320 G. E. COGHILL 



Fig. 33 Coiled-reaction stage (No. 561, section 1-3-14). X 500. The plane • 

 of section is shown in figure 17, in which the region of this figure is included 

 between the lines and indicated by a. The caudal end of the figure is to the left, 

 and is a great deal farther dorsad than is the rostral or right end of the figure. 

 The root of the trigeminal nerve {R.V) here approaches the brain in two divi- 

 sions, the root from the Gasserian ganglion (R.G.G.) and that of the ophthalmic 

 ganglion (R.oph.). The latter is entering the brain and bifurcating into a short 

 ascending tract (Tr.Asc.V) and a massive descending tract {Tr.Des.V). In the 

 angle of this bifurcation is a large neurone {D.C.), the very large nucleus of which 

 is in sharp contrast with the surrounding nuclei. This cell lies in the dorso- 

 ventral level of the sensory root and is far removed from the motor nucleus, 

 several cells of which can be recognized in a more ventral position {Nuc. vis. m.). 



Fig. 34 Coiled-reaction stage (No. 562, section 1-4-2). X 500. This is from' 

 a transverse section located 56 fx rostrad of the entrance of the trigeminal root. 

 It shows the presence at this level of ascending root fibers of this nerve {Tr.Asc.V). 

 In a more dorsal position there is a cell of the Rohon-Beard type {D.C.) which 

 has a long process extending into the immediate vicinity of or actually into the 

 ascending trigeminal tract. 



Figs. 35 to 37 Coiled-reaction stage (No. 562, sections 1-4-9, 10 and 11). 

 X 500. Three successive transverse sections through the brain at the entrance 

 of the trigeminal root {R.V). 



Figure 35 is the most rostral in position, and shows two or three cells of the 

 type described in the last two figures {D.C). Another cell of this type appears 

 in figures 36 and 37 {D.C), two sections through the same cell. In both figures 

 the peripheral process of the cell is shown entering the trigeminal root. In figure 

 37 there is a stump of a dorsally directed process, and in figure 36, evidence of a 

 ventrally directed process. Cells of the root mass {R.M.) appear in all these 

 fioures. 



