PHYSIOLOGY OF NERVE TISSUE. 65 



each of which possesses a separate investment of connective tissue the peri- 

 neurium. Within this membrane the nerve-fibers are supported by a fine 

 stroma the endoneurium. After pursuing a longer or shorter course, the 

 nerve trunk gives off branches, which interlace very freely with neighboring 

 branches, forming plexuses, the fibers of which are distributed to associated 

 organs and regions of the body. From their origin to their termination, how- 

 ever, nerve-fibers retain their individuality, and never become blended with 

 adjoining fibers. 



FIG. 8. TRANSVERSE SECTION OP A NERVE (MEDIAN). 

 ep. Epineurium. pe. Permeurium. ed. Endoneurium. 



As nerves pass from their origin to their peripheral terminations, they give 

 off a number of branches, each of which becomes invested with a lamellated 

 sheath an offshoot from that investing the parent trunk. This division of 

 nerve bundles and sheath continues throughout all the branches down to the 

 ultimate nerve-fibers, each of which is surrounded by a sheath of its own, 

 consisting of a single layer of endothelial cells. This delicate transparent 

 membrane, the sheath of Henle, is separated from the nerve-fiber by a con- 

 siderable space, in which is contained lymph destined for the nutrition of the 

 fiber. Near their ultimate terminations the nerve-fibers themselves undergo 

 division, so that a single fiber may give origin to a number of branches, 

 each of which contains a portion of the parent axis-cylinder and myelin. 



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