Day 2: The Heart of the Matter

A 48 Hour Embryo

The chick embryo has almost doubled in length from 33 to 48 hours. The embryo has turned its head and bent it toward the yolk, so that the left side of its head rests on the yolk sac (like a pillow). Eventually the rest of the body will twist to the left so that the embryo is lying on its left side atop the yolk. The eye can now be clearly seen. The heart is now an S-shape and has begun to loop.

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