चतुष्पाद्भ्यो ढञ्

Operational rule vidhi

The affix ढञ् comes in the sense of a descendant after the bases denoting quadrupeds.

Word by word (padaccheda)

Left context चतुष्पाद्भ्यः pañcamī · bahuvacanaSubstitute / term prathamā · ekavacana

Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

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Pink letters are it-markers (anubandhas), tags dropped by 1.3.9. Hover or tap one for the rule that marks it, or try the it-letter finder.

Full reading

चतुष्पाद्भ्यः ढञ्

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

The affix ढञ् comes in the sense of a descendant after the bases denoting quadrupeds.
This debars अण् &c. Thus कमण्डलु + ढञ् = कामण्डलेयः 4.4.147, the उ being elided before ढ)). So also शौन्तिबाहेयः and जाम्बेयः from शुन्तिबाहु and जम्बु॥

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.