After an ordinal numeral up to 11 exclusive, comes the affix an , the word retaining its denotation when a 'part' is meant, but not so in the chandas (Vedas).,
This is for accent also. Thus च꣡तुर्थः, प꣡ञ्चमः, स꣡प्तमः, न꣡वमः, द꣡शमः ॥ Why do we say प्रागेकादशः 'before eleven'? Observe एकादशः꣡, द्वादशः꣡ no change of accent 6.1.223. Why do we say 'not in the Chhandas'? Observe, पञ्चममिन्द्रियस्यापाक्रामत (पञ्चम꣡ has acute on the final being formed by डट् preceded by मट् 5.2.48, 5.2.49.,