STRUCTURE OF THE NERVOUS SYSTEM 



28 5 



side plan is seen in that disposition of the neurons which 

 enables them to form the nerves and the ganglia, as well 

 as the brain and spinal cord. The end-to-end connections 

 are necessary to the work which the neurons do. 



Side-by-side Connections. On separating the ganglia 

 and nerves into their finest divisions, it is found that the 

 nerves consist of axons, while the ganglia are made up 

 mainly of cell-bodies and dendrites. The axons lie side 



FIG. 1 28. Diagrams illustrating arrangement of neurons. A, B. Gan- 

 glia and short segments of nerves. I. Ganglion. 2. Nerve. In the ganglion 

 of A are end-to-end connections of different neurons; in the ganglion of B 

 are the cell-bodies of di-axonic neurons. C. Section of a nerve trunk. 

 I. Epineurium consisting chiefly of connective tissue. 2. Bundles of nerve 

 fibers. 3. Covering of fiber bundle, or perineurium. 4. Small artery and 

 vein. 



by side in the nerve, being surrounded by the same pro- 

 tective coverings, while the cell-bodies form a rounded 

 mass or cluster, which is the ganglion (Fig. 128). But the 

 axons, in order to connect with the cell-bodies, must termi- 

 nate within the ganglion, so that they too form a part of it. 

 To some extent, also, axons pass through ganglia with which 

 they make no connection. The neurons in the brain and 

 spinal cord also lie side by side, but their arrangement is 

 more complex than that in the nerves and ganglia. 



