6l6 "Journal of Comparative Neurology and Psychology. 



fibers probably arise from cells of the locus coeriileiis, as in the caudal 

 part of the locus coeruleus in the rat a considerable part of the large 

 cells send their large processes caudad away from the trigeminal 

 bundle (Fig. 4B). 



There are two great advantages in the study of the l)uiidlo in 



mesenc 



velum 



cdim 



Vmot 

 Vsens. 



Fiu. lo. A model of the right half of the brain of the human embryo 11. 1!). 

 from the level of the Vllth nerve to that of the Hid nerve. A, from the 

 medial surface ; B, from the lateral surface. The sulcus limitaus is indicated 

 by a dotted black line, and ou the outer surface and on the trigeminus the 

 boundary line between sensory and motor structures is indicated in the same 

 way. The radix mesencephalica runs dorsal to the sulcus limitans through 

 its whole course. 



embryonic brains. First is the simplicity (if structure which enables 

 one to trace the bundle Avith perfect ease and certainty. Second is 

 the clearness of the general morphological relations. It is easy to 

 determine whether the mesencephalic root and its nucleus of origin 

 lie in the sensory or in the motor zone of the l)rain. I was fortunate 

 to receive in 1905 a human embryo which measured after fixation 



