662 embryology: chick 



vena cava, reaches the left or arterial side of the heart and is 

 consequently distributed where it is needed. When the chick 



.a.f. 



s.m. 



W' 



B 



Fig. 517. — Chick embryos in the egg. The embryo, which actually lies with its 

 left side on the yolk sac, has been lifted into a vertical position for the sake 

 of clearness. — After Marshall. 



A , Egg and embryo at the end of the fifth day of incubation ; B, the same at the end of the ninth day. 



a.c, air-chamber ; a.f., false amnion, united with vitelline membrane ; a.f'., the same, further united with 

 allantois ; al., allantois ; a.p., amnion proper ; e., embryo ; tn., site of the sinus terminalis ; s., shell; 

 s.m., shell membrane ; w., white ; reduced to a semi-solid mass ; y.s., yolk sac. 



begins to use its lungs the allantois shrivels up, the foramen 

 ovale closes, and the now wholly venous blood of the inferior 



