semilunar fold

Infection may cause congestion and erosion of the conjunctivae, conjunctivitis with persistent lacrimation, and semilunar fold swelling in chickens, ostriches, and humans, respectively.

Humans also have vestigial structures, including the ear muscles, the wisdom teeth, the appendix, the tail bone, body hair (including goose bumps), and the semilunar fold in the corner of the eye.

In humans, the plica semilunaris (also known as the semilunar fold) and its associated muscles are homologous to the nictitating membranes seen in some other mammals and other vertebrates.

He picked up on Darwin's concept of "rudimentary" organs such as listed in the "The Descent of Man": the muscles of the ear, wisdom teeth, the appendix, the coccyx (tail bone), body hair, and the semilunar fold in the corner of the eye.