. The development of the chick; an introduction to embryology. Birds -- Embryology. FROM TWELVE TO THIRTY-SIX SOMITES 153 infimdibulum (Fig. 83 E); thus the diencephalon may be divided into an anterior and posterior division, parencephalon and synen- cephalon (Kupffer) (Fig. 87). The optic stalks are attached to the floor and ventral zones at the extreme anterior end. The diencephalon includes part of the roof, floor, and dorsal and ven- tral lateral zones of the original neural tube. These may be de- scribed as follows (Figs. 87 and 88): Oes. - Jyy?e/)c Am. Fig. 87. — Optical longitu
. The development of the chick; an introduction to embryology. Birds -- Embryology. FROM TWELVE TO THIRTY-SIX SOMITES 153 infimdibulum (Fig. 83 E); thus the diencephalon may be divided into an anterior and posterior division, parencephalon and synen- cephalon (Kupffer) (Fig. 87). The optic stalks are attached to the floor and ventral zones at the extreme anterior end. The diencephalon includes part of the roof, floor, and dorsal and ven- tral lateral zones of the original neural tube. These may be de- scribed as follows (Figs. 87 and 88): Oes. - Jyy?e/)c Am. Fig. 87. — Optical longitudinal section of the head of an embryo of 30 s. The heart is represented entire. Atr., Atrium (auricles). B. a., Bulbus arteriosus. D. v., Ductus venosus. Lg., Laryngo-tracheal groove. Oes., Oesophagus, or. pi., Oral plate, which has begun to rupture. Parenc, Parencephalon. Ph., Pharynx. Stom., Stomach. Synenc, Synencephalon. Th., Thyroid. S. v., Sinus venosus. Ven. R., Right ventricle. Other abbreviations as before. The roof rises quite sharply from the velum transversum, and is indented between the parencephalic and synencephalic divi- sions as already noticed. It is relatively thin. About the 30- 35 s stage the epiphysis (pineal body) begins to form as an evagination from about the middle, and by the 36 s stage is a small hemispherical protuberance (Figs. 86 and 88). The floor becomes extremely thin in the center of the recessus opticus, which marks its anterior end; immediately behind this is a sudden and. 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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