implied authority

where a party to a negotiable instrument intrusts it to the custody of another with blanks not filled up, whether it be for the purpose to accommodate the person to whom it was intrusted, or to be used for his own benefit, such negotiable instrument carries on its face an implied authority to fill up the blanks and perfect the instrument; and as between such party and innocent third parties, the person to whom it was so intrusted must be deemed the agent of the party who committed such instrument to his custody—or, in other words, it is the act of the principal, and he is bound by it.