4o8 Journal of Comparative Neurology and Psychology. 



of intrinsic neurones of the vagal lobe and has broad efferent paths, 

 to the formatio reticularis. 



A third correlation center belonging to the visceral sensory 

 column is the nucleus commissuralis. This nucleus, first de- 

 scribed in the mammals by Cajal ('96, p. 46), is very large in all 

 fishes having large gustatory centers. In Ameiurus it is a highly 

 developed structure forming ^ median protuberance above the cau- 

 dal tip of the fourth ventricle just behind the vagal lobes, and 

 directly continuous cephalad with the nucleus intermedius of the 

 vagal lobe, some neurites from the latter nucleus terminating here 

 (Herrick, '05, p. 432). The caudal ends of the vagal lobes fuse 

 in the median line in the region of the n. intermedius and this area 

 of fusion is produced backward into the commissural nucleus 

 (Figs. 7, 6 and 5), which with its commissure lies dorsally of the 

 nucleus ambiguus. 



The nucleus commissuralis receives, as we have seen, fibers from 

 the most caudal sensory root of the vagus. That these are not 

 motor fibers is shown by their mode of arborization in Golgi 

 preparations (Figs. 13 and 14). The motor vagus roots from 

 the nucleus ambiguus lie farther ventrally. The commissural 

 nucleus also receives secondary tracts from the vagal lobe (Fig. 

 7, desc. sec. X). The cephalic end of the commissural nucleus 

 receives slender fascicles of medullated fibers from the descending 

 secondary gustatory tract arising in the facial lobe of the same side. 

 These detach themselves from the inner border of their tract and 

 ascend along the mesial aspect of the substantia gelatinosa, thence 

 plunging directly mesad into the commissural nucleus (Fig. 6,1.). 



Large feebly medullated and unmedullated tracts pass from this 

 nucleus to the formatio reticularis (Fig. 5), and perhaps also smaller 

 tracts to the cephalic end of the funicular nucleus. Sagittal sec- 

 tions of Ameiurus by the Golgi method show that the tracts from 

 the commissural nucleus to the formatio reticularis constitute the 

 eff'erent path from this nucleus. These fibers, having reached 

 the region laterally of the cephalic end of the canalis centralis, give 

 off collaterals and often divide into ascending and descending 

 branches. The cells of the commissural nucleus are small and 

 arranged chiefly along the dorsal surface of the nucleus. The 

 richly branched dendrites ramify throughout the nucleus among 

 the termini of the vagus root fibers, the neurite arising from the 

 dendrite. The arrangement of these cells resembles somewhat 



