THE PROBLEM OF NEURON PATTERN 159 
brief survey serves merely to call attention to some of 
the more common and characteristic aspects of neuron 
pattern. 
The most characteristic feature of the differentiation 
of the neuron from the neuroblast is the appearance of 
outgrowths of the cell body which often develop an 
extremely complex system of branches, resembling the 
branching of the multiaxial plants. In most vertebrate 
neurons the two kinds of outgrowths, axon and dendrites, 
are clearly distinguishable. The axon is slender and of 
uniform diameter over all or most of its length and 
possesses a characteristic structure differing from that 
of other parts of the cell. The axon may extend for a 
long distance from the cell body with no, or very few, 
branches, as in many motor cells (Fig. 45), or it may 
give rise to lateral branches, the collaterals, in the 
immediate vicinity of the cell body (Fig. 46). In other 
neurons it may break up into branches and terminate 
within a short distance from the cell (Fig. 47). It may 
terminate in a complex system of branches, the terminal 
arborization, near or far away from the cell body, or it 
may end with little or no branching. The relations of 
axons to dendrites of other neurons also differ widely in 
different cases. In some the axon or some of its branches 
form extensive spirals about the dendrite while in others 
the approach is more or less direct. Usually a neuron 
gives rise to only one axon, though dioxonic and even 
polyoxonic neurons occur, and usually also the axon is 
the primary outgrowth of the cell. But some neurons 
remain without axons. 
The dendrites, on the other hand, are structurally 
very similar to the cytoplasm of the cell body and are 
