26. So too one might suppose of the heart, that it is itself like some safe house fitted with the most solid defences, fortified by the enclosing walls of the bones round about; for in rear there is the spine, strengthened on either side by the shoulder-blades, and on each flank the enfolding position of the ribs makes that which is in the midst between them difficult to injure; while in front the breast-bone and the juncture of the collar-bone serve as a defence, that its safety may be guarded at all points from external causes of danger.