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 con- 

 nective 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 

 20/u, to 30yu- 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 fibrillge 

 of connective tissue. When the end of the fibre lies at the end 

 of the muscle, these connective tissue fibrillae 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 

 any of its fibres, and there may even be whole bundles of fibres in 



