THE MUSCLES. 529 



In the coats of the blood-vessels and in the hollow viscera is 

 another variety of muscular fibers, often making a distinct layer or 

 layers to these organs. In this kind the fibers do not have the cross- 

 striped appearance, but are plain, or unstriped. Nearly all of these 

 are not under the control of the will, and are, hence, involuntary. It 

 must here be noted, however, that the muscle of the heart which, 

 as everyone knows, is an involuntary muscle is exceptional to this 

 class of muscle in that its fibers are very plainly cross-striped. Never- 

 theless, it presents differences from the striped fibers of skeletal 

 muscles; so that it has become customary with very many authors 

 to class it under the separate title cardiac muscular tissue. 



The muscular fibers of the skeleton are generally collected into 

 distinct organs of various sizes and shapes which have at each end 

 a tendon by which they are attached to the skeleton. 



The fibers of the muscles are collected together into bundles, 

 called fasciculi. In the fasciculi the fibers are parallel, so that the 

 fasciculi wind from one tendinous end to the other, except in a few 

 muscles like the rectus abdominis. In this instance the body of 

 the muscle is interrupted by interposed tendinous tissue. The fas- 

 ciculi themselves do not mingle with one another and, for the most 

 part, run parallel, although in many cases they converge to their 

 tendinous endings. 



The covering of the entire muscle is termed the epimysium, and 

 a connective-tissue envelope. The covering of areolar tissue which 

 insheathes the fasciculi of the muscle is spoken of as the perimysium. 

 The latter, a septum from the epimysium, furnishes to each fascicu- 

 lus a special covering as well as furnishing it with blood-vessels and 

 nerves. Within each compartment lie a number of muscle-fibers 

 which are usually parallel to one another and held together by a very 

 delicate reticular connective tissue. This areolar network is called 

 the endomysium, but does not make a continuous covering and so 

 cannot be said to form sheaths for them. Each fiber of the muscle, 

 however, has a tubular sheath, but this sheath is not composed of the 

 areolar tissue just mentioned. The special function of the areolar 

 tissue seems to be to connect the fasciculi and fibers, and to support 

 id conduct the blood-vessels and nerves in their ramifications be- 

 tween the various parts. 



FASCICULI in form are prismatic, so that a transverse section 

 shows an angular outline. The thickness of a fasciculus, as well as 

 the number of fibers of which it is composed, varies. The texture of 

 a muscle, whether coarse or fine, depends upon the large or small 



