410. The accentuation of these words is irregular

The accentuation of these words is irregular, as regards both the stems themselves and their inflected forms. Sometimes the one element has the tone and sometimes the other, without any apparent reason for the difference. If the compound is accented on the final syllable, the accent is shifted in RV. to the ending in the weakest cases provided their stem shows the contraction to ī or ū: thus, prā́cā, arvā́cā, adharā́cas, but pratīcā́, anūcás, samīcī́. But AV. and later texts usually keep the accent upon the stem: thus, pratī́cī, samī́cī, antū́cī (RV. has pratī́cīm once). The change of accent to the endings, and even in polysyllabic stems, is against all usual analogy.