. Quain's elements of anatomy . Eig. i_7jr /^.s Fig. 635.—Transparekt area of the blastoderm of a chick at a very early period, SHOWING THE COMMENCEMENT OF THE PRIMITIVE STREAK. (FrOUl BalfoUr.) 2}, primitive streak ; «.j;, area pellucida ; , area opaca. Fig. 636.—Piriform transparent area of the chicks blastoderm with the primitiveGROOVE. (From Balfour.)2w, primitive streak and groove; a/, amniotic fold commencing; the darker shadinground the primitive streak indicates the extension of mesoblast. and en that side of the oval which afterwards becomes the narrow endof the pyriform

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. Quain's elements of anatomy . Eig. i_7jr /^.s Fig. 635.—Transparekt area of the blastoderm of a chick at a very early period, SHOWING THE COMMENCEMENT OF THE PRIMITIVE STREAK. (FrOUl BalfoUr.) 2}, primitive streak ; «.j;, area pellucida ; , area opaca. Fig. 636.—Piriform transparent area of the chicks blastoderm with the primitiveGROOVE. (From Balfour.)2w, primitive streak and groove; a/, amniotic fold commencing; the darker shadinground the primitive streak indicates the extension of mesoblast. and en that side of the oval which afterwards becomes the narrow endof the pyriform space, and therefore near the margin, a sickle-shapedopacity appears (Kupffer, jSTo. 113), which is gTadually prolongedinto the middle of the area and even beyond it, and as the marginalAvidening contracts, the whole takes the appearance of a strap-likethickening of nearly uniform diameter throughout. This is the lyrimi-tlve streak or trace, which is the first indication of the lineamentsof the future embryo. A groove very soon appe

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Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy