174 Journal of Comparative Neurology. 



In a later paper, no mention is made of such relations of 

 the solitary bundle, and he is inclined to associate the pars mter- 

 inedia with the vago-glossopharyngeal end nidus. Further, re- 

 garding its central relations, the fasciatlus solitariiis is said in 

 birds to decussate just caudad of the metatela, — a relation not 

 as yet observed in man. The foregoing considerations seem to 

 warrant postponing the acceptance of the homology until a fuller 

 comparative study of this tract is made. Possibly t]\Q fascicuhis 

 conimmiis may embody both sensory termini for vagal fibers. 



Dorsal tracts. — As has already been stated, at the transition 

 from myel to oblongata the number of myelinic fibers in the dorsal 

 regions has greatly diminished, those remaining being almost 

 entirely such as constitute the ascending V and X. After the 

 beginning of the metatela, and up to the level of the first spinal 

 nerve, these tracts occupy the extreme dorsal position in the 

 spreading walls of the oblongata, the fibers for the tenth the 

 more dorsal. Cephalad of this point the ascending V and X 

 begin to migrate ventrad, leaving an amyelinic area to oc- 

 cupy the more dorsal portion. This area is also extended by 

 the closer apposition of the walls of the oblongata in the region 

 of the tenth nerve. Cephalad of X^ the ascending V is situated 

 in the ventro-lateral angle of the oblongata ; dorsad of it begin 

 to be distinguished the large fibers of the eighth nerve. In this 

 region myelinic fibers appear in the dorsal tracts, chiefly in the 

 extreme dorsal portion and the region just dorsad of the fibers 

 of the eighth, constituting the beginnings of the tracts named 

 for distinction tracts a and b. Between these two tracts the 

 region is almost entirely amyelinic with however scattered 

 bundles of myelinic fibers. Into this intermediate area enter 

 IX^ and IX^ and a portion of the "dorsal seventh" (Vllb*). 



Tract a, beginning in the region of the tenth nerve, 

 reaches its fullest development between the seventh and ninth 

 nerves. In the region of the seventh this tract loses its ex- 

 treme dorsal position, which is here occupied by an area of 

 amyelinic substance, apparently composed largely of ' ground 

 substance,' into which the dorsal portion of the "dorsal seventh 

 enters " (Vllb^). This is restricted to the immediate neigh- 



