The na of the verb an 'to breathe', is changed to ṇa , when preceded by an upasarga competent to produce the change, provided it occurs at the end of a pada,
As हे प्राण् ! हे पराण् ! This rule is an exception to 8.4.37 sub, by which final न् in a pada is not changed into ण ॥ The word अन्तः in the sutra is to be understood to be equivalent to पदान्तः, and the rule applies when the word is in the vocative case.
According to some अन्तः is taken to be a part of the last sutra, and has the meaning of 'proximity'. That is the न is changed to ण, if the र is not separated from the न् by more than one letter. Therefore there is no change in परि + अनिति = पर्यनिति ॥ In this view, another अन्त should be taken for the sake of final न्, in हे प्राण् ॥
According to others the form पर्यणिति is valid, and they do not connect अन्तः with the last sutra.
The word प्राण् is a क्विप् formed word, and the न् final is not elided in the Vocative Singular because of the prohibition of 8.2.8; in every other place, when the न् is padanta, it would be dropped; and therefore the illustration is given with Vocative singular, which alone satisfies the requirements of this sutra.,