JOHNSTON, The Radix Mesencephaltca Trtgemini. 617 



in formalin 15.5 mm. The embryo is small for its stage of devel- 

 opment. The specimen was so fresh that the tissnes show an almost 

 perfect histological fixation and the l)rain is in excellent condition 



Fig. 14. Camera outliues of four transverse sections through the hrain of 

 the embryo II. 19. These sketches show the course of the mesencephalic bundle 

 from the sensory root to the level of the trochlearis. Note its relations to the 

 sulcus limitans, the two arms of the trochlearis and the tr. tecto-cerebellaris. 



for stndy. The specimen was cnt in a perfect series of frontal sec- 

 tions 10 microns in thickness and stained in Delafield's hgematoxylin. 

 The bundle can be traced readily in this embryo with either high or 



