OH. n.] VOLUNTARY MUSCLE. 85 



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 



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



fibres 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 ^ v inch in diameter, and about i inch in length. Each 

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

 longed into tendon bundles (fig. in), by which the muscle is at- 

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

 fibres of the face and tongue divide into numerous branches 

 before being inserted to the under surface of the skin, or mucous 

 membrane (fig. 102). The fibres in these situations are also finer 

 than in the majority of the voluntary muscles. 



Each fibre consists of a sheath, called the sarcoleninia, enclosing 



* 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. 



