. The development of the chick; an introduction to embryology. Birds -- Embryology. 360 THE DEVELOPMENT OF THE CHICK have entirely disappeared. Tiie surviving arches are the third or carotid arch, the fourth or aortic arch, and the sixth or pul- monary arch. Up to this time the development is symmetrical on both sides of the body. During the fifth and sixth days the two sides become asymmetrical, the fourth arch becoming reduced on the left side of the body and enlarged on the right. Fig. 207 shows the condition on the tw^o sides Fig. 206.—Camera sketch of the aortic of the body on the sixth d
. The development of the chick; an introduction to embryology. Birds -- Embryology. 360 THE DEVELOPMENT OF THE CHICK have entirely disappeared. Tiie surviving arches are the third or carotid arch, the fourth or aortic arch, and the sixth or pul- monary arch. Up to this time the development is symmetrical on both sides of the body. During the fifth and sixth days the two sides become asymmetrical, the fourth arch becoming reduced on the left side of the body and enlarged on the right. Fig. 207 shows the condition on the tw^o sides Fig. 206.—Camera sketch of the aortic of the body on the sixth day. arches of the left side of a chick em- Jf ^hg fourth arch of the two bryo 4i days old. From an injected g-^j^^ ^^ compared it will be specimen. (After Locy.) ^^^^ ^^^^ ^^^ ^^^^ ^^^ ^^ ^^_ Abbreviations as m 1* ig. 20o. duced to a very narrow rudi- ment which has lost its connection with the bulbus arteriosus, while on the right side it is well developed. Another important change illustrated in the same figure is the reduction of the dorsal aorta between the upper ends of the carotid and aortic arches to a narrow connection. Two factors co-operate in the diminution. 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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