. The development of the chick; an introduction to embryology. Birds -- Embryology. 212 THE DEVELOPMENT OF THE CHICK form from three days sixteen hours to ten days. In Fig. 121 A (three days sixteen hours) the form of the head is defined by the brain, eyes, and visceral arches. The cervical flexure is strongly marked. There is no neck. The heart makes a large protuberance immediately behind the head. The limb-buds are rounded swellings. In Fig. 121 B (five days one hour) the cer- vical flexure is less marked; the enlargement of the mid-brain. Fig. 122. — Embryo of 7 days' and 7 hours' incubati
. The development of the chick; an introduction to embryology. Birds -- Embryology. 212 THE DEVELOPMENT OF THE CHICK form from three days sixteen hours to ten days. In Fig. 121 A (three days sixteen hours) the form of the head is defined by the brain, eyes, and visceral arches. The cervical flexure is strongly marked. There is no neck. The heart makes a large protuberance immediately behind the head. The limb-buds are rounded swellings. In Fig. 121 B (five days one hour) the cer- vical flexure is less marked; the enlargement of the mid-brain. Fig. 122. — Embryo of 7 days' and 7 hours' incubation x 5. (After Keibel and Abra- ham.) makes a more pronounced protuberance of the head in this region; the heart has retreated farther back into the thorax, and the neck is. thus indicated. The main divisions of the limbs are beginning to appear. In Fig. 122 (seven days seven hours) there are marked changes: The cervical flexure is practically lost. The elevation of the head and retreat of the heart into the thorax have produced a well-marked neck. The upper. 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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