Diaphragm of the diaphragm and it's placement in the chest. Let a represent the spinal column, b the front wall of the chest, Cc the cavity of the chest, and Ca the cavity of the abdomen. At d is represented the diaphragm. As you can see from the figure, as the fibers of the diaphragm are shortened the space in the chest increases which is what takes place during inspiration. On the contrary, during expiration the diaphragm is pushed upward as shown in this figure so the room in the chest is lessened and air is forced out.