4.6.1. Many nouns vary in Declension, and they are called Heteroclites.
Note. i.e., "nouns of different inflections" (s, another, , to inflect))
4.6.2. These forms are isolated and archaic, given only in Inanimates, as remains of an older system. They normally consist of one form to mark the Nom.-Acc.-Voc, and another to mark the Oblique cases.
4.6.3. Examples of these forms are:
a. Opposition -Ø / -n: deru /drunos, tree; jus / jusonos, soup
b. Opposition -r / -n: ai. agor, agnos, day. dhemor / dhemnis, thigh
4.6.4. The Heteroclites follow the form of the Genitive Singular when forming the Oblique cases. That is so in the lengthening before declension, vocalism and in the accent, too.