MUSCLES. 55 



Of tke diverse theories put forth as to the mode of 

 development of muscular tissue, we shall notice only 

 that which seems to us most in conformity with ascer- 

 tained facts. 



Muscular tissue is derived originally, like all the 

 other tissues, from the primordial cells of the embryo, 

 which, at first, everywhere the same, undergo a spe- 

 cial metamorphosis in order to form each and every 

 histological element. 



The embryonic cells which are about to form mus- 

 cular fibres at first increase in length, and then, 

 coming in contact with each other by their narrowing 

 extremities, finish by uniting together. Afterwards, 

 the partitions formed by these lines of union disap- 

 pear, and we have, as a result of the process, tubes 

 of structureless membrane presenting constrictions 

 (which mark the line of fusion of the original cells), 

 and intervening expansions, each of which contains a 

 nucleus (PL IX. fig. IV. 1, 2, 3). At this period 

 their diameter varies from ToVoth to 4<rth of a line. 

 During the process of transformation the contents of 

 the cells, at first hyaline, become granular, and the 

 granules, which bear some resemblance to oil-globules, 

 assume a regular arrangement either in longitudinal or 

 transverse rows (PL IX. fig. IV. 4, 5, 6). Still later, 

 the muscular fibre, thus formed, increases in thick 

 ness, assumes a cylindrical shape, and its several cha- 

 racteristic features become more and more obvious ; 

 the division of its interior into fibrillse is noticed, and 

 also the appearance of a large quantity of nuclei, which 

 take their origin by endogenous multiplication. If, at 

 this moment, the extremity of a fibre is examined on 



