. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. 176 THE DEVELOPMENT OF THE CHICK an intermediate free portion. At about the 26 s stage an opening (cleft) forms at the dorsal adhesion, but none at the ventral; thus the first visceral cleft is confined to the dorsalmost portion of the pouch (Fig. 100). This opening closes about the end of the fourth day; the ventral portion of the pouch then flattens out, and the dorsal portion expands upwards towards the otocyst (Fig. 102). The first visceral (mandibular) arch thickens greatly between the 14 and
. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. 176 THE DEVELOPMENT OF THE CHICK an intermediate free portion. At about the 26 s stage an opening (cleft) forms at the dorsal adhesion, but none at the ventral; thus the first visceral cleft is confined to the dorsalmost portion of the pouch (Fig. 100). This opening closes about the end of the fourth day; the ventral portion of the pouch then flattens out, and the dorsal portion expands upwards towards the otocyst (Fig. 102). The first visceral (mandibular) arch thickens greatly between the 14 and 35 s stages, the ventral ends project a little behind the oral invagination, and subsequently meet to form the primor- dium of the lower jaw (Figs. 125 and 126, Chap. VII). A pro- %=^4^- ^f. KS. d?<?.^. i//r^ tvfJ. Fig. 101. — Frontal section through the pharynx of a 35 s embryo. a. a. 1, 2, 3, 4, First, second, third, and fourth aortic arches. Hyp., An- terior lobe of the Hypophysis. J., Jugular vein, Oral cavity, p. br., Post- branchial portion of pharynx. Ph., Pharynx. Th., Thyroid, v. A. 1, 2, 3, First, second, and third visceral arches, v. C. 1, First visceral cleft, v. F. 2, 3, Second and third visceral furrows, v. P. 2, 3, 4, Second, third, and fourth visceral pouches. Ill, Third cranial nerve. jection of the upper anterior border just behind the eye is the beginning of the maxillary process, or primordium of the maxillary portion of the upper jaw. The second visceral pouch likewise becomes adherent to the ectoderm of the second visceral furrow at its dorsal and ventral ends, and openings are formed in each adhesion by the 35 s stage (Fig. 100); the dorsal opening is small and oval (later becoming more elongated) while the ventral one is a long, narrow fissure; they are separated only ])y a narrow bridge of tissue, and close during the fourth day. The third visceral pouch behaves like the second, forming a. Please note that these images are extracted from scann
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Keywords: ., bookauthorlilliefrankrat, bookcentury1900, booksubjectembryology
