Name two homologous structures in vertebrates.Why are they so called?how do such organs help in understanding an evolutionary relationship?

Example of homologous structures in vertebrates - Limbs of birds, mammals, amphibians and reptiles

They are so called since they have similar basic structural plan, but appear different externally and perform different function. However they have evolved from a common ancestor.

Such a homologous characteristic helps to identify an evolutionary relationship between apparently different species.