Hæres suns

In the civil law. A man's own heir; a decedent's proper or natural heir. This name was given to the lineal descendants of the deceased.

Inst. 3, 1, 4 —5. —.

Haeredes sui et necessarii. In Roman law. Own and necessary heirs; i. the lineal descendauts of the estate-leaver. They were called "necessary" heirs, because it was the law that made them heirs, and not the choice of either the decedent or themselves. But since this was also true of slaves (when named "heirs" in the will) the former class were designated "sui et necessarii," by way of distinction, the word "sui" denoting that the necessity arose from their relationship to the decedent.

Mackeld. Rom. Law, § 733.