The Collaborative International Dictionary of English v.0.48:

Osteocomma \Os`te*o*com"ma\, n.; pl. L. Osteocommata, E.
   Osteocommas. [NL. See Osteo-, and Comma.] (Anat.)
   A metamere of the vertebrate skeleton; an osteomere; a
   vertebra. --Owen.
   [1913 Webster]