An affix -- prāgdīvyato'ṇ [[4.1.83]] etc. comes after a word in the Accusative -2nd case in construction in the sense of 'what goes thereto', provided that, which goes, is a road or a messenger.,
Thus स्रुघ्नम्गच्छति = स्रौघ्नः \a road or a messenger that goes to Srughna.\ So also माथुरः ॥ The road may either lead to Srughna, or being in Srughna, be used for going.
Why do we say पथिदूतयोः \meaning a road or a messenger\. Observe स्रुघ्नं गच्छति सार्थः 'he goes to Srughna for his own sake'.,