Henry's pocket - a.k.a. the Cutaneous Marginal Pouch - is a fold of skin found on the outer ear (pinnae) of many mammals. Weasels, bats and some cats and dogs have prominent versions of it. And there are vestigial traces in the human ear.

Its function is unknown, though it's presumed that it might have some influence on high-frequency sound that's reflected into the ear canal.

See : Cole, LK. Anatomy and physiology of the canine ear. Veterinary Dermatology , 20: 412-21.