0877NOTPerseusAndromeda

0877NOTPerseusAndromeda_Mignard

Perseus, mounted on Pegasus, rescues Andromeda from the sea monster, with Andromeda's family pleading in the foreground

Maybe it's interesting that the cupids are doing all the work at the moment. Perseus receives expressions of gratitude from king and queen, while Andromeda (still mostly chained to the rock) can only express admiration with her eyes. But, the cupids will change all that shortly.

Medusa's head lies silent on the shore, as coral springs from her hair. This reminds one of the detail that Perseus' use of Medusa's head caused a coral reef to grow.

Pegasus, however, is a post-classical inclusion in the story. The winged horse does not technically belong in the Perseus iconography until after the Renaissance. This is a vexing issue: Pegasus was born from the blood of Medusa's decapitation; but classical sources give the winged steed to Bellerophon, not Perseus.

Narrative Gain: Mignard "narrates" the story in the customary (for his time) manner. The "classical" narrative, is different and involves The Pegasus conundrum:
Apollodorus Biblioteca 2.3.2 has Bellerophon riding Pegasus. So does everybody else. BUT at Apollodorus Biblioteca 2.4.2 Pegasus is born from the body of slain Medusa; but Perseus does not ride the horse. Everybody (apparently) agrees. Astronomers, beginning with Aratus (ca. 230 BC) were already putting a horse (sometimes winged, sometimes specifically called "Pegasus") in constellations around Andromeda.