 The source of the air forced through the phonic lips is the right nasal passage . While the left nasal passage opens to the blow hole , the right nasal passage has evolved to supply air to the phonic lips . It is thought that the nostrils of the land @-@ based ancestor of the sperm whale migrated through evolution to their current functions , the left nostril becoming the blowhole and the right nostril becoming the phonic lips . 
