174 OF PLEXUSES AND TERMINAL NETWORKS. 



at least two fibres ; and that in all cases there exist 

 complete circuits into the formation of which central 

 nerve cells, peripheral nerve cells, and nerve-fibres enter. 

 All these elements are in structural connection with 

 each other. [ u How to Work with the Microscope," 

 4th Ed.] 



232. Of plexuses and terminal networks. Every 

 one agrees that the larger nerve trunks are in many 

 instances so arranged as to form plexuses or net- 

 works, to which various names have been assigned 

 by anatomists, according to their position, general 

 form, origin, &c. ; but it was supposed that in many 

 cases nerves pursued an almost direct course to their 

 ultimate distribution, where they terminated in free 

 extremities, in cells, or by becoming continuous with 

 the texture they influenced. More careful observa- 

 tion has, however, demonstrated that all nerves 

 before they reach their finest ramifications form 

 microscopic networks or plexuses, arranged upon the 

 same plan as the coarser networks above alluded to ; 

 and I have been able to demonstrate that the fine 

 ramifications themselves constitute a plexus or net- 

 work, in which the component ultimate fibres are ar- 

 ranged in much the same manner as the large dark- 

 bordered fibres entering into the formation of one of the 

 ordinary plexuses. 



Careful observations upon the arrangement of par- 

 ticular nerve plexuses in the same texture at di fife- 

 rent periods of development have convinced me that 

 the ultimate terminal plexus of the embryo becomes 

 the plexus composed of coarser fibres of the infant 

 and child, and the plexus made up of bundles of 

 compound fibres of the adult. New ultimate nerve 

 plexuses gradually come into existence as the con- 

 stituent fibres of those previously formed grow and 

 slowly become converted into thick nerve-fibres. 

 That a continuous development of new nerve- fibres 

 takes place in the adult has been proved beyond ques- 



