THE MUSCULAR SYSTEM. 255 



as at first, present nuclei lying close upon the sarcolerama, and which 

 frequently cause rounded elevations on the surface of the tube, and may 

 be observed actively engaged in the process of multiplication. They 

 are all vesicular, roundish or elongated, with very distinct, simple or 

 double nucleoli measuring 0-0004-0*0008 of a line, and frequently with 

 two secondary cells in the interior. They are much more numerous 

 than previously, and most frequently disposed in pairs closely approxi- 

 mated ; but often, also, in groups of three or four or even six, either 

 contiguous or arranged serially. From this period to that of birth, no 

 further important change takes place in the muscular fasciculi, except 

 an increase in their size. In the new-born infant they measure 0*0056 

 -0-0063 of a line, are solid, rounded, polygonal, longitudinally or 

 transversely striated, according to circumstances, as in the adult, with 

 very readily isolated fibrils, and no longer any appearance of nuclei. 



From what has been remarked, it is clear that the sarcolemma repre- 

 sents the sum of the membranes of the coalesced cells, and that the nuclei 

 of the youngest fasciculi are the original cell-nuclei, whose descendants 

 are represented in the nuclei of the older fibres, which have multiplied 

 by an endogenous process. The muscular fibrils are the altered contents 

 of the original tubes, become solid ; they appear, demonstrably in many 

 instances, to be formed on the inner surface of the sarcolemma, from 

 without to within, but in other cases probably in the whole of the tube 

 at once. 



The growth of the entire muscle is chiefly to be referred to the in- 

 crease, both longitudinal and in thickness, of the primitive fasciculi ; 

 and the rudiments of all the future primitive fasciculi appear to be formed, 

 probably even as early as the original rudiments of the muscle itself 

 in every case at the middle period of foetal life. In the embryo, at the 

 fourth or fifth month, they are perhaps five times as thick as in one at 

 two months ; in the new-born infant they measure for the most part 

 twice, occasionally even three and four times as much as in the fourth 

 and fifth month, and in the adult their size is perhaps five times greater 

 than in the new-born child. The number of fibrils must necessarily in- 

 crease in proportion to the size of the fasciculus, because, according to 

 Harting, they are but little thicker in the adult than in the foetus. The 

 perimysium is developed, as I find in agreement with Valentin and 

 Schwann, after the type of the common connective tissue, from fusiform, 

 coalesced formative cells. 



The elementary parts of the tendons are, in no case, formed earlier 

 than those of the muscles ; for, in embryos from the eighth to the ninth 

 week, I have never been able to detect a trace of them, although at this 

 time the muscular fibres are 'quite distinct. It is not till the third or 

 fourth month, when, moreover, they become distinctly visible to the 

 naked eye, that their elementary constituents can be made out, at this 

 time presenting the appearance of long parallel bands with elongated 



