No. I.] THE CRANIAL NERVES OF AMPHIBIA. l8l 



in the ganglion cells of the central gray. It is here almost in 

 the extreme dorsal part and quite close to the ventricle. It 

 can be traced caudad into the spinal cord a short distance only, 

 in the adult frog. It lies then in the posterior columns close 

 to the median line. Judging from Weigert preparations it con- 

 tains in this portion only a very few medullated fibres. Accord- 

 ing to Golgi preparations in the tadpole there are few fibres 

 in it in this region (PL XI, Fig. 31). The remainder is made up 

 apparently, of a ''ground substance." The change in position 

 and character of this structure as we advance cephalad is well 

 shown in the Golgi preparations from which Figs. 31-39 

 inclusive were drawn. The tract gradually comes to lie further 

 ventrad and laterad and also increases in size. The number of 

 fibres in it, all fine and with a thin sheath or none, also 

 increases very greatly as shown both by the Golgi and Weigert 

 preparations. The maximum is reached at the level of the 

 exit of the second root of the IX + X, which, as we have 

 seen, derives a considerable portion of its fibres from the 

 fasciculus. Cephalad of this, it continues as a small bundle, 

 rather difficult to follow in the tadpole, until it passes out 

 in one of the facial roots as described above (p. 113, see also 

 Fig. 39). Whether a portion of it continues on still further 

 cephalad could not be ascertained in the tadpole. According 

 to Osborn (45), it does continue forward in Cryptobranchus. 

 As seen in the figures (31-39) its course is nearly parallel with 

 the ascending Trigeminus tract. Both undergo, on entering 

 the medulla, a downward deflection. Consequently, if the 

 ascending Trigeminus (and this tract t) represent morpho- 

 logically, in the medulla, the posterior columns of the cord, 

 the tracts and nuclei connected with the lateral line system 

 are superadded structures, inasmuch as they lie dorsal to these. 

 (Compare Ahlborn on Petromyzon.) 



As the fasciculus communis retreats from the immediate 

 vicinity of the ventricle or, rather, central, canal and from the 

 mass of cells surrounding the latter in the tadpole, a number 

 of the cells are detached with it and form a group on its inner 

 ventral side. This group of small cells, as shown in ordinary 

 carmine preparations, accompanies the fasciculus throughout 



