The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor.
ðə lˈɪmz ʌv vˈɜːɾɪbɹˌeɪts ɑːɹ kənsˈɪdɚd təbi həmˈɑːləɡəs bɪkˈʌz ðə sˈeɪm ˌʌndɚlˈaɪɪŋ skˈɛlᵻɾəl stɹˈʌktʃɚ wʌz ɪnhˈɛɹɪɾᵻd fɹʌm ðɛɹ lˈæst kˈɑːmən ˈænsɛstɚ.