1 36 STRONG. [Vol. X. 



curves cephalad. The fibres of this root are exclusively coarse, 

 very uniform in size, and apparently have an internal origin 

 similar to those of the dorsal VII, which they resemble in every 

 way. At 926 it separates from the medulla and proceeds ecto- 

 caudo-ventrad a short distance when it is joined on its ventral 

 side by the second root of the IX + X. 



The second root emerges from the medulla (936) at some in- 

 terval from the first and, as mentioned above, at a lower level 

 (PI. XI, Fig. 37). The bulk of its fibres are derived from the 

 fasciculus communis. It is joined, however, on its ventral side 

 by a slender bundle of fibres which, as they penetrate further 

 into the medulla, curve ventrad and have an origin considerably 

 further inward and ventral to that of the rest of the root. 

 They, apparently, are connected with a group of cells, but no 

 actual continuity with processes of cells was observed. These 

 fibres are coarser than those from the fasciculus communis. 

 This is, undoubtedly, a motor rootlet and seems to be com- 

 parable in position and general characteristics with the motor 

 roots of the Trigeminus and Facialis. It is not represented in 

 Fig- 37» which is drawn from a Golgi preparation in which the 

 fibres of this ventral rootlet were not impregnated. As will be 

 observed in the figure, the fibres of this second root break 

 through the ascending Trigeminus tract in order to reach the 

 exterior. 



The third root, preceded sometimes by a minute intermediate 

 rootlet, often emerges in close juxtaposition with the second 

 root. This root has, at least, a threefold origin. As shown in 

 Fig. 36, the dorsal position of this root is derived from the 

 ascending tract of the Trigeminus. This derivation is, un- 

 doubtedly, contrary to the views generally held as to the origin 

 of the IX + X, but is, I believe, shown to be correct not only 

 by a study of the origin of the roots themselves but also by the 

 nature of certain of the branches of the IX + X as described 

 hereafter. As seen in Fig. 36, these fibres come from the 

 lower part of the ascending Trigeminus tract, while those 

 from the fasciculus communis descend on the inner side of 

 this tract in the medulla and, turning outward, emerge below, 

 forming another of the components of this root. This is in 



