The development of the human body; a manual of human embryology . to the pulvinar of the thalamus and to an externalgeniculate body, and two ridges extending backward anddorsally from the latterstructures to the thicken-ings in the roof of the mid-brain which represent theanterior corpora quadri-gemina, give a path alongwhich the nerve-fiberswhich constitute the ante-rior brachia pass. From the ventral zoneswhat is known as the sub-thalamic region develops, amass of fibers and cellswhose relations and devel-opment are not yet clearlyunderstood, but which maybe regarded as the forwardcontinuati
The development of the human body; a manual of human embryology . to the pulvinar of the thalamus and to an externalgeniculate body, and two ridges extending backward anddorsally from the latterstructures to the thicken-ings in the roof of the mid-brain which represent theanterior corpora quadri-gemina, give a path alongwhich the nerve-fiberswhich constitute the ante-rior brachia pass. From the ventral zoneswhat is known as the sub-thalamic region develops, amass of fibers and cellswhose relations and devel-opment are not yet clearlyunderstood, but which maybe regarded as the forwardcontinuation of the teg-mentum and reticular for-mation. In the median lineof the floor of the ventriclean unpaired thickening ap-pears, representing the cor-pora albicantia, which dur-ing the third month be-comes divided by a medianfurrow into two roundedeminences; but whetherthese structures and theposterior portion of the tuber cinereum, which also de-velops from this region of the brain, are derivatives ofthe ventral zones or of the floor-plate is as yet Fig. 223.—Dorsal View of theBrain, the Roof op the Lat-eral Ventricles being Re-moved, of an Embryo of MM. b, Anterior brachium; eg, externalgeniculate body; cp, chorioidplexus; cqa, anterior corpusquadrigeminum; /(, hippocam-pus ; hf, hippocampal fissure; ot,optic thalamus; p, pineal body;rp, roof-plate.—(His.) 418 THE DEVELOPMENT OF THE HUMAN BODY. Assuming that the albicantia and the tuber cinereum arederived from the ventral zones, the origins of the structuresformed from the walls of the diencephalon may be tabulated asfollows: Roof-plate, J ™m interpositum I Epiphysis. r Optic zones, -j Pulvinares. y External geniculate bodies. {Subthalamic cinereum (in part).Floor-plate, Tissue of mid-ventral line. The Development of the Telencephalon.—For convenienceof description the telencephalon may be regarded as con-sisting of a median portion, which contains the a
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
