Musculab Tissue 



33 



Lymph and blood vessels and nerves are found in the internal perimysium. 

 The nerve terminals are either on the surface of the ordinary muscle fibers, 

 or on fibers enclosed in muscle spindles. 



The individual fibrils are composed of two kinds of substance, arranged 

 in regular alternation. The isotropic substance singly refracts light, and 

 does not readily stain in the preparation of sections. The anisotropic 

 substance is doubly refractive, and stains deeply. The arrangement of 

 these two substances in the fibrils of a single cell is practically parallel, 

 and this gives the ' striped ' appearance to the fibers. The functions of 

 these two substances is not understood, but there are several tentative 

 theories as to the way in which they behave in the process of contraction. 



Muscle nucleus 

 Transition zone 



Sarcolemma. 



Sarcoplasm. 



Tendon fiber bundles. 



Tendon nucleus. 



Fig. 22. Junction of striped muscle and tendon in frog. 

 (Bailey, Histology, after Stohr.) 



Magnified 750 diameters. 



The muscle fibers are rounded or conical, the end towards the tendon 

 being more obtuse than the other. Connection with the tendon is provided 

 by the perimysium, which is continuous with the tendon [Fig. 22]. The 

 connection of a muscle with a tendon, or with other tissues, at its rela- 

 tively moveable end, is called its insertion; the attachment at the relatively 

 fixed end of the muscle is its origin. In the cases of muscles inserted in 



