414 yoiirnal of Cojnparative Neurology and Psychology. 



designate it the median funicular nucleus. Dorso-laterally of the 

 funicular nucleus and farther cephalad, forming a sort of cap upon 

 it, is the nucleus of the spinal V tract. This nucleus is more 

 closely related to the dorsal cornu of the spinal cord than is the 

 funicular nucleus. 



The funiculus dorsalis ends in both nuclei, as also does the 

 spinal V tract (Figs. 3, 4, 7 and 13). The funicular nucleus, how- 

 ever, receives far larger numbers of fibers from the fasciculus dorso- 

 lateralis than from both the other tracts mentioned. The nucleus 

 of the spinal V tract is distinguished from the funicular nucleus, 

 as in the mammals, by its clearer texture in Weigert preparations 

 and greater freedom from medullated fibers. The spinal V tract 

 and funicular nuclei and their associated fiber tracts form a pro- 

 tuberance caudad of the vagal lobes which is very conspicuous in 

 all siluroid brains. The two nuclei attain about equal proportions 

 in this protuberance (Fig. 3). 



The spinal V nucleus extends cephalad as far as the caudal end 

 of the vagal lobe. Here it shrinks to very small proportions and 

 is continued cephalad directly into the substantia gelatinosa 

 Rolandi (Fig. 5), the spinal V tract assuming a crescentic form in 

 cross-section with the substantia gelatinosa on the mesial side em- 

 braced within the horns of the crescent. From this substantia 

 gelatinosa voluminous secondary tracts pass through the ventral 

 commissure to the tractus bulbo-tectalis (Fig. 6) of the opposite 

 side (internal arcuate fibers). Other connections are made with 

 the formatio reticularis and the motor nuclei of the same side 

 and with the interior of the facial lobe. 



Figs. 9 to 12 illustrate various forms of neurones in the spinal V 

 nucleus. Fig. 13 shows the mode of ending of the fibers of the 

 spinal V tract in the nucleus, some of them passing through to 

 terminate in the median funicular nucleus. Figs. 11 and 13 show 

 that some fibers of the dorso-lateral fasciculus also end in this 

 nucleus. The small intrinsic neurones of Figs. 11 and 12 have short 

 branched neurites which end within the nucleus or in the adjacent 

 formatio reticularis of the same and the opposite side. The large 

 spinal V neurones of Figs. 9 and 10 do not show the full course of 

 the neurites. They probably reach the tractus bulbo-tectalis or 

 one of the other long secondary tracts. Weigert sections show 

 heavily medullated internal arcuate fibers from the spinal V nucleus 

 and substantia gelatinosa for their entire extent passing into the 

 tractus bulbo-tectalis. 



