MUSCULAR TISSUES 



21 



enter the muscle along connective tis- 

 sue 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-tis- 

 sue septa around the fibers. There 

 are also definite lymph-vessels which 

 accompany the blood-vessels within 

 the muscle. This tissue is also sup- 

 plied with both motor and sensory 

 nerves, by means of which the stimuli 

 are carried to and from the muscle 

 fibers. 



(2) Heart muscle occupies an in- 

 termediate position between the stri- 

 ated voluntary muscle and the non- 

 striated involuntary muscle tissue. It 

 is characteristic in that it is striated 

 and involuntary. The following is a 

 brief summary of its chief distin- 

 guishing features: (i) Its fibers are 

 united with each other at frequent in- 

 tervals by short branches, (2) its 

 fibers are smaller and their striation is 

 less marked than in voluntary mus- 

 cle, (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 distribution may be out- 

 lined as follows: (i) It is found in 

 the digestive tract from the middle of 



FIG. 18. Cells of 

 smooth muscle tissue 

 from the intestinal 

 tract of rabbit. (From 

 Yeo after Ranvier.} 



A and B, muscle-cells in 

 which differentiation of the 

 protoplasm can be well seen. 



