Many animals share similar body structures. For instance, your nose, a pig's snout, and an elephant's trunk can all be called noses. Although these noses have different functions and appearances, all have a similar location and structure. Such similar features are called homologous structures. Homologous structures are similar in relative location, structure, or appearance but not necessarily in function.

A structure's shape is often related to its function. A hand used for swimming (a fin) is shaped differently than one used for supporting an animal's weight as it walks. Likewise, a hand used for flying (a wing) is shaped differently than one used to manipulate objects and to use tools.

In this lesson you'll use a program called WebImage to examine X-rays of animal hands in more detail to compare their structures. Based on the morphology, or shape, of the hand, your assignment will be to figure out its function and owner.