CHAP, ii.] THE CONTRACTILE TISSUES. 85 



the middle of the muscle which do not reach to either end. In 

 such case the connective tissue in which the sarcolemma ends 

 is continuous with the connective tissue which, running between 

 the fibres and between the bundles, binds the fibres into small 

 bundles, and the smaller bundles into larger bundles. 



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. 



The blood vessels run in the connective tissue between the 

 bundles and between the fibres, and the capillaries form more or 

 less rectangular networks immediately outside the sarcolemma. 

 Lymphatic vessels also run in the connective tissue, in the lymph 

 spaces of which they begin. Each muscular fibre is thus surrounded 

 by lymph spaces and capillary blood vessels, but the active muscular 

 substance of the fibre is separated from these by the sarcolemma ; 

 hence the interchange between the blood and the muscular sub- 

 stance is carried on backwards and forwards through the capillary 

 wall, through some of the lymph spaces, and through the sarco- 

 lemma. 



Each muscle is supplied by one or more branches of nerves 

 composed of medullated fibres, with a certain proportion of non- 

 medullated fibres. These branches running in the connective 

 tissue divide into smaller branches and twigs between the bundles 

 and fibres. Some of the nerve fibres are distributed to the blood 

 vessels, and others end in a manner of which we shall speak later 

 on in treating of muscular sensations ; but by far the greater part 

 of the medullated fibres end in the muscular fibres, the arrange- 

 ment being such that every muscular fibre is supplied with at 

 least one medullated 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, of which we shall 

 presently have to speak, called an end plate. The nerve fibres 

 thus destined to end in the muscular fibres divide as they enter 

 the muscle, so that what, as it enters the muscle is a single 

 nerve fibre, may, by dividing, end as several nerve fibres in several 

 muscular fibres. Sometimes two nerve fibres join one muscular 

 fibre, but in this case the end plate of each nerve fibre is still at 

 some distance from the end of the muscular fibre. 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 middle ; 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 two ends of the fibre. 



