Birds
In birds, the process of breaking open the eggshell is commonly referred to as pipping.
Chicks have a pipping muscle on the back of their necks. It is this muscle which gives them the strength to force the egg tooth through the inner membrane of the eggshell.
When a chick becomes too large to absorb oxygen through the pores of its eggshell, it uses its egg tooth to peck a hole in the air sac located at the flat end of the egg. This sac provides a few hours worth of air, during which the chick breaks through the eggshell to the outside. The egg tooth falls off several days after hatching.
Kiwis lack an egg tooth, instead using their legs and beak to break through a relatively thin eggshell. The superprecocial megapodes possess an egg tooth in their early embryonic development, but instead use their claws during hatching.
Read more about this topic: Egg Tooth
Famous quotes containing the word birds:
“The kiss of the sun for pardon,
The song of the birds for mirth,—
One is nearer God’s heart in a garden
Than anywhere else on earth.”
—Dorothy Frances Gurney (1858–1932)
“It was soldiers went marching over the rocks
And still the birds came, came in watery flocks,
Because it was spring and the birds had to come.
No doubt that soldiers had to be marching
And that drums had to be rolling, rolling, rolling.”
—Wallace Stevens (1879–1955)
“Alas, so all things now do hold their peace:
Heaven and earth disturbed in no thing:
The beasts, the air, the birds their song do cease;
The nightes chare the stars about doth bring.”
—Henry Howard, Earl Of Surrey (1517?–1547)