TYPICAL STRUCTURE OF ORGANS 



35 



cytoplasm of tlie muscle fiber and that, immediately under 

 the sarcolemma, xdiere are numerous characteristic nuclei 

 which are easily brbught into view by suitable treatment. 

 Briefly, then, the muscle fiber is a cell with many nuclei, in 

 whose cytoplasm are found peculiar structures, the myofibrils ; 

 upon superficial examination these myofibrils not only obscure 

 the nuclei but give to the whole fiber the 

 appearance of cross striation. 



8. How far is the structure of glands 

 and muscles typical of all organs? Both 

 the gland and the muscle are thus com- 

 posed of cells. Although differing con- 

 siderably in the two organs, these cells 

 possess certain general and fundamental 

 features in common, for each one contains 

 a nucleus (or nuclei) and surrounding 

 cytoplasm. Is the same thing true of all 

 other organs ? The muscle and the gland 

 are examples of organs which do active 

 work, but some other organs perform 

 purely passive functions. Such are the 

 bones, which do no work themselves, but 

 upon which the work of mechanical motion 

 is done by the muscles ; the tendons, which 

 transmit the pull of muscles ; the ligaments, 

 which limit and sometimes guide the mo- 

 tion of bones; and the connective tissues, 

 which bind together other parts of the body. None of these 

 is a working organ in the sense that a muscle or a gland is 

 a working organ, and we are not surprised to find that their 

 structure departs from that of the muscle and gland in that, 

 while nucleated cells are present in all of them, the great mass 

 of the organ is composed of lifeless matter between the cells. In 

 a tendon this consists of very strong parallel fibers (Fig. 24) ; 

 a ligament shows much the same structure ; a bone consists 



FIG. 26. Part of a 

 muscle fiber 



Specially prepared to 

 bring out th 



