. The chordates. Chordata. 292 Basic Structure of Vertebrates. Fig. 241. Diagram of the fetal structures of a mammal. Sagittal section. The broken lines represent mesoderm. (A) Amnion; (AL) cavity of allantois; (B) brain; (C) chorion; (E) enteron; (EX) extra-embryonic coelom; (H) heart; (NC) noto- chord; (NT) neural tube; (P) placental region of allantois and chorion; (SM) somatopleure; (SP) splanchnopleure; (V) chorionic villi; (YS) cavity of yolk-sac. (Courtesy, Neal and Band: "Chordate Anatomy," Philadelphia, The Blakiston Company.) or embryonic body-wall (Figs. 239, 240). The emb
. The chordates. Chordata. 292 Basic Structure of Vertebrates. Fig. 241. Diagram of the fetal structures of a mammal. Sagittal section. The broken lines represent mesoderm. (A) Amnion; (AL) cavity of allantois; (B) brain; (C) chorion; (E) enteron; (EX) extra-embryonic coelom; (H) heart; (NC) noto- chord; (NT) neural tube; (P) placental region of allantois and chorion; (SM) somatopleure; (SP) splanchnopleure; (V) chorionic villi; (YS) cavity of yolk-sac. (Courtesy, Neal and Band: "Chordate Anatomy," Philadelphia, The Blakiston Company.) or embryonic body-wall (Figs. 239, 240). The embryo becomes com- pletely surrounded by such a fold, which then grows in centripetally from all directions and finally encloses the embryo. Where opposite edges of the fold meet above the embryo, they coalesce. Reference to Figs. 239 and 241 will serve better than description to make clear the resulting relations of layers and spaces. The somatopleural folds which give rise to the amnion and chorion are, at the time of their formation, a living part of the embryo. The statement that the folds eventually enclose the embryo anticipates the fact that the amnion and chorion do not become any part of the adult. Therefore "the embryo" which the folds enclose is the definitive body region of the embryo. Everything else is conveniently referred to as extra-embryonic. The allantois, an outgrowth from the hind region of the enteron (Figs. 239, 241), is a product of the splanchnopleure and therefore lined by endoderm. Becoming extensively fused with the chorion, the apposed mesodermal layers of the two membranes develop a rich net-. 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 Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakiston
Size: 1673px × 1494px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollect, bookpublisherphiladelphiablakiston
