CENTRAL RELATIONS OF COMPONENTS. - 59 



clear. The fasciculus communis in the restricted {i. t'., 

 the original) sense in its typical form as we find it, for 

 example, in the Amphibia, conforms very closely to the 

 fasciculus solitarius of mammals and birds, as has been 

 pointed out by Strong. The same homology will hold in 

 the fishes, with this difference, that all of the communis 

 fibres of the vagus, and in some fishes of the glossopharyn- 

 geus as well, enter their terminal nucleus directly, without 

 participating in the formation of the longitudinal tract 

 known as the fasciculus communis. The relations of the 

 terminal nuclei are rather more complicated. In the 

 Amphibia, the spinal nucleus is the more important, the 

 chief IX+X nucleus being relatively small. In the bony 

 fishes the spinal nucleus has been either greatly reduced, 

 or, more probably, fused with the chief nucleus (lobus 

 vagi), which suffers more than a corresponding enlarge- 

 ment. In the mammals both nuclei are present and well 

 developed. We know from Kolliker's work ('96, p. 246) 

 that the fibres of the fasciculus solitarius of mammals 

 give off collaterals into the substantia gelatinosa surround- 

 ing this tract and there probably come into relation with 

 the cells of that region, which thus constitute a "spinal 

 sensory nucleus of X," (Van Gehuchten, '97, p. 483)- 

 The sensory IX+X nucleus of mammals is represented in 

 the lobus vagi of fishes, though it does not follow, of 

 course, that the two structures are exactly equivalent. 



This way of looking upon the sensory IX+X nucleus as 

 merely a specialized portion of the spinal nucleus of the 

 vagus or nucleus of the fasciculus solitarius receives the 

 strongest support from the recent work of Cajal ('96, p. 44) 

 by the Golgi method. In discussing the sensory terminal 

 apparatus of the IX+X nerves of the new-born mouse, he 

 writes: "There are, therefore, in this animal, not two 



