MUSCLES 



363 



moves least is the origin. Muscles are named biceps or triceps 

 (two-headed or three-headed, depending on the number of tendons 

 found at the origin) : the gastroc- 

 nemius, already referred to, is a 

 biceps muscle; the large muscle 

 forming the front part of the thigh 

 is a triceps muscle. 



Microscopic Structure of Vol- 

 untary Muscle. — With a sharp pair 

 of scissors cut through the belly of a 

 muscle at right angles to the long axis ; 

 examination will show that it is com- 

 posed of a number of bundles of fibers. 

 These fibers are held together by a 

 sheath of connective tissue called the 

 perimysium (Lat. = around the mus- 

 cle). Each of these bundles may be 

 separated into smaller ones. If we 

 continue this so as to separate into the 

 smallest possible bits that can be seen 

 with the naked eye, and then examine 

 such a tiny portion under the com- 

 pound microscope, it will present some- 

 what the appearance of the figure. 

 The muscle is seen to be made up of 

 a number of tiny threads which lie 

 side by side, held together by the peri- 

 mysium. Each thread consists of sev- 

 eral muscle fibers, each of which is 

 inclosed in a tiny sheath. A single 

 fiber under the compound microscope 

 appears to have alternate light and 

 dark bands running at right angles to 

 its long axis. This gives the bundle of 

 fibers a striped appearance. Nuclei are 

 seen here and there, showing that the 

 muscle is made up of cells. Such is 

 the structure of muscle fibers which are 

 under the control of the will, the vol- 

 untary muscles as they are called. If it 

 were possible to prepare muscle fibers in such a manner as to trace the path 

 of the nerves in these fibers, such nerves would be seen to end in little 



A bit of voluntary muscle fiber, showing 

 the cross striations as seen under the 

 microscope. 



Motor nerve endings in striated muscle 

 fibers as seen vmder the microscope. 



