Adam Hartstone-Rose studies the muscles of forearms, which are surprisingly intricate and easily overlooked. The delicate movements of our hands, for example—like the ability to play a Mozart piano concerto—are only possible thanks to these sinews.

But Hartstone-Rose doesn’t study only human forearms: he specializes in those of many primates, and comparing anatomical differences between species. When his lab at North Carolina State University happened across a dead aye-aye specimen, he was thrilled. “They have these famously strange hands and bizarre fingers,” he says—all the better for research.

The aye-aye (Daubentonia madagascariensis), if you’re unfamiliar, is one of nature’s more absurd creations. These house cat-size lemurs, native to Madagascar, have super-long, spindly third and fourth fingers that they