Our Two Skeletons

by Catherine Kettrick

It may seem odd to think of having two skeletons–don’t we just have one?

Well, yes, but developmentally one happened before the other.

The first skeleton we develop is our axial skeleton.  The axial skeleton is the head, spine and ribs. All vertebrates have an axial skeleton.  Most vertebrates also have an appendicular skeleton–legs and arms (people), legs and legs (horses), legs and wings (birds).  Snakes only have an axial skeleton, and fish–well, their appendicular skeleton isn’t much to speak of.

Why is this distinction important?  When you are thinking about how you move, and want to move more easily, that natural coordination starts with your axial skeleton–your head moves, and your body (your spine and rib cage) follow.  However, as soon as your axial skeleton starts moving, your appendicular skeleton starts moving too–your arms and legs become part of that overall coordination.

This picture shows the axial skeleton in black; everything else is appendicular.  Pay particular attention to what are arms and legs–more than you may think!