The Collaborative International Dictionary
Opisthion
Opisthion \O*pis"thi*on\, n. [NL., fr. Gr. ? hinder.] (Anat.) The middle of the posterior, or dorsal, margin of the great foramen of the skull.
Wiktionary
opisthion
n. (context anatomy English) The middle of the posterior, or dorsal, margin of the great foramen of the skull.