SEC. 2. ON THE CHANGES WHICH TAKE PLACE IN 

 A MUSCLE DURING A CONTRACTION. 



The Change in Form. 



§ 52. An ordinary skeletal muscle consists of elementary 

 muscle fibres, bound together in variously arranged bundles by 

 connective tissue which carries blood vessels, nerves and lym- 

 phatics. 



The contraction of a muscle is the contraction of all or some of 

 its elementary fibres, the connective tissue being passive ; hence 

 while those fibres of the muscle which end directly in the tendon, 

 in contracting pull directly on the tendon, those which do not so 

 end pull indirectly on the tendon by means of the connective 

 tissue between the bundles, which connective tissue is continuous 

 with the tendon. 



Each muscle is supplied by one or more branches of nerves 

 which, running in the connective tissue, divide into smaller 

 branches and twigs between the bundles and between the fibres, 

 and eventually end in such a way that every muscular fibre is sup- 

 plied with at least one nerve fibre, which joins the muscular fibre 

 somewhere about the middle between its two ends or sometimes 

 nearer one end, in a special nerve ending called an end-plate. It 

 follows that when a muscular fibre is stimulated by means of a 

 nerve fibre, the nervous impulse travelling down the nerve fibre 

 falls into the muscular fibre not at one end but at about its mid- 

 dle ; it is the middle of the fibre which is affected first by the 

 nervous impulse, and the changes in the muscular substance 

 started in the middle of the muscular fibre travel thence to the 

 t wo ends of the fibre. In an ordinary skeletal muscle however, the 

 fibres and bundles of fibres begin and end at different distances 

 from the ends of the muscle, and the nerve or nerves going to 

 the muscle divide and spread out in the muscle in such a way 

 that the end-plates, in which the individual fibres of the nerve 

 end, are distributed widely over the muscle at very different 



