A finding of a fusion of two approximately spherical primary ossification centers at or near the mid-line through an ossified bony bridge, as indicated by staining.

Two approximately spherical ossification sites attached at or near the mid-line by an ossified bridge. Commonly used for structures arising from two primary centers (e.g., sternebrae, vertebral centra). Applies only to the ossification sites. (Makris S, Solomon HM, Clark R, Shiota K, Barbellion S, Buschmann J, Ema M, Fujiwara M, Grote K, Hazelden KP, Hew KW, Horimoto M, Ooshima Y, Parkinson M, Wise LD. Terminology of developmental abnormalities in common laboratory mammals (Version 2). Part B. Birth Defects Res B Dev Reprod Toxicol. 2009 Aug;86(4):227-327.)