556 EMBEYOLOGY OF THE LOWEB VEETEBEATES oh. 



ovale) becomes closed so that the blood arriving in the right auricle 

 can only reach the left auricle by the circuitous route through the 



Fig. 246. — Dissections from the right side showing the general arrangement of the viscera of 

 a Fowl embryo at the end of the fifth (A), sixth (B), and eighth (C) days of incubation. 

 (After Duval, 1889.) 



a.s, abdominal air-sac ; all, allantois ; c.a, conus arteriosus ; caec, caecum ; gi, gizzard ; li, liver ; 

 mn, mesonephros ; r.a, right auricle ; r.l, right lung ; V, ventricle ; y.d, yolk-stalk ; y.s, yolk-sac. 



right ventricle and pulmonary circulation, and the allantoic vein, 

 duct of Botallus, and ductus venosus in the liver become obliterated. 



