Exotic species of monkeys from the private zoo of Herzog Christian Ludwig von Mecklenburg-Schwerin. The monkeys depicted in the painting are the common marmosets (Callithrix jacchus).
Hackert, Jacob Philipp; Two Views of a Dead Boar with a Mastiff and Two Other Dogs; National Trust, Attingham Park; http://www.artuk.org/artworks/two-views-of-a-dead-boar-with-a-mastiff-and-two-other-dogs-131001