Johnston, The Radix Mesei^cephahca Trigemini. 627 



as those pass downward and forward beneath it. In sections caudal 

 to those shown in these figures the same relations maintain, except 

 that the mesencephalic bundle is more widely separated from the 

 motor bundles in successive sections. It is seen in Fig. 21 that fibers 

 pass out from the mesencephalic bundle to end in the sensory nucleus. 

 The close relation of this bundle to the sensory nucleus is clearer in 

 the next sections caudad. Here it is distinctly seen that the mesen- 

 cephalic bundle runs through the sensory nucleus and in the case of 

 many sensory fibers it is difficult to tell whether they accompany the 

 bundle or end in the sensory nucleus. Also it appears that many 

 sensory root fibers run through the lateral part of the sensory nucleus 

 or over its lateral surface and continue parallel with the mesen- 

 cephalic bundle to enter the cerebellum. Some of these relations are 

 shown in Fig. 22, which is taken from the second section in this 

 series caudal to the one sho\vii in Fig. 21. In the sections next 

 cephalad from those figured, the same interlacing of mesencephalic 

 fibers wdth decussating motor fibers as was seen in the 27 cm. foetus 

 is present and gives a confused picture. This interlacing is difficult 

 to unravel in transverse sections because of the greater number of 

 fibers medullated as compared with the younger stage and a drawing 

 of this would not be clear unless it were made diagi-ammatic by 

 omitting many of the fibers. The study of the sections convinces me 

 that there is only an interlacing together with a certain crowding, as 

 compared with the. younger foetus, and that the mesencephalic fibers 

 all join the sensory root. From the horizontal sections next to be 

 described this interlacing is drawn as accurately as possible under 

 the camera without any schematizing, and the evidence for the con- 

 clusion here stated will be seen in those figures. It should be borne 

 in mind, however, that in both the series of transverse sections above 

 described the greater part of the mesencephalic root clearly passes 

 down to the sensory root wholly separate from the motor root, so that 

 any doubt that might exist regarding its possible relation to the 

 motor root would attach to only the small part of its fibers. 



The cells of the mesencephalic root are drawn in black in Figs. 21 

 and 22. It is clearly seen here that these cells are separated from 

 the motor nucleus liv the motor root bundles and bv the arcuate 



