MadSci Network: Development Query:

Hi Becky, That is a very interesting question and at first it doesn't seem to make sense that the answer could be yes. But the answer is yes, children have more bones than adults. Why is that? If you have a baby brother or sister, or if you have friends who have baby brothers or sisters (about 1 or 2 years old)you may have been told not to push on the "soft spot" on the baby's head. If you try to find that "soft spot" on your head or your friends' heads, it is not there. You see, as babies get older, that "soft spot" disappears. There is no magic about it, what happens is that as bones of the skull develop they start out as several bony segments and eventually fuse into a single bone. So, while the top of the skull in the adult is composed of 4 bones, in a new born there may be as many as 8 separate bone segments (depending on the age of the baby and the manner in which those bones develop). Another way that kids have more bones than adults is due to a cartilage known as the "epiphyseal plate." This is also known as the "growth plate" and every long bone, such as the humerus (the bone of the arm) has an epiphyseal plate at each end. The rounded parts of the long bone than are separated from the long part (shaft or diaphysis) of the long bone. So in an adult the humerus is a single bone, composed of a shaft (diaphysis) and two heads (epiphyses), all fused into a single bone. However, in a growing child the humerus is composed of three distinct, separate bones, the diaphysis and the two epiphyses. So the adult has a right and a left humerus (= 2 bones) whereas the child has two epiphyses and a diaphysis on the right side and two epiphyses and a diaphysis on the left side (=6 bones). But when the child stops growing, the epiphyses will fuse with the diaphysis and then that child will also have 2 bones rather than six. I hope you don't mind that the answer is so long, but it is the story of a long bone, isn't it? Good luck in school. Leslie Gartner Anatomy, OCBS Dental School University of Maryland Baltimore, MD

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