382 C. JUDSON HERRICK 



do so. The general arrangement of these fascicles of root fibers 

 is shown in figure 3. 



From this it follows that the white substance (stratum album) 

 of the sensory region of the oblongata from the level of the spinal 

 V tract dorsalward contains a series of longitudinal fascicles of 

 root fibers, each of which is a functional unit and whose fibers are 

 distributed peripherally to a particular species of sense organs. 

 These fascicles of root fibers occupy the entire stratum album of 

 this part of the oblongata, save for the presence of two additional 

 bundles of correlation fibers (the tracts a and h of Kingsbury) 

 and for a variable amount of a superficial nem'opil in the marginal 

 zone of the white substance. This arrangement is preserved 

 throughout the length of the acustico-lateral area of the oblon- 

 gata, whose limits are indicated in figure 3 by the distribution 

 area of the VIII and lateralis root fibers. 



The neurones of the gray layer (stratum griseum) of the sensory 

 region of the oblongata send their dendrites outward to arborize 

 among the terminals of these root fibers and the synaptic connec- 

 tions here effected are made in accordance with a definite func- 

 tional pattern; but this pattern is far less simple than that of the 

 root fibers and there are few groups of neurones of the gray sub- 

 stance which can be regarded as the specific or pure terminal nuclei 

 of particular functional systems of sensory roots. Most of these 

 neurones effect synaptic connection within the white layer with 

 more than one physiological type of root fibers, from which it 

 follows that the functions of primary receptor centers and corre- 

 lation centers are in these cases united to some extent within the 

 individual neurones of the second order. The white substance of 

 the medulla oblongata of these urodeles contains, in addition to 

 the motor and sensory root fibers, a large number of correlation 

 fibers, and the longer systems of these fibers are arranged in 

 definite correlation tracts. 



From the relations described in the preceding paragraph it is 

 evident that these correlation tracts are intermediate in physio- 

 logical type between those of the spinal cord of these larvae and 

 those of the oblongata of mammals. In the spinal cord of larval 

 urodeles there is little evidence of localization of function in the 



