. The Journal of comparative neurology and psychology. motor root or to find goodreason for doubting its connection with the sensory root. Instead of burdening the paper with an extended description andwith numerous figures of the various brains, I will make one or twonotes on the course of the bundle in adult brains and depend upon thefigures from the human embryonic and icctsil brains to demonstratethe essential relations in mammals. It is necessary to give attentiononly to the relations of this bundle to the motor and sensory roots,since the course of the upper part of the bundle is well un
. The Journal of comparative neurology and psychology. motor root or to find goodreason for doubting its connection with the sensory root. Instead of burdening the paper with an extended description andwith numerous figures of the various brains, I will make one or twonotes on the course of the bundle in adult brains and depend upon thefigures from the human embryonic and icctsil brains to demonstratethe essential relations in mammals. It is necessary to give attentiononly to the relations of this bundle to the motor and sensory roots,since the course of the upper part of the bundle is well understood. 614 Journal of Comparative Neurology and Psychology. The first mammal in which the bundle was followed with certaintywas the mole, whose brain is comparatively simple and it the bundle runs caudad over the motor nucleus without anycomplex relation to it and then bends downward and forward toenter the spinal trigeminal tract and leave the brain in the sensoiyroot. The large cells in the locus coeruleus are widely separated from. C Fig. 12. Sketches to show the course of the meseucephalic root in thecommou rat. A, B, C, camera outlines from transverse sections; D, diagramof the roots projected on the sagittal plane. In A, the mesencephalic bundlebends down through the substantia gelatinosa to enter the spinal trigeminaltract. Its fibers then run forward to leave the brain in the sensory root (C). the motor nucleus and closely related to the granular layer of thecerebellum. I hope to study and describe this relation later, but itis to be noted here that there is nothing to suggest any relation ofthe locus coeruleus to the motor nucleus of the trigeminus or to anyother motor area. The essential features seen in the mole gave the key to the studyof other mammals. In the rat (Fig. 12) and cat it was found Johnston, The Radix Mesencephalica Trigennni. 615 that although the bundle traverses the upper surface of the motornucleus much more closely than in the mole
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