छन्दस्यृदवग्रहात्

In the छन्दस् , न of a second term is changed into ण , when prior term ends with a short ऋ even when there is an अवग्रह or hiatus between the two terms.
In the Veda, न् becomes ण्, after a ऋ, after which in Padapatha, the word appertaining to it is divided. Thus in Pada-patha the words नृमणाः &c, are separated, and are read as नृ, मणाः ॥ The word अवगृह्यते = विच्छिद्य पठ्यते, as in Pada-patha. ऋदवग्रहात् means 'after a short ऋ which is an avagraha'. The ऋ here, of course, means 'a word ending in ऋ', because ऋ alone cannot be a purvapada. The णत्व only took place during sanhita, and in Pada reading this ण would not have remained, hence this sutra.

Why have we used the word avagraha in the sutra? Because we have already said that the word sanhita governs all sutras of this chapter. So the न is changed to ण in the Sanhita state in these; and the ण is retained, when in the state of avagraha. The word avagraha in the sutra indicates the scope of the rule. The न is changed to ण after that ऋ only, which is capable of avagraha, namely that ऋ which stands at the end of a word (pada), and not that which is in the body of a word. Thus in नृमणाः, पितृयाणम्, the ऋ is capable of avagraha, as it is at the end of a word नृ or पितृ; but when it is not at the end of a word, it can never become avagraha, and will not produce the ण change.

The word पूर्वपदात् is understood here. The word अवग्रह means a hiatus or separation. Thus पितृ याणम्, नृ मणाः ॥ Here ऋ is अवगृह्य ॥ The change of न into ण is effected ordinarily then, when the terms, one containing the cause, and the other न, are in संहिता or conjunction. For the rules of Sandhi and the rules like these can apply only to words in sanhita. The present rule is an exception to it, and here, even when the words are not in संहिता, but there is an actual hiatus between the two, the change still takes place. The word संहिता of 8.2.108, exerts regulating influence upto the end of the Book.