STRIATED MUSCULAR FIBRE. 



401 



Fig. 255. 



Striated muscular fibre is not regenerated] and wounds in mus- 

 cles heal simply with a tendinous callus. t 



The development of the accessory parts of muscles (tendons, &c.) 

 is included under that of the muscles as distinct organs (Section II.). 



The Function of Striated Muscular Fibre. 



Striated, like smooth muscular fibre, is distinguished by the vital 

 property of contractility but, unlike the latter, the former may be 

 made to contract voluntarily. The direct result of the contraction 

 of the striated fibres in a muscle, is a 

 shortening of it; which approximates its 

 two extremities, and at the same time 

 produces motion of one of the parts 

 (usually a bone) to which it is attached. 

 But we have here to speak of the con- 

 traction of single fibres only. 



If a striated fibre be observed while 

 contracting, it is seen to become shorter 

 and thicker; the strias approach each 

 other (Fig. 255) ; and sometimes the 

 muscular fluid, forced out from between 

 the fibrillse, causes the myolemma to 

 project at points, forming bullas, as seen 

 in Fig. 256. It is scarcely profitable to 



inquire what causes the shortening of traction seen moving along one marsin 

 the fibre, by the approximation of its 

 disks, since it is a vital act; and the 

 merely chemical explanation suggested 

 by Liebig is altogether unsatisfactory. 

 But that the musculine alone is endowed with the property of con- 

 tractility, is sufficiently certain. 



Fig. 256. 



Stages of contraction seen in muscu- 

 lar fibre of the skate. The uppermost 

 figure shows its state previous to the 

 commencement of active contraction, 

 a, a, a. Successive "waves" of con- 



of the fibre ; marked by a bulging of 

 the margin, an approximation of the 

 transverse stripes, and a consequent 

 darkening of the spots, b, b, b. Simi- 

 lar "waves" still moving along the 

 fibre, but engaging its whole thickness. 



Muscular fibre of Dytiscus, showing the contracted state in the centre, the stria approximated, the 

 breadth of the fibre increased, and the myolemma raised in bull* on its surface. 



It is, however, the fact that ordinarily (and perhaps always) the 

 immediate stimulant to contraction of the striated fibres is an influ- 

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