ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 437 



tissue coverings blood-vessels and lymphatics find their way 

 as through other tissues. Along the course of the nerve 



Fig. 141. SECTION OF A NERVE TRUNK (HUMAN). (After Schafer.) 

 ep, epiueurium; per, perineurium; end, endoneurium ; v, blood-vessels; f, fat cells 

 stained with osniic acid. 



trunk funiculus after funiculus is given off as a separate 

 branch, and finally the individual funiculus is separated 

 until at the end of the nerve trunk this separation is ex- 

 tended to the nerve fibers themselves. 



The Development of Nerves. 



One of the most interesting chapters in embryology is 

 the development of the nervous tissues and the organs de- 

 rived from them. Such study shows that the nervous cells 

 are derived from peculiar cells called neuroblasts, which 

 cells by their amoeboid movements are able to place them- 

 selves in definite positions through the body and then later, 

 by a kind of polarization, are able to determine the direc- 

 tion of the nerves issuing from them. When one is re- 



