THE MUSCULAR SYSTEM. 399 



The sarcous elements and Krause's membranes are doubly refracting, 

 the rest of the fibre singly refracting. (Briicke. ) 



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 im- 

 bedded in a homogeneous protoplasmic ground-substance, form the sub- 

 stance of the muscles. This view of the structure of muscle requires 

 further confirmation. 



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 cohe- 

 sion, if not fusion, of each sarcous element with those around and in con- 

 tact 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 



FIG. 280. From a preparation of the nerve-termination in the muscular fibres of a snake, a, 

 End plate seen only broad surfaced. 6, End plate seen as narrow surface. (Lingard and Klein.) 



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

 one to another. 



Muscular Fibres of the Heart (Figs. 92 and 93) 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 voluntary 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 supplied 

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

 around the fibres on the outside of the sarcolemma. No vessels pene- 

 trate the sarcolemma to enter the interior of the fibre. Nerves also are 

 supplied freely to muscles; the voluntary muscles receiving them from 



