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PROCEEDINGS OF SOCIETIES. 



Royal Society. 



Mr. Savory, " On the Development of Muscular Fibre in Mam- 

 malia." 



The author's observations were made chiefly upon foetal pigs ; but 

 they have been confirmed by repeated examinations of the embryos 

 of many other animals, and of the human foetus. 



If a portion of tissue immediately beneath the surface from the 

 dorsal region of a foetal pig, from one to two inches in length, be 

 examined microscopically, there will be seen, besides blood-cor- 

 puscles in various stages of development, nucleated cells and free 

 nuclei or cytoblasts scattered through a clear and structureless 

 blastema in great abundance. These cytoblasts vary in shape and 

 size ; the smaller ones, which are by far the most numerons, being 

 generally round, and the larger ones n:iore or less oval. Their out- 

 line is distinct and well defined, and one or two nucleoli may be 

 seen in their interior as small, bright, highly-refracting spots. The 

 rest of their substance is either uniformly nebulous or faintly 

 granular. 



The first stage in the development of striated muscular fibre con- 

 sists in the aggregation and adhesion of the cytoblasts, and their 

 investment by blastema so as to form elongated masses. In these 

 clusters the nuclei have, at first, no regular arrangement. Almost, 

 if not quite as soon as the cytoblasts are tiuis aggregated, they 

 become invested by the blastema, and tliis substance at the same 

 time appears to be much condensed, so that many^ of the nuclei 

 become obscured. 



These nuclei, thus aggregated and invested, next assume a much 

 more regular position. They fall into a single row with remarkable 

 uniformity^, and the surrounding substance at the same time grows 

 clear and more transparent, and is arranged in the form of two 

 bands bordering the fibre and bounding the extremities of the nuclei, 

 so that now they become distinctly visible. They are oval, and 

 form a single row in the centre of the fibre, closely packed together 

 side by side, their long axes lying transversely, and their extremiiies 

 bounded on either side by a thin, clear, pellucid border of apparently 

 homogeneous substance. 



It is to be observed how closely the muscular fibres of mammalia 

 at this period of their development resemble their permanent form 

 in many insects. 



The fibres next increase in length and the nuclei separate. Small 

 intervals appear between them. The spaces rapidly widen, until at 

 last the nuclei lie at a very considerable distance apart. At the 

 same time the fibre strikingly decreases in diameter ; for as the 

 nuclei separate, the lateral bands fall in and ultimately coalesce. 



