SEC. 2. ON THE CHANGES WHICH TAKE PLACE IN 

 A MUSCLE DURING A CONTRACTION. 



The Change in Form. 



52. Gross structure of muscle. An ordinary skeletal muscle 

 consists of elementary muscle fibres, bound together in variously 

 arranged bundles by connective tissue which carries blood vessels, 

 nerves and lymphatics. The same connective tissue besides sup- 

 plying a more or less distinct wrapping for the whole muscle forms 

 the two ends of the muscle, being here sometimes scanty, as where 

 the muscle appears to be directly attached to a bone, and a small 

 amount only of connective tissue joins the muscular fibres to the 

 periosteum, sometimes abundant, as when the connective tissue 

 in which the muscular fibres immediately end is prolonged into 

 a tendon. 



Each elementary fibre, which varies even in the mammal in 

 length and breadth (in the frog the dimensions vary very widely) 

 but may be said on an average to be 30 or 40 mm. in length 

 and 20yu- to 30/z- in breadth, consists of an elastic homogeneous or 

 faintly fibrillated sheath of peculiar nature, the sarcolemma, which 

 embraces and forms an envelope for the striated muscular substance 

 within. Each fibre, cylindrical in form, giving a more or less 

 circular outline in transverse section, generally tapers off at each 

 end in a conical form. 



At each end of the fibre the sarcolemma, to which in life the 

 muscular substance is adherent, becomes continuous with fibrillse 

 of connective tissue, the nature and properties of which we shall 

 study in a succeeding chapter. When the end of the fibre lies at 

 the end of the muscle, these connective tissue fibrilla3 pass directly 

 into the tendon (or into the periosteum, &c.), and in some cases of 

 small muscles which are no longer than their constituent fibres, 

 each fibre may thus join at each end of itself, by means of its 

 sarcolemma, the tendon or other ending of the muscle. In a very 

 large number of muscles however the muscle is far longer than 



