During the course of evolution some organs remain in the organisms.We have already know about the appendix in the digestive system.In human beings it has no role to play in the process of digestion.
But in Herbivores like rabbit appendix plays an important role
Such type of organs which are not useful in animal are called vestigial organs.
There are nearly 180 vestigial organs in Human beings.
For Example Pinna,Hair on skin,mammary glands in human etc...
That's why Human being is said to be a moving museum of vestigial organs