In ichthyology, the pterygoid, a small bone connecting the palatine with the quadrate.(noun)
The Century Dictionary (Public Domain)
Use "externum" in a sentence
"In discussions we normaly only speak about the forum externum and not the forum internum so if we speak of "somebody committed a sin" it is to be presumed that we only want to speak about the objective level, so materialiter speaking, because it is not ours to judge the forum internum."
"So this usage seems to be ok - otherwise you were not at all allowed to utter the sentence "sb. comitted a sin" in such discussions about the forum externum."
"Much changed when the locus of penance shifted and the forum externum was replaced by the forum internum, i.e., when the treatment of sinners became more private and less formal."