The diaphragm, which is the principal muscle that act sin breathing. Here you have the cavity of the chest, Cc, laid open, the ribs being cut away in front, and the heart and lungs taken out; DD is the diaphragm. It is fastened to the spinal column behind, to the breast-bone in front, and to the lower ribs all around its side. It is not flat, but arched upward.
GalleriesHuman Lower Respiratory System
Hooker, Worthington First Book in Physiology For the Use of Schools and Families (New York: Sheldon and Company, 1867) 59