41 8 'Journal of Comparative Neurology and Psychology. 



In young Lepidosteus about 9 cm. long the relations of the com- 

 missura infima region are about as in the adult Amia as far as can 

 be determined by the study of haematoxylin preparations. In the 

 adult the disposition of the parts has been considerably altered. 

 The adult vagal lobe does not reach back to the lower end of the 

 fourth ventricle; but from its caudal end a diffuse tract of fibers, 

 both medullated and unmedullated, extends caudad mesially of 

 the funicular nucleus and adjacent to the wall of the fourth ven- 

 tricle, to the commissura infima. Here this tract rises up in the 

 taenia ventriculi quarti and decussates above the caudal end of the 

 fourth ventricle to end in the visceral commissural nucleus farther 

 caudad and ventrad. These visceral fibers are the only elements 

 in the commissura infima of this region so far as our preparations 

 demonstrate. The visceral commissural nucleus does not lie in 

 the median plane in association with its commissure, but some sec- 

 tions farther caudad and ventrad as a paired structure lying ven- 

 tromesially of the funicular nucleus of each side near the dorsal 

 fissure. The efferent tract from this nucleus, consisting of both 

 medullated and unmedullated fibers, passes out ventro-laterally 

 into the adjacent formatio reticularis. 



The funicular nucleus lies for the most part cephalad of the 

 calamus region instead of caudad of it, as in Amia. Some fibers 

 from the funicular nucleus or somatic sensory field may cross along 

 with the visceral fibers in the commissura infima, though I have 

 not been able to demonstrate them. The size of the somatic 

 commissura infima is reduced; possibly the strongly developed 

 efferent tracts from the funicular nuclei forming internal arcuate 

 fibers below the ventricle may compensate for the reduction of the 

 dorsal commissure. 



The combined nucleus of the spinal V tract and funicular nucleus 

 extends, as mentioned above, far cephalad of the commissura 

 infima into a somatic sensory field laterally of the caudal end of 

 the vagal lobe. It is quite sharply separate from the tuberculum 

 acusticum, which occupies the somatic sensory field cephalad of 

 it. The efferent fibers from the funicular nucleus can be easily 

 followed. They leave the nucleus in compact strands of heavily 

 medullated fibers which pass downward into the formatio reticu- 

 laris, ventral cornu, and in still larger numbers cross the ventral 

 raphe as internal arcuate fibers entering the fasciculus longitud- 

 inalis medialis. The funiculus dorsalis is unusually large in 



