Meanwhile, a membrane forms around the inside uterine wall, which seals in the egg cell, yolk and albumen. Eventually a mixture of water, salt and calcium surround this membrane and form a thin but structurally sturdy outer shell. This shell is molded in the shape of the uterine wall, thus giving a chicken's egg its distinctive shape. While in the uterus, the egg's narrower end points downward, but it will later turn and be ejected wider end first.

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