Title from item.
"An attack on Philip Thicknesse [alias "Lieutenant Governor Gallstone" and "Dr. Viper"] ... The allusion to 'Sir Sydney's Ape' is obscure. For 'Jocko', Thicknesse's monkey postillion, see BMSat 7721. As a remedy for gall-stone Thicknesse recommended ('inter alia') 'a free use of laudanum, twenty, thirty or forty drops, . . .' 'Memoirs', 1788, i. 161. ... Tim Clayton (personal communication) has identified 'Sir Sydney' as the riding master Sir Sidney Medows, and his 'Ape' as John Crookshanks."--Curator's comments, British Museum online catalog
A monkey-like postillion (i.e. Philip Thicknesse's pet monkey Jocko), rides (right to left) a baboon with a human head which is turned full face. The postillion flourishes his whip above his head with an air of triumph, and holds up in his left hand a bottle labelled 'Laudanum, or the Preservation of Life - prepared by Lieut Genl jackoo, Spanish posttilion to Dr Viper - O Death where is thy Sting?" From each coat-pocket protrudes a bottle labelled 'Extract of Hellebore and Extract of Hemlock'. The scene is the sea-shore with three men-of-war, two being in action; the third flies a British flag. On the right is a low thatched hut in which sit two apes with tails, but wearing mob caps, one weeps, the other holds her by the shoulders as if to comfort her. Cf. British Museum online catalog.