. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. FORMATION OF PROTECTIVE EMBRYONIC MEMBRANES 909 AMNION ALLANTOIS. SPLANCHNOPLEURE OF ALLANTOIC SAC EXTRA- EMBRYONIC MESODERM Fig. 370. Diagrams of extra-embryonic membranes. (A) Transverse section of yolk sac and developing body in teleost and elasmobranch fishes showing relation of body layers to the yolk mass. (B) Transverse section of yolk sac and forming serosa (chorion) in reptiles, birds, and prototherian mammals. (C-E) Diagrams showing extr
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. FORMATION OF PROTECTIVE EMBRYONIC MEMBRANES 909 AMNION ALLANTOIS. SPLANCHNOPLEURE OF ALLANTOIC SAC EXTRA- EMBRYONIC MESODERM Fig. 370. Diagrams of extra-embryonic membranes. (A) Transverse section of yolk sac and developing body in teleost and elasmobranch fishes showing relation of body layers to the yolk mass. (B) Transverse section of yolk sac and forming serosa (chorion) in reptiles, birds, and prototherian mammals. (C-E) Diagrams showing extra-embryonic membranes in the pig. (C) Conditions in 16-17 somite pig, age approximately 16 days. The ends of the diagram have been omitted in part, because of length of embryonic vesicle. (D) Conditions in embryo of 5 mm. or about 17-18 days of age. (E) The extra- embryonic membranes in embryo of about 4-5 weeks of age. derm and mesoderm, , the splanchnopleure, as the extra-embryonic coelom tends to separate the splanchnopleure from the somatopleure in these forms (fig. 370B). b. Amnion The amnion is a specialized sac which comes to encompass the embryo in reptiles, birds and mammals (fig. 370B-E). Because of its restriction to these vertebrates, the reptiles, birds and mammals are grouped together as the Amniota, the fishes and amphibia being designated as the Anamniota. Eggs which are spawned into the surrounding water, as in fishes and am- phibia, are cradled or cushioned by the surrounding fluid, and the embryo is free to develop without undue pressure from any side. In the Amniota, however, this watery environment must be established artificially and hence the amnion is formed to accommodate and enclose the fluid of this individ- ualized embryonic "swimming" 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 resem
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