NEURITES. 205 



The processes of nerve-cells are of two very distinct kinds, 

 dendrites or protoplasmic processes, and neurites or axis- 

 cylinder processes. 



The dendrites, or protoplasmic processes, are long slender ex- 

 tensions or processes from the body of the nerve-cells, usually 

 dividing and subdividing into branches like a tree, forming 

 extensive "arborizations" in the vicinity of the cell. As 

 they divide, the branches decrease in size to fine terminal 

 twigs, which have either pointed or rounded ends. The ter- 

 minals of dendrites have been called teledendrites. The num- 

 ber of dendrites given off by each nerve-cell varies ; there may 

 be none or several. The cerebro-spinal nerve-cells possess the 

 most numerous and best developed dendrites, each having a 

 number of such processes, while the cells of the ganglia are less 

 abundantly supplied with them, and unipolar cells lack them 

 altogether. The dendrites of neighboring nerve-cells inter- 

 lace and lie in close relation with one another ; but according 

 to the neuron theory they are not actually united or structu- 

 rally continuous together. 



The neurites, axis- cylinder processes, or neuraxons, are 

 slender filamentary processes from nerve-cells, which are pro- 

 longed as, and become continuous with, the axis-cylinders of 

 nerve-fibres, and as such are greatly prolonged, often extend- 

 ing to the periphery of the body. They acquire medullated 

 envelopes at a short distance from the cells, and thus become 

 converted into nerve-fibres. Sometimes, within the substance 

 of the nerve-centres, neurites give off delicate, short lateral 

 branches, the collateral fibres, but aside from these and except 

 at their distal ends neurites do not branch, and their diameter 

 is uniform throughout. All nerve-cells possess one neurite, 

 sometimes more than one ; if a cell has but one process, that 

 process is a neurite. 



At their distal ends neurites or nerve-fibres usually termi- 

 nate in fine branches; these distal terminations have been 

 called teleneurites. According to the length of the neurites 

 and the situation of the teleneurites, two types of nerve-cells 

 or neurons are recognized. 



Nerve-cells of the first type have long neurites extending 

 to the visceral, distal, or peripheral portions of the body, 

 where their terminals or teleneurites are situated. 



