The Collaborative International Dictionary
Basipterygium
Basipterygium \Ba*sip`te*ryg"i*um\, n. [NL., fr. Gr. ba`sis a base + ptery`gion a fin.] (Anat.) A bar of cartilage at the base of the embryonic fins of some fishes. It develops into the metapterygium. -- Ba*sip`ter*yg"i*al, a.
Wiktionary
basipterygium
n. A cartilage at the base of the fins of some fish that develops into the metapterygium upon maturity