DEVELOPMENT OF MUSCLE. 101 



which offers no resistance to tlie extension of the osseous trabe- 

 culas and the ingrowth of the medullary papillae. The cartilage- 

 cells again proliferate; and their proliferation, owing to the 

 simultaneous liquefaction and partial reabsorption of the inter- 

 cellular substance, assumes very considerable proportions. Each 

 cell gives rise to from eight to sixteen very large daughter- 

 cells. These are separated only by very thin trabecul?e of basis- 

 substance, and form cylindrical columns, disposed at right angles 

 to the surface of the growing bone. The vascular papilla) of 

 the medulla penetrate into this soft, large-celled tissue as readily 

 as though they were growing upon a free surface ; they 

 break down all partitions ; and it is only where the form and 

 position of the medullary cavity happens to allow it, that one or 

 other of the stouter trabecular of the former matrix is retained 

 as a sort of framework, on which layers of young bone-tissue 

 are deposited. To conclude : here, as in sub-periosteal growth, 

 the bone needs no antecedent condition for its development, 

 beyond the presence of a vascularised embryonic connective 

 tissue, which is everywhere produced upon its confines by the 

 intermediate apparatus of nutrition, whether this bo represented 

 by medullary tissue or by periosteum. I will say no more at 

 present about the growth of bone ; ample opportunities for doing 

 this will be afforded in the chapter on Diseases of the Osseous 

 System. 



§ 80. As regards the growth of the 3IUScular organs, we 

 know that the first muscular fibres, whether smooth or striated, 

 originate everywhere from embryonic cells. Where smooth 

 muscular fibre is needed, the cells are converted into the well- 

 known spindle-shaped or ribbon-like structures, while their 

 nuclei assume the form of elongated cylhiders (staff-shaped 

 nuclei). In the case of striped muscle, the cells, according to 

 KoUiker, increase in length, their nuclei imdergoing repeated 

 fission, until the proper length is reached. (According to other 

 authors, each fibre results from the apposition of several cells.) 

 The striped matter is then differentiated from the protoplasm, 

 and becomes a cylinder whose diameter goes on increasing, 

 while the nuclei are pushed to one side, where they combine with 

 the residual protoplasm to form the muscle-corpuscles. 



The after-growth of striped muscle consists, according to 

 KoUiker J of a simple increase in the length and thickness of the 



