isabelcostasixties:

Space Age Fashion, London 1969
Girls are pictured modeling the usheretts dress of the future designed especially for them by Uniformula of London, a company who make and design uniforms for the Hotel and Cinema trade. October 1969

They were anticipating that in the future usherettes would be required to have popcorn and drinks dispensers surgically implanted in their bellies so would need quick and easy access to them.