9 The very same thing also He has done with regard to the heart. For inasmuch as the heart has preeminence over all the members in our body, and that the supreme power over our whole life is entrusted to it, and death happens when it receives but a slight blow; He has fenced it about on every side with stiff and hard bones, surrounding it by the protection of the breast-bone before, and the blade-bones behind. And what He did with respect to the membranes of the brain, He has done in this instance also. For in order that it might not be rubbed and pained in striking against the hard bones which encompass it, in the throbbing and quick pulsation to which it is subject in anger and similar affections, He both interposed many membranes there, and placed the lungs by the side of it to act the part of a soft bed to these pulsations, so that the heart may break its force on these without sustaining injury or distress.
But why do I speak of the heart, and of the brain, when if any one will investigate even the very nails, he will see the manifold wisdom of God displayed in these; as well by their form, as by their substance and position. I might also have mentioned why our fingers are not all equal, and many other particulars besides; but to those who are inclined to attend, the wisdom of God Who created us, will be sufficiently clear from what has been said. Wherefore, leaving this department to be investigated with diligence by those who are desirous of the task, I shall turn myself to another objection.
Source: Homilies on the Statues (New Advent)