9 2 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



breast of a bird, the fibers have a poor supply of 

 sarcoplasm and a predominance of sarcostyles. In 

 red meat the fibers are rich in sarcoplasm and have a 

 less supply of the sarcostyle protoplasm. In the 

 myology of man both kinds of fibers are present. 

 The white fibers are more powerful but have less 

 endurance; that is, if held in tetanic contraction 

 with no interval of rest they would tire quicker than 

 the red fibers. The pectoral muscle of birds is 

 powerful, but would soon tire but for the interval 

 of rest that intervenes between the strokes of the 

 wing; that is, during its upward movement. 



Fig. 59. Three voluntary muscle fibers from an injected muscle, show- 

 ing network of blood-capillaries. 



Blood Supply. Blood-vessels follow the con- 

 nective tissue of a muscle, and' penetrate to the 

 individual fibers where they break up into capil- 

 laries. These vessels run, as a rule, parallel to the 

 fibers, forming a network with anastomosing 

 branches. They extend in a varicose manner 

 between the fibers in such a way that when a muscle 

 contracts they readily adjust themselves, without 

 breaking. 



Nerve Supply. Medullated nerve fibers accompany 



