NERVOUS TISSUE 163 



MOTOR ENDINGS. The motor nerve endings are the terminations of 

 efferent nerves, in contact with smooth, cardiac or striated muscle fibers. 

 The nerves to the smooth muscles are a part of the sympathetic system. 

 They are non-medullated fibers which branch repeatedly, forming plexuses. 

 From the plexuses very slender varicose fibers proceed to the muscle cells, 

 in contact with the surface of which they end in one or two terminal or 

 lateral nodular thickenings. Probably each muscle cell receives a nerve 

 termination. Except that the nerve endings in heart muscle are a little 

 larger, often provided with a small 

 cluster of terminal nodules, they are 

 like those of smooth muscle. 



Striated muscles are innervated 



by the neuraxons of the ventral roots, B 



which grow out from cell bodies re- L FlG IS8 ._ MOTOR PLATES 



Within the Central System. A > Surface view, from a guinea-pig; B, vertical 

 * section, from a hedgehog. (After B6hm and 



form n1pTH<;f>t; nf mprliillatfvl von Davidoff.) g., Granular substance of the 



lorm piexubt motor p]ate . m ^ striat?d muscle . n . t nerve 



fibers in the perimysium, from which j| r r ; * r - terminal ramifications f the ne 

 branching medullated fibers extend 



into the fasciculi (Fig. 157). Each muscle fiber receives one of these 

 branches, or sometimes two placed near together. They are usually 

 implanted near the middle of the muscle fiber. The connective tissue 

 sheath of the nerve blends with the perimysium, and the neurolemma 

 is said to be continuous with the sarcolemma. On the inner side of 

 the sarcolemma the myelin sheath ends abruptly, and the nerve fiber 

 ramifies in a granular mass considered to be modified sarcoplasm, which 

 may contain muscle nuclei. This entire structure appears as a distinct 

 elevated area, estimated to average from 40 to 60 n in diameter; it has 

 been named the motor plate. A surface view and a section of a motor 

 plate are shown in Fig. 158. 



VASCULAR TISSUE. 



Vascular tissue includes the blood vessels, the heart, and the lymphatic 

 vessels, together with the blood and the lymph. 



BLOOD VESSELS. 



GENERAL FEATURES. The existence of blood vessels was well known 

 to the ancient anatomists, and a distinction was sometimes made between 

 pulsating and non-pulsating vessels. They were all included by Aristotle 

 under the term <\ty (vein). He described the two great vessels at the 

 back of the thorax, one of which is the vena cava; the other, as he states, 

 "by some is termed the aorta, from the fact that even in dead bodies 



