The development of the human body; a manual of human embryology . rise to the solitary fasciculus of adult anatomy, andin embryos of 11 to 13 mm. it becomes covered in by thefusion of the reflected lip of the dorsal zone with the sidesof the myelencephalon, this fusion, at the same time,drawing the margins of the roof-plate ventrally to form asecondary lip (Fig. 219). Soon after this a remarkable mi-gration ventrally of neuroblasts of the dorsal zone rapidly in number the migrating cells pass on THE MYELENCEPHALON. 409 either side of the solitary fasciculus toward the territo
The development of the human body; a manual of human embryology . rise to the solitary fasciculus of adult anatomy, andin embryos of 11 to 13 mm. it becomes covered in by thefusion of the reflected lip of the dorsal zone with the sidesof the myelencephalon, this fusion, at the same time,drawing the margins of the roof-plate ventrally to form asecondary lip (Fig. 219). Soon after this a remarkable mi-gration ventrally of neuroblasts of the dorsal zone rapidly in number the migrating cells pass on THE MYELENCEPHALON. 409 either side of the solitary fasciculus toward the territory ofthe ventral zone, and, passing ventrally to the ventralportion of the mantle layer, into which fibers have pene-trated and which becomes the formatio reticularis (, />•), they differentiate to form the olivary body (ol). The thickening of the floor-plate gives opportunity forfibers to pass across the median line from one side to theother, and this opportunity is taken advantage of at anearly stage by the axis-cylinders of the neuroblasts of the. Fig. 219.—Transverse Section through the Medulla Oblongata op an Embryo of about Eight , Ascending root of the trigeminus; [r, reticular formation; ol, olivary body; sf, solitary fasciculus; tr, restiform body; XII, hypoglossal nerve.—(His.) ventral zone, and later, on the establishment of the olivarybodies, other fibers, descending from the cerebellum, de-cussate in this region to pass to the olivary body of theopposite side. In the lower part of the medulla fibersfrom the neuroblasts of the nuclei of Goll and Burdach,which seem to be developments from the mantle layer ofthe dorsal zone, also decussate in the substance of thefloor-plate; these fibers, known as the arcuate fibers, pass inpart to the cerebellum, associating themselves with fibersascending from the spinal cord and with the olivary fibers 4-IO THE DEVELOPMENT OF THE HUMAN BODY. to form a round bundle situated in the dorsal portion ofthe margina
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
