Back cushion

Claim 1

A cushion adapted to engage the small of the back of a human being when in the sitting position comprisiing: a generally planar base portion; a generally arc-shaped small of the back engaging portion merging with said base portion, said arc-shaped back engaging portion having an arc with a substantially constant radius of curvature of from 11 to 17 centimeters within its central section of up to 75 percent of the length of the base portion for lumbar engagement, said back engaging portion having a sacral engaging section between said central portion and said base portion which tapers from said arc of a substantially constant radius toward said base portion at a radius greater than said substantially constant radius, and a dorsal engaging section between said central portion and said base portion, said dorsal engaging section varying from a radius at said central portion which is less than said substantially constant radius to a radius which is greater than said substantially constant radius at the point of merging with said base portion, and wherein said sacral engaging section does not extend to the buttock area during use; and wherein said dorsal engaging section and said sacral engaging section are substantially of equal length and comprise from twelve (12) to twenty (20) percent each of the length of the base portion.