Source : Webster's Revised Unabridged Dictionary (1913)

Mesopterygium \Me*sop`te*ryg"i*um\, n. [NL., fr. Gr. me`sos
   middle + ? a fin.] (Anat.)
   The middle one of the three principal basal cartilages in the
   fins of fishes. -- {Me*sop`ter*yg"i*al}, a.