In humans it's common to see the
remaining pieces of a certain structure that may have been useful to our
ancestors but now it is completely unnecessary. These are called vestigial
structures. The plica semilunaris is shown in this picture is a great
example of a vestigial structure. More commonly known as the 3rd
eyelid, it is a small fold of tissue in the inside corner of our eyes that is a
remainder of the nictitating membrane, which was a transparent eyelid used for
vision while simultaneously moistening the eye.
No comments:
Post a Comment