That was a severed human forearm. That was a mummified forearm carefully detached from the rest of the body at the elbow in such a way that it wouldn't be difficult to reattach.

Surrounding it on all sides were various jars of specimens. Living, dead, wet, dried, two burned to cinders. There was also a jar of fresh human skin, evidently a biopsy, with one of the sides charred, the faint embers of a crossed out Correspondence symbol seared into that side.

But there still sat the mummified arm, carefully encased in a pocket of velvet. It was so small...