CAUSES AND PHENOMENA OF MOTION. 



19 



According to Schafer, the granules, which have been mentioned on 

 either side of Krause's membrane, are little knobs attached to the ends of 

 "muscle-rods;" and these muscle-rods, knobbed at each end and imbedded 

 in a homogeneous protoplasmic ground-substance, form the substance of 

 the muscles. This view, however, of the structure of muscle requires 

 further confirmation before it can be accepted. 



Although each muscular fibre may be considered to be formed of a 

 number of longitudinal fibrils, arranged side by side, it is ako true that 

 they are not naturally separate from each other, there being lateral 

 cohesion, if nofc fusion, 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 



FIG. 272. 



FIG. 273. 



FIG. 272. Muscular fibres from the heart, magnified, showing their qross-striae, divisions, and 

 junctions. (Kolliker.) 



FIG. 273. Network of muscular fibres (striated) from the heart of a pig. The nuclei of the mus- 

 cle-corpuscles are well shown, x 450. (Klein and Noble Smith.) 



split, not only into separate fibrils, but also occasionally into plates or 

 discs, each of which is composed of sarcous elements laterally adherent 

 one to another. 



Muscular Fibres of the Heart (Figs. 272 and 273) form the chief, 

 though not the only exception to the rule, that involuntary muscles are 

 constructed of plain fibres; but although striated and so far resembling 

 those of the skeletal muscles, they present these distinctions: Each 

 muscular fibre is made up of elongated, nucleated, and branched cells, 

 the nuclei or muscle-corpuscles being centrally placed in the fibre. The 

 fibres are finer and less distinctly striated than those of the voluntary 

 muscles; and no sarcolemma can be usually discerned. 



Blood and Nerve Supply. The voluntary muscles are freely sup- 

 plied with blood-vessels; the capillaries form a network with oblong 



