. The Journal of comparative neurology and psychology. Fig. 23. Human foetus, 37 cm., frontal section througli the inferior coUiculusand isthmus. X 20. Description in the text. Johnston, The Radix Mesencephalica Trigemini. 629 fibers of the acustic area. In these figures the cells are removed fromthe motor nucleus by about the diameter of that nucleus itself. Thecells shown in Fig. 22 are the nearest cells to the motor nucleus. Foetus of 37 cm., horizontal or frontal sections. From this seriesnine sections are drawn (Figs, 23 to 32) showing the course of themesencephalic root from the mid-brai
. The Journal of comparative neurology and psychology. Fig. 23. Human foetus, 37 cm., frontal section througli the inferior coUiculusand isthmus. X 20. Description in the text. Johnston, The Radix Mesencephalica Trigemini. 629 fibers of the acustic area. In these figures the cells are removed fromthe motor nucleus by about the diameter of that nucleus itself. Thecells shown in Fig. 22 are the nearest cells to the motor nucleus. Foetus of 37 cm., horizontal or frontal sections. From this seriesnine sections are drawn (Figs, 23 to 32) showing the course of themesencephalic root from the mid-brain to its exit in the the purpose of demonstrating whether this bundle is connectedwith the motor or sensory root it will be best to follow it from abovedoAvnward in the description. In sections through the decussation. Fig. 24. The sixth section of this series (12 of the whole series presumably)ventral to that drawn in Fig. 23. x 20. Description in text. of the trochlearis the mesencephalic bundle is seen passing forwarddeep in the corpora quadrigemina, or rather along their base, andreaching nearly to the bundles of the posterior commissure. Cellsare seen at intervals along the bundle, twenty or more being countedin a single section on one side. A drawing of such a section has notbeen made because this part of the course of the bundle is familiarto every one. Fig. 23 shows a section of the mesencephalic bundlebeneath the posterior eolliculus at the point where it begins to turnventrally. Far forward appears the root of the trochlearis, to theleft is the lateral lemniscus, and between them is the brachium con- 630 Journal of Comparative Neurology and Psychology. jiinctivum whose fibers are lightly medullated. In Fig. 24 thegreater part of the fibers have turned ventrad and are cut across inthe secti
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