1865.] Striated Muscular Fibre. 375 



brane by the granular non-striated as compared with the striated portion 

 of the fibre diminishes, so that the latter almost entirely fills the mem- 

 brane, the nuclei lying within the membrane but external to the striated 

 portion, and surrounded by a small amount of the granular matter of the 

 original cell-contents. 



The differentiation of the muscular fibre of the chick commences in the 

 dorsal region, according to the author's observations, after about forty- 

 eight hours of incubation. Here the first appearance is of nucleated oval 

 bodies with well-defined outlines, but much smaller than in the tadpole, 

 which the author regards as cells, though he has been unable to isolate a 

 membrane. These rapidly elongate into fusiform bodies, in which some- 

 times a faint striation becomes apparent. Shortly after the commencement 

 of the third day long fibres appear, apparently from the elongation of the 

 former, which are striated both longitudinally and transversely, and upon 

 them is situated a nucleus, around which is some granular matter (the 

 remains of the original cell-contents), the whole being enclosed by a 

 membrane. 



From the fourth to the fifth day a great multiplication of the nuclei 

 follows within the membrane, and in proportion to this multiplication 

 does the diameter of the fibre, and also of the striated portion, increase. 



The author has observed a similar process in the growing extremities of 

 the sheep and of man, and concludes that the growth of muscular fibre 

 commences in the cells of the embryo by the elongation of the cells and 

 multiplication of their nuclei, attended by a simultaneous fibrillation and 

 striation of their contents. He regards the sarcolemma as resulting from 

 the extension of the wall of the parent cell, but thinks that the adult 

 muscular fibre should not be regarded so much in the light of a single 

 many-nucleated cell, as the result of the fusion of many cells in the act of 

 formation, the separation of which, after the division of their nuclei, has 

 been prevented by the early fibrillation of their contents, a view which ap- 

 proximates somewhat to that held by Schwann, and which is also a mo- 

 dification of the opinion expressed by Kolliker and Remak. 



The development of the muscular fibre of the heart in the chick com- 

 mences, according to the author, after forty-eight hours of incubation, by 

 the appearance of stellate cells, which anastomose with one another in all 

 directions. The processes which these give off increase in thickness, and 

 nuclei appear upon them, probably by multiplication of the nuclei of the 

 original cells. Fibrillation and transverse striation of these processes ap- 

 pear from the third to the fourth day. The structure becomes so complex 

 after this period, that the author has been unable to follow the development 

 further. He has not been able to find any membrane resembling the sar- 

 colernma upon these processes from the stellate cells, though with a power 

 of 1250 linear they may often be seen to have a double outline. He 

 thinks the presence of a sarcolemma may be inferred from the fact that 

 the position of the nuclei in relation to the striated portion is the same as 



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