c. The same change appears when the law as to finals causes the loss of the aspiration at the end of the root: see above, 141.
d. But from dah, duh, druh, and guh are found in the Veda also forms without the restored initial aspirate: thus, dakṣat; adukṣat; dudukṣa etc.; jugukṣa; mitradrúk.
e. The same analogy is followed by dadh, the abbreviated substitute of the present-stem dadhā, from √dhā (667), in some of the forms of conjugation: thus, dhatthas from dadh + thas, adhatta from adadh + ta, adhaddhvam from adadh + dhvam, etc.
f. No case is met with of the throwing back of an aspiration upon combination with the 2d sing. impv. act. ending dhi: thus, dugdhi, daddhi (RV.), but dhugdhvam, dhaddhvam.
Surd and Sonant Assimilation.
156. Under this head, there is especially one very marked and important difference between the internal combinations of a root or stem with suffixes and endings, and the external combinations of stem with stem in composition and of word with word in sentence-making: namely —
157. a. In internal combination, the initial vowel or semivowel or nasal of an ending of inflection or derivation exercises no altering influence upon a final consonant of the root or stem to which it is added.
b. To this rule there are some exceptions: thus, some of the derivatives noted at 111 d; final d of a root before the participial suffix na (957 d); and the forms noted below, 161 b.
c. In external combination, on the other hand, an initial sonant of whatever class, even a vowel or semivowel or nasal, requires the conversion of a final surd to sonant.
d. It has been pointed out above (152) that in the rules of external combination only admitted finals, along with s and r, need to be taken account of, all others being regarded as reduced to these before combining with initials.
158. Final vowels, nasals, and ल् l are nowhere liable to change in the processes of surd and sonant assimilation.
a. The r, however, has a corresponding surd in s, to which it is sometimes changed in external combination, under circumstances that favor a surd utterance (178).
