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Codman's triangle

[kŏd′mənz]
n.
  1. The interface between a growing bone tumor and normal bone, appearing in an x-ray as an incomplete triangle formed by the periosteum.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.