seated with one's legs astride another's shoulders ...1754 Sc.
of unknown origin
FIRST DOCUMENTED USE
1754 - see EXAMPLE below
"...my side happen'd to be newmost, an' the great hudderen carlen was riding hockerty cockerty upo' my shoulders in a hand-clap: for the wile limmer was fae dozn'd an' funied wi' cauld...
From: Ajax; His Speech to the Grecian Knabbs from Ovid's Metam. Lib. XIII
- Robert Forbes
A Journal from London to Portsmouth