180 PRINCIPLES OF PHYSIOLOGY 



as a neurone, the fine processes produced by 

 some of the poles constitute branchlets or 

 dendrites ; a mass of dendrites forms a dendron, 

 or tree-like structure, and the process that is 

 the origin of a nerve-fibre is the axon, or 

 central rod. Next, imagine the branches 

 of two adjacent trees freely intermingling, but 

 not touching each other. This is a picture 

 of the relation of two or more neurones. 

 The dendrites do not form a network, as was 

 once supposed ; they do not even touch ; 

 there is, as has been aptly said, contiguity 

 but not continuity of structure Where den- 

 drites come close together without touching, 

 as if they were almost clasping, we have 

 what is called a synapsis. The dendrites 

 may sometimes form a network in close 

 proximity to, or even enveloping, the body of, 

 an adjacent neurone. This network is called 

 an arborization. We do not know what 

 phenomena occur at a synapse or arbori- 

 zation. The axon is a process of a neurone, 

 and it may be of great length or it 

 may be short. Thus axons from neurones 

 in the lower part of the spinal cord, for 



