MUSCULAR TISSUES 



21 



Striated muscular tissue is very richly 

 supplied with blood-vessels. The larger 

 arteries and their accompanying veins 

 enter the muscle along connective tissue 

 septa and then break up into smaller^ 

 branches and, finally, into a capillary 

 network which supplies the individual 

 muscle fibers. They are also supplied 

 with lymphatics which occupy the clefts 

 in the connective-tissue septa around the 

 fibers. There are also definite lymph- 

 vessels which accompany the blood- 

 vessels within the muscle. This tissue 

 is also supplied with both motor and 

 sensory nerves, by means of which the 

 stimuli are carried to and from the mus- 

 cle fibers. 



(2) Heart muscle occupies an inter- 

 mediate position between the striated 

 voluntary muscle and the non-striated 

 involuntary muscle tissue. It is charac- 

 teristic in that it is striated and invol- 

 untary. The following is a brief sum- 

 mary of its chief distinguishing features: 



(1) Its fibers are united with each other 

 at frequent intervals by short branches, 



(2) its fibers are smaller and their stria- 

 tion is less marked than in voluntary 

 muscle, (3) it has no sarcolemma, and 

 (4) its nuclei are situated within the 

 substance of the fiber and not upon it. 



(3) Smooth or involuntary muscle 

 occurs in bundles and thin sheets chiefly 

 in viscera and blood-vessels. Its general 



FIG. 18. Cells of smooth 

 muscle-tissue from the 

 intestinal tract of rabbit. 

 (P'rom Yeo after Ranvier.} 



A and B, muscle-cells in 

 which differentiation of the 

 protoplasm can be well seen. 



