. The Journal of comparative neurology and psychology. shes, amphibians and reptiles. The relation of the mesencephalic bundle to the cerebellar fibersof the trigeminus is shown in three other sketches (Figs. 16, lY, 18)taken from sections between those drawn in Figs. 14, A and sketches show that in the early embryo the mesencephalicbundle is intimately associated with the ascending sensory root ofthe trigeminus, as was to be expected from its relations in lowervertebrates. It is also evident from all these figures that in theyoung embryo the mesencephalic bundle has not the remotest a
. The Journal of comparative neurology and psychology. shes, amphibians and reptiles. The relation of the mesencephalic bundle to the cerebellar fibersof the trigeminus is shown in three other sketches (Figs. 16, lY, 18)taken from sections between those drawn in Figs. 14, A and sketches show that in the early embryo the mesencephalicbundle is intimately associated with the ascending sensory root ofthe trigeminus, as was to be expected from its relations in lowervertebrates. It is also evident from all these figures that in theyoung embryo the mesencephalic bundle has not the remotest apparentrelation to the motor root or nucleus. That these relations becomeso greatly modified in the adult is due to a number of influencesamong which are probably the great growth of the cerebellum andthe vestibular nuclei related to it and the great size of the corpusrestiforme, all of which tend to crowd the sensory bundles of thetrigeminus closer to the motor nucleus. Another important factor is 620 Journal of Comparative Neurology and Fig. 18. V mdtFigs. 16, 17, 18. Three camera sketches of transverse sections of the brainof the embryo H. 19 tal^en between the levels of the sections shown in Fig. 14A and B. Fig. 16 is just in front of Fig. 14 A, and Figs. 17 and 18 arerespectively five and ten sections farther forward. These sections show theintimate relation of the mesencephalic bundle to the cerebellar fibers of thetrigeminus. |oHNSTON, Tlje Radix Mesencephalica Trigrniiiii. 621 probably found in the collateral branches from the mesencephaliclibers which enter the motor nucleus. In the pig embryos the course of the mesencephalic bundle hasbeen found to be identical with that in the human embryo describedabove. Through the courtesy of Professor Harlow Gale I have had theopportunity to study preparations of fa^tal brains of 27, 37 and 42cm. These are Weigert preparations made in Hiss laboratory atLeipzig in 1897 for the embryological study of liber tracts after
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