. The development of the chick; an introduction to embryology. Birds -- Embryology. 144 THE DEVELOPMENT OF THE CHICK arises from the neck of the allantois both behind and also at the sides, (cf. Fig. 82.) During the fourth day the distal portion of the allantois pushes out into the portion of the extra-embryonic body-cavity beneath the hind end of the embryo and rapidly expands to form a relatively large sac. But the neck of the allantois remains embedded in the ventral mesentery and does not expand; the terminal portion of the intestine has in the meantime formed Ect -3pl' Mesam- Fig. 80.
. The development of the chick; an introduction to embryology. Birds -- Embryology. 144 THE DEVELOPMENT OF THE CHICK arises from the neck of the allantois both behind and also at the sides, (cf. Fig. 82.) During the fourth day the distal portion of the allantois pushes out into the portion of the extra-embryonic body-cavity beneath the hind end of the embryo and rapidly expands to form a relatively large sac. But the neck of the allantois remains embedded in the ventral mesentery and does not expand; the terminal portion of the intestine has in the meantime formed Ect -3pl' Mesam- Fig. 80. — Sagittal section through the tail of an embryo of about 35 s. All., Allantois. An. pi., Anal plate, c. C, Central canal of the neural tube. CI., Cloaca. Ectam., Ectoderm of the amnion. Mesam., Mesoderm of the amnion, p'a. G., Post-anal gut. p. i. p., Posterior intestinal portal, s. A., Segmental arteries. Other abbreviations as before. the primordium of the cloaca, from which, therefore, the neck of the allantois appears to arise (Fig. 183); at all stages of incuba- tion the neck of the allantois forms an open connection between the cloaca and the allantoic sac. The Umbilicus. The closure of the body-wall progressively reduces the communication between the embryonic and extra- embryonic body-cavity to a narrow chink between the yolk-stalk. 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 Lillie, Frank Rattray, 1870-1947. New York, Holt
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