A surety is entitled to contribution from a co-surety in respect of their common liability. This particular right is not the result of any contract, but is derived from a equity, on the ground of equality of burden and benefit, and exists whether the sureties be bound jointly, or jointly and severally, and by the same, or different, instruments. There is, however, no right of contribution where each surety is severally bound for a given portion only of the guaranteed debt; nor in the case of a surety for a surety