. Human embryology and morphology. Embryology, Human; Morphology. 274 HUMAN EMBRYOLOGY AND MORPHOLOGY. and formation of the cord, comes to lie on the placenta (Fig. 222). The neck of the yolk sac, the vitello-intestinal duct, lies within the umbilical cord. By the sixth week the sac is in a state of coeliao axis left colic inf. mes. sup. intest. loop placenta yolk sac Flo. 222.—The Form of the Alimentary Canal during the 5th week. retrogression. The U-shaped intestinal loop, which is formed from the mid-gut, is at first really extra-abdominal, being situated within a funnel-shaped cavit
. Human embryology and morphology. Embryology, Human; Morphology. 274 HUMAN EMBRYOLOGY AND MORPHOLOGY. and formation of the cord, comes to lie on the placenta (Fig. 222). The neck of the yolk sac, the vitello-intestinal duct, lies within the umbilical cord. By the sixth week the sac is in a state of coeliao axis left colic inf. mes. sup. intest. loop placenta yolk sac Flo. 222.—The Form of the Alimentary Canal during the 5th week. retrogression. The U-shaped intestinal loop, which is formed from the mid-gut, is at first really extra-abdominal, being situated within a funnel-shaped cavity formed by the somatopleure at the umbilicus. The vitelline artery, afterwards the superior mesenteric, is the artery of the TJ-shaped loop; it terminates at the vitello- intestinal canal—the elongated neck of the yolk sac (Fig. 2 2 2). Persistence of Certain Embryonic Structures.—Many of the features seen in the human embryo at the stage of development reached during the fifth or sixth weeks may persist. 1. The most common structure to remain is the intestinal end of the neck of the yolk-sac—Meckel's diverticulum. It occurs in 2 per cent, of subjects, and commonly forms a finger- glove-like sac on the free border of the ileum about four feet above the ileo-caecal valve. Hence we know that this part of the ileum forms the apex of the U-shaped loop of intestine. 2. The neck of the yolk sac, instead of closing, may remain open at the umbilicus and form a faecal fistula at 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 Keith, Arthur, Sir, 1866-1955. London : E. Arnold
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
