Fig. 54 Part of a horizontal section (slightly inclined with the right side 

 farther dorsal) through the medulla oblongata of larval Amblystoma tigrinum 54 

 mm. long; silver impregnation method of Ram6n y Cajal. X 100. The fibers of 

 the mesencephalic V root are seen near the superficial origin of the V roots, where 

 the}^ separate from the spinai V root to turn inward and forward across the ros- 

 tral aspect of the motor V nucleus. The positions of the motor V and motor 

 VII nuclei are indicated on the drawing, though the cells of these nuclei lie 

 immediately dorsally of the plane here figured. The entire region between the 

 V and VII roots in this preparation is filled with arcuate fibers, which have not 

 been sketched in the figure. The fibers of the mesencephalic V root are coarser 

 than any others of this region and can be readily distinguished. They are seen to 

 give off equally coarse collateral branches which terminate in the motor VII 

 nucleus. In some of our sections much finer branches of these fibers are seen to 

 terminate in the motor V nucleus, but these are not visible in this preparation. 



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THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 24, NO. 4 



