MUSCULAR FIBRES OF THE HEART. 587 



elements, which are separated from each other by a bright 

 space formed of a pellucid substance continuous with 

 them. A fine streak can be sometimes discerned passing 

 across the bright interval between the sarcous elements. 

 Dr. Sharpey believes that, even in a fibril so constituted, 

 the ultimate anatomical element of the fibre has not been 

 isolated. He believes that each fibril with quadrangular 

 sarcous elements is composed of a number of other fibrils 

 still finer, so that the sarcous element of an ultimate fibril 

 would be not quadrangular but as a streak, and the dark 

 transverse streak on the bright space but a row of dots. In 

 either case the appearance of striation in the whole fibre 

 would be produced by the arrangement, side by side, of the 

 dark and light portions respectively of the fibrils (fig. 154). 



Although each muscular fibre may be considered to be 

 formed of a number of longitudinal fibrils, arranged side 

 by side, it is also true that they are not naturally separate 

 from each other, there being lateral cohesion of each 

 sarcous element with those around and in contact with it ; 

 so that it happens that there is a tendency for a fibre to 

 split, not only into separate fibrils, but also 

 occasionally into plates or disks, each of 

 which is composed of sarcous elements 

 laterally adherent one to another. 



The muscular fibres of the heart, although 

 striped and resembling closely those of the 

 voluntary muscles in their general structure, 

 present these distinctions : They are finer 

 and more faintly striated, they branch and 

 anastomose one with another, and no sar- 

 colemma can be usually discerned (fig. 155). 



The voluntary muscles are freely supplied with blood- 

 vessels ; the capillaries form a network with oblong meshes 



* Fig. 155. Muscular fibres from the heart, magnified, showing their 

 cross-strise, divisions and junctions (from Kolliker). 



