. Embryology. Embryology; Embryology; genealogy. 174 EMBRYOLOGY FOLDS OF AMNION. YOLK SAC Fig. 102. The folds of the amnion, the allantois, and the circulation in an early chick embryo. The amnion: The head fold advances posteriorly and a tail fold forms. It grows forward and finally meets the head fold. The folds are drawn as a single line but are actually a fused layer of ectoderm and mesoderm. The allantois: A saclike structure lined with endoderm and covered with mesoderm. The umbilical veins and arteries develop in the mesoderm of the allantois. The circulation: Note three distinct parts:
. Embryology. Embryology; Embryology; genealogy. 174 EMBRYOLOGY FOLDS OF AMNION. YOLK SAC Fig. 102. The folds of the amnion, the allantois, and the circulation in an early chick embryo. The amnion: The head fold advances posteriorly and a tail fold forms. It grows forward and finally meets the head fold. The folds are drawn as a single line but are actually a fused layer of ectoderm and mesoderm. The allantois: A saclike structure lined with endoderm and covered with mesoderm. The umbilical veins and arteries develop in the mesoderm of the allantois. The circulation: Note three distinct parts: an embryonic circulation with its dorsal aorta and cardinal veins; a yolk-sac circulation with a flow of blood from the vitelline arteries into the vitelline veins; the allantoic circulation from um- bilical arteries to umbilical veins. growth of the hindgut. The allantois is covered with mesoderm which carries blood vessels—the umbilical arteries and veins (Fig. 102). During later development the allantois grows in between the chorion and the yolk sac and becomes highly vascular. Oxygen reaches the blood in the allantois after passing through a porous shell, shell membranes, the chorion, and the walls of the blood vessels in the allantois. The fused membrane of the allantois and chorion is called the chorioallantoic membrane. It is an excellent site for the growth and differentiation of isolated parts of the embryo. The isolated limb bud of the chick embryo has been transplanted to the chorioallantoic membrane to test its ability to self-differentiate. During the formation of both the yolk sac and the allantois the splanchnic layer of the lateral mesoderm remains in close contact with the endoderm, and for this reason the two layers are called the 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 origina
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Keywords: ., boo, bookcentury1900, booksubjectembryology, booksubjectgenealogy
