515 



mass of free nuclei. When isolated, these fibres are seen to be attached 

 to one or more of the nuclei by a variable quantity of blastema. 

 Sometimes a single nucleus with conical processes of delicate granular 

 substance is first enclosed by fine fibrillse or lateral bands, which 

 present somewhat the appearance of a cell-wall, so that the object 

 has a certain resemblance to a nucleated fusiform cell with a fibre 

 originating from one of its extremities. Sometimes several nuclei are 

 cemented in a group around a fibre, and become subsequently covered 

 by other fibres of the same kind ; and sometimes they lie in linear 

 series, either at some distance apart, or overlying each other to a cer- 

 tain extent like a series of coins. The lateral bands or fibres enclosing 

 the nuclei extend around them as a tubular investment, which grows 

 in thickness from without, but not always uniformly on all sides. 

 In the process of longitudinal growth, the nuclei multiply by subdi- 

 vision, become generally more oval, and approach nearer to the sur- 

 face of the fibre, which at the same time contracts in diameter. The 

 subsequent changes they pass through are nearly similar to those 

 which occur in the chick. 



In man the development of muscular fibre proceeds on the same 

 general plan as in birds and mammalia, but differs from that of both 

 in certain unimportant particulars. In the early stages there is no 

 distinct appearance of those oval, cylindrical, and irregular masses 

 observable in the chick on the seventh day of incubation and in the 

 mammal at a corresponding period. In this respect there is a greater 

 resemblance between the two latter classes than between man and 

 either. In the human foetus, from about half to three-quarters of an 

 inch in length, the first stage of development may be seen to com- 

 mence by the formation of fine lateral bands or fibrillse along one or 

 both sides of one nucleus or more. "When, however, there are more 

 nuclei than one enclosed by the same lateral bands, they are always 

 disposed in linear succession, with their longer axes in th'e direction 

 of the fibre, and never occur in irregular groups, as is sometimes the 

 case both in birds and mammals, in which, consequently, the same 

 kind of fibres are often broader at first. Thus formed, they lie side 

 by side in bundles of different sizes, to which new fibres or new 

 fibrillse are being continually added by a renewed process of develop- 

 ment. Every fibre is the rudiment of several fibrillse. At this 

 period each lateral band constitutes a single fibrilla, which is often 



