The development of the human body; a manual of human embryology . nd in the other ventricles. Owing to the very considerable size reached by thethickening of the lamina terminalis whose history has justbeen described, important changes are wrought in theadjoining portions of the mesial surface of ___J~_ dg the hemispheres. Be-fore the developmentof the thickening thegyrus dentatus andthe hippocampus ex-tend forward into theanterior portion ofthe hemispheres (), but on accountof their position theybecome encroachedupon by the enlarge-ment of the laminaterminalis, with theresult that the
The development of the human body; a manual of human embryology . nd in the other ventricles. Owing to the very considerable size reached by thethickening of the lamina terminalis whose history has justbeen described, important changes are wrought in theadjoining portions of the mesial surface of ___J~_ dg the hemispheres. Be-fore the developmentof the thickening thegyrus dentatus andthe hippocampus ex-tend forward into theanterior portion ofthe hemispheres (), but on accountof their position theybecome encroachedupon by the enlarge-ment of the laminaterminalis, with theresult that the hippo-campus becomes practically obliterated in that portion-of its course which lies in the region occupied by the cor-pus callosum, its fissure in this region becoming knownas the callosal fissure, while the corresponding portionsof the dentate gyrus become reduced to narrow and in-significant bands of nerve-tissue which rest upon the uppersurface of the corpus callosum and are known as the striaof Lancisi. The Olfactory Lobes.—At the time when the cerebral. Fig. 229.—Median Longitudinal Sec-tion of the Brain of an Embryo ofthe Fifth Month. ac. Anterior commissure; cc, corpus cal-losum ; dg, dentate gyrus; /, fornix;i, infundibulum; mc, middle commis-sure; si, septum lucidum; vi, veluminterpositum.—{Mihalkovicz.) 428 THE DEVELOPMENT OF THE HUMAN BODY. hemispheres begin to enlarge—that is to say, at about thefourth week—a slight furrow, which appears on the ven-tral surface of each anteriorly, marks off an area which,continuing to enlarge with the hemispheres, graduallybecomes constricted off from them to form a distinctlobe-like structure, the olfactory lobe (Fig. 217, VI 3). Inmost of the lower mammalia these lobes reach a veryconsiderable size, and consequently have been regardedas constituting an additional division of the brain, knownas the rhinencephalon, but in man they remain smaller,and although they are at first hollow, containing pro-longations from the la
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
