A system of obstetrics . ion proceed- and the blastoderm spreads over the yelk both areas increase in Bize. // is in the (trift pellucida thai the embryo develops. The Non-embryonle Portion of the Blastoderm,—The large food^yelk of the hen- egg, which, with the white, ha- to he absorbed and utilized for the nourishment of the embryo, ne-cessitates an extension of the blastodermfar beyond the region in which the embryoitself is formed. This is the rum-embryonicportion: it gives rise to accessory foetalstructures—the yelk-sac and the Primitive Streak and Groove.—After twelve hours of
A system of obstetrics . ion proceed- and the blastoderm spreads over the yelk both areas increase in Bize. // is in the (trift pellucida thai the embryo develops. The Non-embryonle Portion of the Blastoderm,—The large food^yelk of the hen- egg, which, with the white, ha- to he absorbed and utilized for the nourishment of the embryo, ne-cessitates an extension of the blastodermfar beyond the region in which the embryoitself is formed. This is the rum-embryonicportion: it gives rise to accessory foetalstructures—the yelk-sac and the Primitive Streak and Groove.—After twelve hours of incubation, whenthe whole blastoderm is not larger thana dime, surface views disclose a slightopacity in one portion of the area pel-lucida (Fig. 21). This opacity is the prim-itive streak. Sections show that it is due(Fig. 22) to a great thickening of the me-soblast in this region, caused by multipli-cation of epiblast cell-. The long axis of the primitive streak is at right angle- to the long axis of the egg, but. XI View of Area Pellucidaof Young Blastoderm of chick,showing first appearance of prim-itive streak (from Balfour): pellucida; , inner mar-gin of area opaca ; PRjS, primitivestreak. pr Fig. 22. Wr
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
