Solution: A homologous structure is an example of an organ or bone that appears in different animals, underlying anatomical commonalities demonstrating descent from a common ancestor. The arm of a human and the leg of a dog are homologous structures. They are different and have a different purpose, but they are similar and share common traits. Elephants' tusks are specialized incisors for digging food up and fighting. They are homologous structures to human teeth, inherited from a common ancestor with incisor teeth. The corm of colocasia, tuber of potato, and runner of lawn grass are all homologous structures.