368 C. JUDSON HERRICK 



analysis of the peripheral nerve roots and their central courses the 

 impression made upon me by these preparations was that the 

 apparatus for the central analysis and correlation of sensory 

 stimuli from the cranial nerves was almost as simple and undif- 

 ferentiated as in the spinal cord ; but after more careful study it 

 became evident that the dendrites of the neurones of the gray 

 substance are distributed throughout the white substance in 

 accordance with a very definite functional pattern, some of the 

 details of which can now be stated. 



The dendrites of the neurones of the gray substance, as in the 

 spinal cord, may ramify widely throughout the white layer, and 

 in very few cases have I observed all of the dendritic arboriza- 

 tions of any neurone entering into functional connection with the 

 terminals of a single sensory root. In other words, the medulla 

 oblongata of larval Amblystoma contains no groups of neurones 

 which may be regarded as specific terminal nuclei for the various 

 sensory nerve roots described in the preceding section. On the 

 other hand, almost every one of the hundreds of neurones of the 

 sensory region of the oblongata which are satisfactorily impreg- 

 nated in my preparations sends its dendrites outward to effect 

 synaptic relation with the termini of two or more distinct sensory 

 roots. Moreover, these dendrites are not spread out at random 

 among the fascicles of root fibers and other tracts, but the arrange- 

 ment seems to conform to a definite functional pattern in each 

 case. I have by no means completed the analysis of these rela- 

 tions, but the observations already made give a fairly exact 

 general idea of the plan of organization of these brains. 



The neurones associated with the fasciculus solitarius (visceral 

 sensory system) appear to be more sharply circumscribed than 

 those related to any other functional system, and some of these 

 appear to be functionally related to no root fibers other than 

 those represented in this fasciculus (fig. 40, nuc.f.soL). Neverthe- 

 less nearly all of the neurones related to the fasciculus solitarius 

 send some of their dendrites also into the region of distribution of 

 the spinal V root or some other distinct system (see fig. 38) . 



The region dorsally of the fasciculus solitarius and spinal V 

 root receives the VIII and lateral line roots, and the gray substance 



