They are named in the same order, Rom 16:3; 2Ti 4:19.
Having shorn his head
Referring to Paul, and not to Aquila.
He had a vow
A private vow, such as was often assumed by the Jews in consequence of some mercy received or of some deliverance from danger. Not the Nazarite vow, though similar in its obligations; for, in the case of that vow, the cutting of the hair, which marked the close of the period of obligation, could take place only in Jerusalem.