lay on belly (be descriptive)
forehead to floor
arms at sides
legs straighten and spread
crawl to Free Person on belly
(by command of Master; or demonstrate submission or communicate a need)
Kajira of Gor, page 427 and Mercenaries of Gor, page 19

This position is used for a variety of reasons, sometimes as punishment.

A crawling position... then in this position she crawls or slithers to the Master.

Book 19, page 427
"Stop," he said. "To your belly." Then I was on my belly, on the tiles, my hands at the sides of my head, prone, before his curule chair.