. The involuntary, or organic 

 system, is developed from the internal or mucous layer, and constitutes 

 the thin muscular structure of the intestinal canal, bladder, and internal 



* 1. A muscular fibre of animal life enclosed in its myolemma; the transverse and 

 longitudinal striae are seen. 



2. An ultimate fibril of muscular fibre of animal life, according to Mr. Bowman. 



3 A muscular fibre of animal life, similar to 1, but more highly magnified. Its myo- 

 lemma is so thin and transparent, as to permit the ultimate fibrils to be seen through 

 The true nature of the longitudinal striae is seen in this fibre, as well as the mode of 

 formation of the transverse striae. 



4. A muscuiar fibre of organic life, from the urinary bladder, magnified 600 times, 

 linear measure. Two of the nuclei are seen. 



f>. A muscular fibre of organic life, from the stomach, magnified 600 times. The 

 diameter of this and of the preceding fibre, midway between the nuclei, was JT^J 

 of an inch. 



