The American Church Dictionary and Cycopedia
The name given to the passageway running around and back of the Altar, being a continuation of the aisles of the church. Generally used for processionals to and from the choir.
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Miller, William James. Entry for 'Ambulatory'. The American Church Dictionary and Cyclopedia. https://www.studylight.org/dictionaries/eng/acd/a/ambulatory.html. 1901.