Updated: Mar 8, 2020
Babies are born with around 305 bones. As they grow up, almost a third of these bones fuse together to become single bones, making up the 206-bone adult skeleton.
This is because most of the baby’s unfused bones are located in the skull, which needs to fit through the mother’s birth canal. The infused skull makes the baby’s head flexible enough to fit through the mother’s narrow pelvis.
By the age of two, the baby’s skull bones are fully fused.