A matrice is a mold onto which an impression is embedded of a particular design. These images were used during the papacy of Clement IX for the production of papal medals.
The obverse side is a profile image of Pope Clement IX.
The reverse side is an image of a mother bird feeding her chicks while the words surrounding the image are, allis non sibi clemens, which translates, Merciful to others, not to himself.
Pope Clement IX chose this image and the expression for the matrice attesting to the importance he attributed to this motto.