This is Ed. He's made of plastic. Apparently, you can buy ones made of real bone but they mostly are sold to universities and they are very, very expensive.
Ed is one of Mac's projects. ("You want to buy a what?") Ed is supposed to be very useful to help Mac prepare for the class he's teaching in the fall on anatomy and kinesiology. It's a little un-nerving to squeeze past Ed in the hallway at night and Bug doesn't like him at all.