. A laboratory manual and text-book of embryology. Embryology. EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 87 77). The dorsal convexity is probably abnormal. A robust body-stalk attaches the embryo to the inner wall of the chorion. With the growth of the head- and tail-folds of the embryo, there is an apparent constriction of the yolk-sac where it joins the em- bryo. This will become more marked in later stages and form the yolk-stalk. His's embryo, mm. long, shows the relative size of yolk-sac and embryo and the yolk-stalk (Fig. 78). The relations of the fetal membranes to the embryo arc much
. A laboratory manual and text-book of embryology. Embryology. EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 87 77). The dorsal convexity is probably abnormal. A robust body-stalk attaches the embryo to the inner wall of the chorion. With the growth of the head- and tail-folds of the embryo, there is an apparent constriction of the yolk-sac where it joins the em- bryo. This will become more marked in later stages and form the yolk-stalk. His's embryo, mm. long, shows the relative size of yolk-sac and embryo and the yolk-stalk (Fig. 78). The relations of the fetal membranes to the embryo arc much the same as in the chick embryo of five days, save that the allantois of the human embryo is embedded in the body-stalk. The embryo shows a regular convex dorsal curvature, there is a marked cephalic bend in the region of the mid-brain and there are three gill clefts. The head is twisted to the right, the tail to the. Fig. 77.—Human embryo at the commencement of the third week (from His, after Coste). X 15. A, inner or true amnion; , body-stalk; //, heart; V, blood-vessel on yolk-sac; , yolk-sac. Amnion Branchial clefts 1-3 Body-stalk Maxillary process Mandibular process Heart. 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 Prentiss, Charles William, 1874-1915. Philadelphia, London, W. B. Saunders
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