346 C. JUDSON HERRICK 



the white layer throughout the brahi. In the medulla oblongata 

 these appear darker in preparations stained by the method of 

 Cajal than do the nuclei of the gray layer. In figures 4 to 18 the 

 latter are drawn as light circles, while the nuclei of the white layer 

 are drawn in solid black. The character of the cells to which 

 these nuclei belong is unknown. 



Within the stratum album, moreover, root fibers and other 

 tracts are arranged in a definite pattern and the dendrites of the 

 neurones of the stratum griseum extend outward among these 

 tracts and the associated areas of neuropil, thus effecting their 

 respective synaptic connections. The axones of these neurones 

 also enter the stratum album and in this way the correlation 

 tracts are formed. Not until the connections of the axones and 

 dendrites of the individual neurones are fully known is it possible 

 to understand their physiological significance; and since the 

 mastery of these histological details is exceedingly difficult, our 

 knowledge of the internal structure of the amphibian brain is still 

 father fragmentary. The application of appropriate neurological 

 tnethods, however, reveals a very definite functional localization, 

 within the stratum album, with a corresponding specificity in the 

 related neurones of the stratum griseum. The analysis of these 

 relations in the oblongata of Amblystoma is the purpose of this 

 research. 



THE SPINAL CORD 



The spinal cord of urodeles has been described by several 

 authors, most fully by Van Gehuchten ('97), most of whose obser- 

 vations on larval Salamandra I have confirmed in my own Golgi 

 preparations of the upper segments of the spinal cord of larval 

 Amblystoma. The literature of this subject has been fully re- 

 viewed by Van Gehuchten in the paper cited and need not be 

 further considered here. 



In the half grown larvae from which the present description is 

 chiefly drawn the configuration of the gray and white substance 

 of the spinal cord is quite different from that of the adult. The 

 stratum griseum, containing the cell bodies of practically all of the 

 neurones of the cord, is very wide and it extends quite to the dorsal 



