TISSUES. 93 



the blood-vessels and terminate beneath the sarco- 

 lemma in special end plates called muscle plates. 

 These will be described under special nerve endings. 

 Non-medullated or sympathetic nerve fibers also 

 accompany blood-vessels, but they innervate the in- 

 voluntary musculature of arteries and veins. 



Distribution. Voluntary muscles are the skeletal 

 muscles, and make up the bulk of the body. 

 Striated fibers are present in the upper part of 

 the esophagus, and also constitute the platysma 

 muscle of the skin. 



Union with Tendon and Bone. The muscle 

 fibers terminate abruptly with tendon fibers. This 

 is not a direct end-to-end union, but the tendon 

 fibers fuse with the sarcolemma at an angle. In the 

 same way the muscle fibers unite with the periosteum 

 of the bone. At this point Sharpey's fibers are 

 particularly abundant and firmly anchor the peri- 

 osteum to the compact bone lamellae. 



General Considerations. A muscle tumor is called 

 a myoma. Tumors of plain muscle are common in 

 the wall of the uterus. They are benign, of slow 

 growth, and usually harmless. A tumor of striated 

 muscle fibers is very rare. The tissue is highly 

 specialized and the fibers therefore do not multiply 

 readily. If a muscle is injured or cut the voluntary 

 fibers regenerate partly from the cut end and partly 

 from free muscle nuclei that are shed into the wound, 

 but mostly by connective-tissue repair that leaves a 

 permanent scar. 



The physiological action of plain muscle is slow, 

 producing peristaltic contractions. That of volun- 

 tary muscle is rapid, as in the wings of insects. 



