If you're ever lucky enough to witness a chick hatching, you'll notice that the umbilical cord is attached to the navel. Once the chick breaks through the eggshell, the egg tooth at the end of its beak cuts the umbilical cord and the chick is free!
The umbilical cord is an essential part of a chick's development. It's attached to the yolk sac, which provides the chick with nutrients and oxygen while it's growing inside the egg. Once the chick hatches, the umbilical cord is no longer needed and will eventually fall off.