84 



THE HUMAN BODY 



fiber consists of a certain amount of muscle substance, the muscle 

 plasma, inclosed in a transparent connective tissue sheath, the sar- 

 colemma. This latter structure serves not only to hold the semi- 

 fluid muscle plasma in place, but also to transit the pull of the 

 contracting fiber to the point of attachment of the muscle. The 

 most striking characteristic of a fiber's appearance is the series 

 of alternating light and dim transverse bands of nearly equal 

 width with which it is marked, and from which its designation as 

 striated muscle is derived (Fig. 42). Under the high power of the 

 microscope the muscle plasma is seen to be made up of a number 



FIG. 42. A, Portion of a Human muscle fiber. B, Separated bundles of sar- 

 costyles, d, single sarcostyle. x 800. (Sharpey.) 



of longitudinal fibrils, the sarcostyles, surrounded by a homogene- 

 ous medium, the sarcoplasm. 



Not all histologists are agreed as to the details of structure of 

 the sarcostyles; they are so small that only the highest powers of 

 the microscope can be used in studying them; they occur in ordi- 

 nary muscle surrounded always by sarcoplasm and in company 

 with many others. These circumstances combine to present to 

 the eye of the observer a more or less distorted picture. It is no 

 wonder, therefore, that differences of opinion as to the real struc- 

 ture of the sarcostyles have arisen. 



