half-pillar

This last remark applies also to the half-pillar against the extreme west wall, which therefore may perhaps be taken as marking the westward limit of the crypt at the time when the vaulting was constructed; while the east wall (excluding the apse) probably marks the contemporary eastward limit -- if, that is to say, the eastern portion of the vaulting has not undergone alteration.

Bell's Cathedrals: The Cathedral Church of Ripon A Short History of the Church and a Description of Its Fabric Cecil Walter Charles Hallett