Why is it that we are born with 300 bones, but by adulthood we only have 206 in our bodies?

ive never heard of this, i never heard of it in my anatomy class. but when babies are born, they have many bones, but alot of the bones are stil cartilage. but what he said about the skull, theres actually either 4 or 5 bones that make it up.

when i was a baby i had a skull problem and my plates werent shifting right :O they got better though and now im all yay!

bones start off mostly made up of cartilage, with areas called ossification centres or growth plates. As the cartilage turns to bone (ossifies), these growth plates fuse, so you end up with less bones. This is particularly apparent in places like the pelvis, which is made up of three different bones (the iliam, ischium and pubic bones) but which fuse during growth.