1.during the course of evolution,some organs remain in organisms.for example,ependix in digestive system
2.in human beings it has no role to play in process of digestion
3.but in herbivores like rabbit appendix plays an important role
4.such type of organs which are not useful in animal are called vestigial organs
5.there are nearly 18 vestegial organs in human beings
6.for example pinna,hair on skin,mammary glands in man,etc
7.that's why human being is said to be a moving museum of vestigial organs.