. The Journal of comparative neurology and psychology. in doubt. Thesection passes through the sensory root near its exit and through themotor nucleus. As is well known, the bundles of the motor root,starting from their nucleus, are directed more cephalad than thesensory root and so pass beneath the sensory root to emerge on thesurface of the pons cephalad from it. In this section the sensoryroot is cut lengthwise as it pierces the pons in nearly the transverseplane. In sections just behind this the sensory root turns caudad asthe spinal trigeminal tract. Since the motor root runs diagonally 6
. The Journal of comparative neurology and psychology. in doubt. Thesection passes through the sensory root near its exit and through themotor nucleus. As is well known, the bundles of the motor root,starting from their nucleus, are directed more cephalad than thesensory root and so pass beneath the sensory root to emerge on thesurface of the pons cephalad from it. In this section the sensoryroot is cut lengthwise as it pierces the pons in nearly the transverseplane. In sections just behind this the sensory root turns caudad asthe spinal trigeminal tract. Since the motor root runs diagonally 622 Journal of Comparative Neurology and Psychology. cephalad its bundles are cut obliquely and reach in this section onlyas far as the internal or dorsal border of the pons. The outline ofthe motor nucleus is indicated by a dotted line and it is evident thatthe greater part of the motor root comes from this nucleus. Dorsalto the nucleus are seen fibers passing over it and turning downparallel with the motor bundles. In adjacent sections it is clearly. Fig. 19. Human foetus, 27 cm. Transverse section of the trigeminal roots onthe left side. Weigert stain, x 25. Camera drawing. seen that these fibers form definite bundles which go out with themotor root. They are the crossed fibers of the motor are all the fibers which enter the motor root in this mesencephalic root continues in the transverse plane from thesensory root to a point dorsal to the motor nucleus, where it turnsforward to go through the isthmus to the tectum mesencephali. Theoonnection of the mesencephalic bundle with the sensory root in this Johnston, The Radix Mesencephalica Trigemini. 623 section is unmistakable, since both lie in the plane of the transversesection and the mesencephalic fibers run directly among the sensorybundles. The motor bundles are crossing the mesencephalic bundleobliquely. In the sections caudal to this one, other fasciculi of the % ill ly ? HI ^/^
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