SECT. 86.] 



MUSCULAR SYSTEM. 



l S9 



in many fibres the fibrils do not occupy the whole thickness, 

 but arc deposited peripherally, in form of a tube ; whilst, 

 in the interior of the fibre, there still exists a homogeneous 

 substance as formerly, which uoav appears as a canal inclosed 

 by the fibrils. All the fibres possess a sarcolcmma (b), which, 

 on the addition of acetic acid, and caustic soda, can be de- 

 monstrated as a very delicate membrane, and may occasionally 

 be raised from the fibrils by the imbibition of water. Moreover, 

 as at first, they present nuclei, which are Fig. 73. 



situated upon the sarcolemma, and fre- 

 quently raise it into rounded elevations. 

 These nuclei are actively engaged in the 

 process of multiplication ; they are all vesi- 

 cular, rounded or elongated in shape, with 

 very distinct, simple or double nucleoli, of 

 0-0004'" to o - ooo8'" in diameter, and often 

 with two secondary nuclei in their interior. 

 The nuclei are most frequently arranged in 

 pairs, lying close to each other ; but, often, 

 also, in groups of three, four, or even six, 

 placed alongside, or following each other. 

 From this period to the time of birth, 

 the muscular fibres do not undergo any 

 notable alteration, except an increase in 

 thickness. In the new-born infant, they 

 measure 0-0056'" to 0-0063'" in diameter, 

 are solid, of rounded-polygonal form, and lon- 

 gitudinally and transversely striped, accord- 

 ing to circumstances, as in the adult. Their 

 fibrils may now be very easily isolated, and 

 their nuclei are increased in number. 



From the above statement it may be inferred, that the sarco- 

 lemma of a fully-formed fibre is nothing but the cell-mem- 

 brane of a primitive muscular cell, which, by its excessive growth, 

 lias given origin to a long fibre, and that the nuclei of the latter 

 are the descendants of the original cell-nucleus, which has multi- 

 plied by an endogenous process. The muscular fibrils are the 

 differentiated contents of the original tube, which have become 

 firm. In many cases, it can be demonstrated that they are formed 

 from the sarcolemma inwards ; in other instances, perhaps they are 

 developed at once, in the whole width of the tube. 



The growth of the entire muscle chiefly depends upon the 



Muscular fibres from a hu- 

 man embryo four months old, 

 magnified 350 times. 1. a fibre 

 with a clear, still-unstriped 

 substance, in its interior; 2. a 

 fibre without such a substance, 

 and with indications of trans- 

 verse strife ; «. nuclei ; b. sar- 

 colemma. 



