Parties who become liable for the same debt of another person, contracting with the same obligee, are co-sureties, and it is not necessary that they become sureties for the debt at the same time, as the other sureties; that is to say, co-sureties need not make their contracts contemporaneously, nor, need they become surety for the same amount, nor is privity of contract an essential, nor is it necessary that they even know that there is another, who is also liable as surety for the same debt.10

Where one of two or more co-sureties pays the debt of the principal debtor, he is entitled to contribution against his co-sureties, that is, he may maintain a suit for the sum, that he has paid in excess of the sum that he himself, as against his co-sureties, would be obliged to pay. Indebitatus assumpsit is the proper action by one co-surety against another, to recover the proportionate share of the common liability due from the co-surety.11 But one who is a surety for another surety is not liable in contribution.12 Other rights of the co-surety as against his co-surety will be spoken of later under a separate head.