After a word denoting direction, the first vowel of the name of a village or city in the land of the Eastern people, gets the vṛddhi before a taddhita affix having an indicatory ñ , ṇ or k ,
Thus पूर्वैषुकामशमः, अपरैषुकामशमः, पूर्वकार्ष्णमृत्तिकः, अपरकार्ष्णमृत्तिकः 4.2.107. These are village names. पूर्वपाटलिपुत्रकः, अपरपाटलिपुत्रकः, पूर्वकान्यकुब्जः, अपरकान्यकुब्जः ॥
The word प्राचां in this sutra, as well as in 7.3.24, does not here mean 'the eastern grammarians', but 'the eastern countries', because of the context. पूर्वैषुकामशमः is this formed. पूर्वा च असौ इषुकामशमी = पूर्वेषुकामशमी ॥ The compounding takes place by 2.1.50. Then the affix ञ is added to it, in the sense of ततो भवः by 4.2.107. In पूर्वपाटलिपुत्रकः the affix वुञ् is added by 4.2.123. Though Pataliputra is the name of one city, Purva-pataliputra means the Eastern portion of the city Pataliputra.
That place is called 'grama', where people reside, and a 'nagara' is also a 'grama' in this sense. Therefore, the rules which good men observe with regard to 'grama', are observed by them in 'nagara' also. Thus the rule is अभक्ष्यो ग्रामकुक्कुटः, therefore, the नागर cock is also not eaten. So also ग्रामे नाध्ययम् is applied to nagara also. In this grammar also, we see that 'grama' includes 'nagara' also, as in 4.2.109, 4.2.117, 6.2.103. Therefore, where is the necessity of employing the word नगर separately in this aphorism? The two words are separately used, in order to indicate the separate nature and relation of the two kinds of words. The full word पूर्वेषुकामशमी is the name of a 'grama', and not the portion इषुकामशमी ॥ But in पूर्वपाटलिपुत्र, the word पाटलिपुत्र itself is the name of the 'nagara'. In the present sutra, there is the adhikara of अङ्गस्य and of उत्तरपदस्य ॥ We apply these separately to these two classes of words: namely ग्रामवाचिनाम् अङ्गानाम् and नगरवाचिनाम् उत्तरपदानाम् ॥ This we could not have done without employing these words in the sutra. Therefore, in the case of 'grama' word, the vriddhi takes place in that portion of it which follows a direction denoting word (ग्रामवाचिनामङ्गानामवयवस्य दिकशब्दादुत्तरस्य वृद्धिर्भवति). While a nagara word itself gets vriddhi when it is preceded by a direction denoting word (दिशः उत्तरेषां नगराणाम्) ॥ In पूर्वैषुकामशमः, the vriddhi of इषुकामशमी takes place first, and then the combination by sandhi. See on this point 7.3.22.,