His own self, not him own self.
Their own selves, not them own selves.
[§ 519]. The construction of self and a personal pronoun with a verb may be noticed in this place. It is only in the case of the two pronouns of the singular number that any doubt can arise.
1. When myself or thyself stands alone, the verb that follows is in the third person—myself is (not am) weak, thyself is (not art) weak. Here the construction is just the same as in the proposition my body is weak.
2. When myself or thyself is preceded by I or thou, the verb that follows is in the first person—I, myself, am (not is) weak; thou, thyself, art (not is) weak.
CHAPTER VIII.
ON THE POSSESSIVE PRONOUNS.
[§ 520]. The possessive pronouns fall into two classes. The first class contains the forms connected, partially in their etymology and wholly in their syntax, with my and thy, &c. The second class contains the forms connected, partially in their etymology and wholly in their syntax, with mine and thine, &c.