Johnston, The Radix Mesencepbahca Trigemim. 60 1 



stellare and Squalus acanthias show as clearly as may be desired the 

 entrance of the large processes of these cells into the bundles of the 

 radix mesencephalica trigemini and the appearance of a sheath on each 

 such fiber a short distance from the cell (Figs. 1, 2 and 3). This 

 is seen in a very large number of cells and it is only the circuitous 

 course often taken by the large processes which makes it difficult to 

 demonstrate. The drawings are taken from Weigert sections in 

 which the sheaths are perfectly fixed and stained while the cells and 

 processes are stained by acid fuchsin. The bundles of fibers belong- 



FiG. 3. 



Fig. 2. 

 Fig. 2. Squalus aeauthias, sliowiug the same as Fig. 1. 



Fig. 3. Squalus acanthias, showing the same as Fig. 1. a, h, c. three cells, 

 parts of which are cut away In the section. 



ing to this root in selachians are so distinct from all other fibers that 

 there can be no doubt that the processes of the large cells actually 

 become fibers of this root. The same has been clearly demonstrated 

 in sections of the sturgeon ])rain not used for the previous study. 



The origin of the fibers has been seen in the toad and will be de- 

 scribed in the following section. In the rat, mouse and rabbit they 

 have been studied in sections prepared by the Cajal and Eielschowsky 

 silver methods, and it need only be said that the description by Cajal 

 is confirmed (Figs. 4 and 5). 



