. The Journal of comparative neurology and psychology. 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 mese
. The Journal of comparative neurology and psychology. 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 ^/^. Fig. 20. Section next anterior to that sliown in Fig. 19. An interlacing ofthe mesencephalic fibers with the crossed motor fibers. The two form with thesensory root a Y-shaped figure. The mesencephalic fibers descend among thesensory fibers in the stem of the Y, while the motor fibers in their obliquecourse forward leave the section at the point where the two bundles interlace. mesencephalic bundle are cut lengthwise and show exactly the samerelations as are seen in this section. In the section next cephaladthere is an interlacing of the fibers of the crossed motor root withthe most cephalic fibers of the mesencephalic bundle. As this is the 624 Journal of Comparative Neurology and Psychology. point at which all the confusion of the two kinds of fibers arises, thissection is drawn in Fig. 20. The motor roots are cut obliquely, thesensory root is cut nearer to its point of exit. The crossed motorbundle crosses the mesencephalic bundle at such an angle that thetwo kinds of fibers can be
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