This is one of my dissertation projects looking at the developmental basis of differences in limb bone length within and between species. I'll update these pages when I have a minute. In the meantime, take a look at these pictures. They represent the growth plates in the humerus, metacarpals and metatarsals of gerbils and mice. See how the growth plates close at different times in the metacarpals and metatarsals? That's part of the question this project is addressing. More soon, I promise...