The affixes ṭhañ and ṣṭhan , come after the word śvagaṇa , in the sense of 'he goes by means thereof'.,
This debars ठक् ॥ Thus श्वगणेन चरति = श्वागणिकः 'who lives by dogs'. f. श्वागणिकी ॥ ठन् श्वगणिकः f. श्वगणिका ॥
The form श्वागणिकः is evolved by the breach of rule 7.3.4. Thus श्वगण + ठञ् ॥ Here by 7.2.117, ञ् requires Vriddhi of अ of श्व ॥ But rule 7.3.4 says that instead of Vriddhi, the letter औ comes before व in the case of श्वन् &c. The proper form, therefore, would have been शौवगणिकः ॥ The irregularity is, however, explained by saying that the prohibition contained in 7.3.8 which applies when श्वन् is followed by इञ्, applies also to श्वन् followed by ठञ् ॥ In fact, the rule 7.3.4 does not apply, whenever the word श्वन् is followed by an affix beginning with the letter इ ॥,