The brain of Acipenser. 167 
rubicundus these two tracts are wholly separate, the secondary vagus 
tract lying considerably farther ventrally than in A. ruthenus. The 
fibres which GORONOWITSCH says leave the spinal V to enter the 
dorso-lateral tract (acusticum) are probably the bundles of neurites 
of cells in the acusticum which I have described as running with 
the spinal V (page 77). His arcuate fibres to the spinal V are prob- 
ably arcuate fibres from the acusticum which run for a short di- 
stance with the spinal V (cf. pages 77 and 191). 
VAN GEHUCHTEN (94) has described the spinal V tract in the 
trout embryo, but did not describe the nucleus as such. He found 
collaterals from the V fibres shortly after entering the medulla which 
I have missed in Acipenser, probably owing to the obstacle offered 
to impregnation by the medullated tracts in the adult brain. VAN 
GEHUCHTEN describes also fibres which he ascribes to the X, turning 
caudad “pour constituer la racine descendante de la neuvième et 
de la dixième paire des nerfs craniens”. The fibres give off col- 
laterals toward cells which the author thinks belong to the central 
nucleus of the IX and X nerves. The cells send their neurites to 
the white column of the opposite side. Here it seems to me that 
VAN GEHUCHTEN has been misled by partial or imperfect im- 
pregnation. In his figure (fig. 13) he represents the descending root 
of the IX—X as superficial in position. All other authors are agreed 
in recognizing the vagus lobe as the center for these nerves in 
fishes. The vagus lobe borders on the ventricle and the descending 
root of the IX—X, so far as it exists in fishes, runs within the lobe. 
Further, the cells which constitute the end-nucleus to not send their 
neurites to the opposite side, but to the same side, forming the 
secondary vagus tract described by MAYSER, GORONOWITSCH, and 
myself (page 87). It seems to me very probable that the fibres 
described by VAN GEHUCHTEN are the spinal V components of the 
IX aud X nerves. The bundle described as the descending root. of 
the IX—X corresponds in position to the spinal V as described by 
MAYSER, KINGSBURY, and myself in Teleosts and Ganoids. The 
cells of the nucleus, as figured by VAN GEHUCHTEN, lie too far 
ventrally for either the nucleus of the IX—X or the spinal V. I 
think it more probable that they are commissural cells. I have 
examined numerous GOLGI preparations of Coregonus and Catostomus 
embryos which show the spinal V fibres and their collaterals, the 
spinal V components of the IX and X, and the end-branching of 
both at the junction of the cord and medulla, and they fully confirm 
