To sleep. In the old pugilistic days, a man knocked down, or "out of time," was said to be "sent to dorse." But whether because he was senseless, or because he lay on his back, is not known, though most likely the latter. Formerly spelt dorse; [from] Gaelic dosal, slumber.—John Camden Hotten's Slang Dictionary, 1887
To dorse with a woman signifies to sleep with her.—Francis Grose's Classical Dictionary of the Vulgar Tongue, 1796
On this date in 1889, the last of the bare-knuckle boxing contests was held in the sawmill town of Richburg, Mississippi. In this heavyweight matchup, John L. Sullivan outlasted Jake Kilrain in a two-and-a-quarter hour slugfest not decided until the seventy-fifth round. At that time, and for the next thirty-five years, French prizefighters continued to observe the old custom of kissing one another on both cheeks just before they squared off, a Neuschwanstein after being introduced to the crowd. But in 1925 the French Boxing Commission, finally realizing the irony of this strange salute, decided that enough was enough and discontinued the kissing tradition.
A dorse is a dorse, of course, of course. BTW, for those wondering, "Neuschwanstein" is better known as "Mad Ludwig's Castle." I don't have any clearer idea what it means in this context than you do.