. The elements of embryology. Embryology; Embryology. X.] PKIMITIVE STREAK. 319 todermic vesicle is therefore formed of three areas, (1) the embryonic area with two layers, a columnar epiblast and flat hypoblast; (2) the region around the embryonic area where the walls of the vesicle are formed of flattened epiblast^ and of hypoblast; (3) the area beyond this again where the vesicle is formed of flat- tened epiblast^ only. The changes which next take place begin with the formation of a primitive streak, homologous with, and in most respects similar to, the primitive streak in Birds. EiG.
. The elements of embryology. Embryology; Embryology. X.] PKIMITIVE STREAK. 319 todermic vesicle is therefore formed of three areas, (1) the embryonic area with two layers, a columnar epiblast and flat hypoblast; (2) the region around the embryonic area where the walls of the vesicle are formed of flattened epiblast^ and of hypoblast; (3) the area beyond this again where the vesicle is formed of flat- tened epiblast^ only. The changes which next take place begin with the formation of a primitive streak, homologous with, and in most respects similar to, the primitive streak in Birds. EiG. Embryonic Area of an Eight Days' Eabbit. (After KoUiker.) arg. embryonic area ; pr. primitive streak. The formation of the streak is preceded by that of a dark spot near the middle of the blastoderm, forming the nodal point of Hensen. This spot subsequently constitutes the front end of the primitive streak. Early on the seventh day the embryonic area be- comes pyriform, and at its posterior and narrower end 1 The epiblast of the blastodermic vesicle beyond the embryonio area is formed of the outer layer Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Foster, M. (Michael), Sir, 1836-1907; Balfour, Francis M. (Francis Maitland), 1851-1882; Sedgwick, Adam, 1854-1913; Heape, Walter, 1855-1929. London : Macmillan and Co.
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Keywords: ., bookcentury1800, bookdecade1, booksubjectembryology, bookyear1883
