This picture shows the development inside a bird egg:

enter image description here

This shows the connection of the embryo to the yolk sac. Does this mean birds have navels? And if so, what happens to the umbilical cord once the bird hatches?


1 Answer 1


All animals develop in this way, whether they are oviparous (developing in an egg) or viviparous (developing inside their mother, or live-birth).

From Wild Birds Unlimited:

All mammals have navels or belly buttons where the umbilical cord distributes nutrients between a mother and her fetus. After birth, the umbilical cord is cut and a scar develops on the abdomen where the hole closes.

Of course avians or birds hatch from eggs which are virtually self-contained life-support systems that only require warmth and oxygen to develop properly. Instead of an umbilical cord scar, birds have yolk sac scars at hatching. This is where the chick embryo is attached to the yolk sac. But don’t look for any bird belly button rings. The scars usually heal and become virtually invisible.

enter image description here

As for their umbilical cord, it looks like it falls off when the chick hatches if it is not fully absorbed along with the yolk sac, along with everything else contained in the egg (although there is not a lot of material left within the egg by the time the chick is ready to hatch).

Inside a bird's egg there is a tiny cord that connects the developing embryo to the yolk sac. When the egg cracks open, the hatchling does in fact have a miniscule residual scar where the cord was.

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    $\begingroup$ I doubt it falls off, the sources I looked up say that the whole yolk sac goes inside the bird's body. $\endgroup$
    – Anixx
    May 1, 2014 at 14:07
  • $\begingroup$ You are right about the yolk sac! msucares.com/poultry/reproductions/poultry_chicks_embryo.html - However, it says that when they are born some residual umbilical cord tissue is still attached to the chick. justcockatiels.net/assist-hatches.html There are sometimes problems with the yolk sac being absorbed as well, so this could be related. $\endgroup$
    – Bunk
    May 1, 2014 at 14:26
  • $\begingroup$ The first sentence is a fragment and doesn't make any sense. If you remove the parenthetical expressions, it reads: "All animals that develop in this way, whether they are oviparous or viviparous." Did you mean to say more? $\endgroup$
    – JYelton
    Aug 11, 2014 at 18:08
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    $\begingroup$ How obnoxious of me. 'That' was removed. $\endgroup$
    – Bunk
    Aug 14, 2014 at 20:09

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