214 THE ORGANS 



In Fig. 129 the individual muscle fibrillae are seen passing over into 

 tendon librillai with no line of demarcation. In Fig. 130 a similar 

 continuity is shown except that groups of muscle fibrilhe are seen to 

 be continuous with groups of tendon fibrillae. Both sarcoplasm, 

 which appears somewhat augmented at this point, and sarcolemmae, 

 extend between the tendon bundles beyond the line of cross muscle 

 striations. Along the line of union of muscle and tendon the muscle 

 nuclei are more numerous than elsewhere (Fig. 128, b), and it has 

 been suggested that there is here a zone of indifferent or formative 



,. Krause line 

 >?■•'•' , Dark band 



:l t^ '1 li ill »••• 



Transition zone ... - ■'■ 



Tendon fibrils 



Nucleus 



Fig. I2g. — Longitudinal Section through Muscle-tendon Junction. Human Intercostal. 

 X750. Only part of a fibre is shown, without sarcolemma. (Stohr.) 



tissue which is capable of developing on the one hand into muscle, 

 on the other into the connective tissue of tendon. 



Growth of muscle takes place mainly at the ends of the fibres 

 where the nuclei are most numerous. In addition to the growth 

 incident to increase in size of the individual or of the particular 

 muscle, there is a constant wearing out of muscle fibres and their 

 replacement by new fibres. This is accomplished as follows: The 

 muscle fibre first break? up into a number of segments (sarcostyles), 

 some of which contain nuclei while others are non-nucleated. The 

 sarcostyles next divide into smaller fragments, and finally completely 

 disintegrate. This is followed by a process of absorption and com- 

 plete disappearance of the fibre. From the free sarcoplasm new 



