STRUCTURE OF MUSCLE. 



441 



FIG. 179. 



in transverse section. When freed from all pressure or traction 

 they become cylindrical and the 

 transverse striation of the contrac- 

 tile substance appears regular, and 

 is easily recognized. 



Each fibre consists of a delicate 

 case of thin, elastic, homogeneous 

 membrane, forming a sheath called 

 sarcolemma, within which the es- 

 sential contractile substance is in- 

 closed. The soft contractile sub- 

 stance completely fills and distends 

 the elastic sarcolemma, so that when 

 the latter is broken its contents 

 bulge out or escape. After death, 

 particularly if preserved in weak 

 acid (HC1), the striation becomes 

 more marked, and the dead and 

 now rigid contractile substance can 

 be easily broken up into transverse 

 plates or disks. 



Besides the transverse striation a 

 longitudinal marking can be seen in 

 the muscle fibre which indicates the 

 subdivision of the contractile sub- 

 stance into thin threads called 

 primitive fibrillse. Each primitive 

 fibril shows a transverse marking, 

 corresponding with the transverse 

 striation, which divides the fibrils 

 into short blocks called sarcous, or 

 muscle elements. These markings, 

 as well as the transverse striations of 



Two fibres of striated muscle, 

 in which the contractile sub- 



the muscle fibre in general, depend stance (m} has been ru P tured 



,. l .. and separated from the sarco- 



on different parts of the contractile ]emma (a) and ( 8);(p) 8pace 

 substance having different powers 



37 



under sarcolemma. (Kanvier.) 



