The development of the human body; a manual of human embryology . Fig. 28.—Suctions of Ova of a Bat showing (A) the Formation ofthe Endoderm and (B and C) of the Amniotic Cavity.—{VanBeneden.) the ovum is now formed of three layers, an outer onewhich may be termed the trophoblast, a middle one which THE FORMATION OF THE GERM LAYERS. 73 probably is transformed into the extra-embryonic meso-derm of later stages, though its significance is at presentsomewhat obscure, and an inner one which is the primaryendoderm. In the bat, of whose ovum Fig. 28, C, repre-sents a section, that portion of the mid
The development of the human body; a manual of human embryology . Fig. 28.—Suctions of Ova of a Bat showing (A) the Formation ofthe Endoderm and (B and C) of the Amniotic Cavity.—{VanBeneden.) the ovum is now formed of three layers, an outer onewhich may be termed the trophoblast, a middle one which THE FORMATION OF THE GERM LAYERS. 73 probably is transformed into the extra-embryonic meso-derm of later stages, though its significance is at presentsomewhat obscure, and an inner one which is the primaryendoderm. In the bat, of whose ovum Fig. 28, C, repre-sents a section, that portion of the middle layer whichforms the roof of the amniotic cavity disappears, only the. Fig. 29.—A, Side View of Ovum op Rabbit Seven Days Old (Kolliker); B, Embryonic Disk op a Mole (Heape); C, Embryonic Disk op a Dogs Ovum of about Fifteen Days {Bonnet),ed, Embryonic disk; hn, Hensens node, mg, medullary groove; ps,primitive streak; to, vascular area. trophoblast persisting in this region, but in another formthis is not the case, the roof of the cavity being composedof both the trophoblast and the middle layer. A rabbits ovum in which there is yet no amniotic cavityand no splitting of the enveloping layer shows, whenviewed from above, a relatively small dark area on thesurface, which is the embryonic disk. But if it be looked 74 THE DEVELOPMENT OF THE HUMAN BODY. at from the side (Fig. 29, A), it will be seen that the upperhalf of the ovum, that half in which the embryonic diskoccurs, is somewhat darker than the lower half, the line ofseparation of the two shades corresponding with the edgeof the primary endoderm which has extended so far in itsgrowth around the inne
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
