Question

Which of the following is not vestigial in man?

• A. Tail vertebrate
• B. Nails
• C. Nictitating membrane
• D. Vermiform appendix

Answer 1

Answer: (B)

Nails

Nictitating membrane or plica semilunaris is vestige of third eyelid and represents a fold in conjunctiva of human eye. Birds and reptiles have well developed third eyelid. The last four coccygeal vertebrae/tail vertebrae are fused together and represent the remnants of long useful tail of human ancestors. Despite being attached to pelvic muscles and ligament, tail vertebrae are non functional because the fused, non moving bones can’t move the muscles. Vermiform appendix is pencil sized cylinder of tissue present as the junction of large and small intestine. In herbivores and leaf eating primates, it served as house of fermenting bacteria that break down cellulose into sugar. Men don’t eat leaves which have made appendix rudimentary non functional structure in them.

Nails, the part of integumentary system, are keratinized hard structures present at dorsal surface of each finger and toe tip. They serve to protect the distal phalanx. The poorly developed/non functional organs of recent forms of organisms, which were fully developed and functional in related ancestral forms are referred to as vestigial organs. This makes option B correct it is fully developed and functional structure while rest three are vestigial.