STRIATED OR STRIPED MUSCLE. 221 



Characters of this beautiful texture very distinctly, 

 and specimens may be j^repared without difficulty. 



Striped or voluntary muscle may consist of wide 

 or narrow fibres arranged perfectly parallel to one 

 another, or the muscle may consist of two or more 

 layers, the constituent fibres of which cross one 

 another at right angles. In some cases the fibres are 

 very irregularly aiTanged, and cross in various direc- 

 tions. Striped muscular tissue also exists in the 

 form of conical fibres which gradually taper towards 

 one extremity into a tendon, Plate XIV, page 271 . The 

 fibre in some cases divides and subdivides almost like 

 the branches of a tree, in which case it is termed 

 branching muscle. This is found in the frog's tongue, 

 page 271. Lastly, striped muscular tissue may be 

 arranged so as to form a net-work, a beautiful ex- 

 ample of which exists in the auricle of the frog's heart. 



Structure of an elementary fibre or fasciciihis. — A 

 good general idea of the structure of an elementary 

 fibre of striped muscle will be formed if a specimen 

 from the large water-beetle, Dyti.scus marginalis, be 

 carefully examined. Here the transverse markings 

 are seen upon a considerable scale, and the elementary 

 fibre is very large, Fig. -3, plate VI, see also Fig. 1 . The 

 contractile tissue has ruptured within the sarcolemma, 

 and has cleaved transversely in sevei-al places. Two 

 of Bowman's discs are detached from the rest of the 

 contractile tissue, and lie free in the tube of the sar- 

 colemma. The masses of bioplasm concerned in 

 their formation are seen in the centre of the disc, a. 

 The contractile tissue, with the delicate closed tube of 

 sarcolemma forming its outer limit, constitutes an 

 elementary fibre or fasciculus of striped or voluntary 

 muscle. The contractile material which occupies the 

 tube of the sarcolemma may be split up in two direc- 

 tions — longitiidinally into filrillce, and transversely 

 into disls — as was first demonstrated by Bowman. 



In one specimen from the frog the contractile tissue 



