Groined Vault with Zig-Zag Ridge-Joints
A groin vault or groined vault (also sometimes known as a double barrel vault or cross vault) is produced by the intersection at right angles of two barrel vaults. The word groin refers to the edge between the intersecting vaults; cf. ribbed vault. Sometimes the arches of groin vaults are pointed instead of round. In comparison with a barrel vault, a groin vault provides good economies of material and labour. The thrust is concentrated along the groins or arrises (the four diagonal edges formed along the points where the barrel vaults intersect), so the vault need only be abutted at its four corners.
A. D. F. Hamlin College Histories of Art History of Architecture (New York, NY: Longmans, Green, and Co., 1915)
Courtesy the private collection of Roy Winkelman