Which preposition to use with sternmost

of Occurrences 1%

He looked as gay as a tobacconist's sign when rigged out in his best blue for a lark ashore, where he was occasionally to be seen on horseback with a row of his jovial messmates, all of them sitting with their backs to the horse's head, and the sternmost of them steering the bewildered animal by his tail.

Which preposition to use with  sternmost