OH. VI.] VOLUNTARY MUSCLE 70 



classification into voluntary and involuntary is shown in the follow- 

 ing table : 



1. Transversely striated muscular fibres : 



a. In skeletal muscle . . . VOLUNTARY. 



h. In cardiac muscle \ 



2. Plain muscular fibres : T 



In blood-vessels, intestine, uterus, I 

 bladder, etc. 



All kinds of muscular tissue are therefore composed of fibres, but 

 the fibres are essentially different from those we have hitherto studied 

 in the connective tissues. There, it will be remembered, the fibres 

 are developed between the cells; here, in muscle, the fibres are 

 developed from the cells; that is, the cells themselves become 

 elongated to form the muscular fibres. 



Voluntary Muscle. 



The voluntary muscles are those which are sometimes called 

 skeletal, constituting the whole of the muscular apparatus attached to 

 the bones.* 



Each muscle is enclosed in a sheath of areolar tissue, called the 

 Epimysium ; this sends in partitions, or septa, dividing off the fibres 



FIG. 102. A branched muscular fibre from the frog's tongue. (Kolliker.) 



into fasciculi, or bundles ; the sheath of each bundle may be called 

 the Perimysium. Between the individual fibres is a small amount of 

 loose areolar tissue, called the Endomysium. The blood-vessels and 

 nerves for the muscle are distributed in this areolar tissue. 



The fibres vary in thickness and length a good deal, but they 

 average lr jy inch in diameter, and about 1 inch in length. Each 

 fibre is cylindrical in shape, with rounded ends ; many become pro- 

 longed into tendon bundles (fig. Ill), by which the muscle is attached 

 to bone. As a rule they are unbranched, but the muscle fibres of the 

 face and tongue divide into numerous branches before being inserted 



* The muscular fibres of the pharynx, part of the oesophagus, and of the 

 muscles of the internal ear, though not under the control of the will, have the 

 same structure as the voluntary muscular fibres. 



