THE PROBLEM OF NEURON PATTERN 165 



dendrites arise opposite the axon, but numerous other 

 dendrites are present on all parts of the cell surface and 

 extend in all directions. Evidently the situation at this 

 stage is very different from that in the mature neuron. 

 The primary dendrites are more or less definitely 

 oriented, but many others exist which show no uniform 

 orientation. These latter are evidently temporary and 

 are resorbed in later stages. Cajal distinguishes a 

 period of outgrowth and one of regulation and order- 

 ing of the dendrites. Here, as in the pyramidal cell, 

 very considerable changes occur in the course of devel- 

 opment, both in localization and orientation of the 

 dendrites. 



The developmental stages of the axon of the Purkinje 

 cell also show extensive changes. In the new-born 

 infant the axon shows numerous, much-branched 

 collaterals near the cell body as well as a number of 

 longer and less-branched collaterals. In later stages 

 extensive resorption of the shorter, highly branched 

 collaterals occurs, and in the adult only the longer, less- 

 branched outgrowths remain. This neuron evidentally 

 gives rise to many outgrowths which are only temporary 

 and play no part in the final morphological and functional 

 relations of the neuron. Apparently a selection among 

 the outgrowths takes place during development and 

 presumably on a functional basis, that is, those out- 

 growths which play an essential part in the functional 

 relations of later stages persist, while those which are 

 not thus functionally active disappear, like larval organs 

 and other temporary structures in the development of 

 organisms. It is evident, however, that the appearance 

 of these outgrowths must be determined by certain 



