g6 Journal of Comparative Neurology. 



by way of the dorsal roots. In the rostral portion of the spinal 

 cord there appears a bundle of fibers, varying in size in differ- 

 ent vertebrates, which lies dorsal to Clarke's column and in- 

 creases in size as it passes forward. The fibers of this bundle 

 come from the roots of the X, IX, and VII nerves and appear 

 to end in the splanchnic center in the rostral part of the cord, 

 since the longitudinal tract disappears in all cases (except Petro- 

 myzon ?) caudal to the first few segments of the cord. Near 

 the junction with the medulla these bundles approach the dorsal 

 raphe and rise to the dorsal surface. Here a larger number of 

 fibers from the same sources decussate (commissura infima 

 Halleri) and end in a median nucleus first described by Cajal 

 (i) for mammals. This commissure and nucleus mark roughly 

 the limit between the cord and medulla. The splanchnic cen- 

 ter continues rostrad from the commissure, in lower forms con- 

 tinuous with the median nucleus, and becomes greatly enlarged 

 as the lobus vagi of fishes or the nuclei of the fasciculus com- 

 munis or solitarius of higher forms. Its position in the medulla 

 is the same as in the cord, ventro-median to the somatic sensory 

 center. It continues forward to the point of exit of the fasci- 

 ci'.lus communis VII root and there abruptly terminates. 



Although considerably larger in the brain than in the cord 

 of all vertebrates, the splanchnic center varies enormously in 

 size in the lower vertebrates. This variation is due in part to 

 differences in the extent of visceral area to be innervated, but 

 far more to the differences in the number" of end-buds, espe- 

 cially in the skin. In Petromyzon, where end-buds are few, 

 the splanchnic center in the medulla is very small in its rostral 

 part, is largest near the commissure, and is larger in the cord 

 than in other vertebrates. The center is simpler in structure 

 than in higher fishes. In selachians (lo) it is smaller than in 

 teleosts, in ganoids it is well developed, while in some teleosts 

 in which end-buds are exceedingly numerous, it forms the 

 largest and most conspicuous division of the medulla. It is 

 noteworthy that the splanchnic sensory center does not extend 

 as far rostrad as the splanchnic motor, and that both are far 

 out-reached by the somatic divisions. 



