Life and Health 



quite independently of the will, and even during sleep. We 

 frequently call the instruments of this activity involuntary 

 muscles. 



The former group, or skeletal muscles, from peculiarities 

 revealed by the microscope, are more accurately known as 

 striped or striated muscles. The latter group, or visceral 

 muscles, from the smooth appearance 

 which their cells present under the micro- 

 scope, are called unstriated muscles. 



Let us then remember the two kinds 

 of muscles as the striated (often called 

 voluntary) muscles, and the smooth, unstri- 

 ated (often called involuntary) muscles. 



74. Structure of the Striated Muscle. 

 The main substance which clothes the 

 bony framework of the body, and which 

 forms about two-fifths of its weight, is 

 the striated muscular tissue. These 

 skeletal muscles do not cover and sur- 



A, fiber separating into 



disks; B, fibriiis (highly round the bones in continuous sheets, 

 magnified); Across- b ut consist of separate bundles of flesh, 



section of a disk. ... 



varying in size and length. 



Each muscle has its own set of blood vessels and nerves, 

 and is enveloped in its own sheath of connective tissue, 

 known as the perimysium. When this external wrapping is 

 strong enough to be dissected off, it is known as fascia. 



Muscles are not usually connected directly with bones, but 

 by means of white, glistening cords or bands, called tendons. 



75. Microscopic Structure of Striated Muscle. If a small 

 piece of striated muscle be examined under a microscope 

 it is found to be made up of bundles of fibers. Each fiber 

 is enclosed within a delicate, transparent sheath, known as 

 the sarcolemma. If one of these fibers be further examined 



FIG. 29. Striated 

 Muscular Fibers. 



