CENTRAL RELATIONS OF COMPONENTS. 45 



Most of these fibres turn caudad immediately upon enter- 

 ing the brain and constitute the spinal V tract. A large 

 bundle accompanies the motor root nearly to the median 

 line and constitutes the "deep portion of the descending 

 Vth" of Johnston ('98). Most of these fibres, both sen- 

 sory and motor, pass at once to the opposite side through 

 the commissura accessoria, but some of the motor fibres 

 terminate in, or more strictly, arise from, the motor V 

 nucleus and the fasciculus longitudinalis dorsalis of the 

 same side. The sensory fibres of this bundle probably 

 also, in part, cross to the opposite side, though they could 

 not be separately followed. Some of them appear to end 

 in a compact nucleus of very small cells lying very near to 

 the motor V nucleus and a little farther caudad. This I 

 take to be the " chief sensory nucleus" of the trigeminus. 

 It should be stated, however, that my knowledge of this 

 nucleus and its connections is not as precise as that of the 

 other roots described. No considerable number of tri- 

 geminal fibres turn cephalad from the origin of the 

 nerve. The nucleus lying under the cerebellum to which 

 Johnston traced sensory trigeminal fibres in Acipenser 

 was found, but no fibres were traced to it, nor were the 

 descending cerebellar fibres described by him and by 

 Goronowitsch discovered. No Golgi preparations were 

 made and I cannot deny the presence of such fibres in 

 relatively small numbers, as this region has not been ex- 

 haustively studied. 



The spinal V tract runs back very close to the lateral 

 wall of the oblongata and ventrally of all of the sensory 

 VII and of the VIII roots, but dorsally of the motor VII 

 (Fig. 19) and motor IX (Fig. 18) roots. The sensory IX 

 fibres emerge dorsally of it, the X fibres both dorsally and 

 ventrally. As the lobus vagi increases in size it crowds 



