The thorax is now opened, beginning with the right second costal cartilage. This is cut with the belly of the cartilage-knife about ½-1 cm. from the costal articulation so as to leave as much of the cartilage attached to the sternum as possible. (See Fig. 36.) The cut is made with a rocking motion so that the knife-blade will strike upon the next lower cartilage instead of going through into the thoracic cavity. The cartilages and intercostal muscles are cut in this manner in succession down to the tenth, the cut flaring outward below with the outward curve of the costal articulations. The cartilages forming the lower edge of the ribs are left uncut at this time. When the first opening into the pleural cavity is made attention should always be paid to the possible escape of gas or air (pneumothorax). When pneumothorax is suspected the opening may be made through a little pocket of water formed by holding up the skin-flap and filling the hollow with water. A similar incision is then made through the cartilages on the left side from the second to the tenth. The lower right edge of the ribs is now lifted with the right hand, and the cartilage-knife, held on the flat, with cutting edge toward the abdomen, is put through the opening of the incision through the cartilage and through the diaphragm, and the last cartilages cut by a stroke made outward and slightly upward to avoid injuring the abdominal organs. The last cartilages on the left side are then cut by putting the blade of the cartilage-knife, held on the flat with cutting edge outward, through the diaphragm from the abdominal side, into the incision through the cartilages, and cutting through the lower edge of the ribs in the same manner as on the right. The lower part of the sternum and cartilages is then lifted in the left hand and the diaphragm trimmed off closely beneath it. Still lifting the sternum the tissues of the anterior mediastinum are cut close to its under surface, care being taken not to cut the pericardial sac. The sternum is thus freed up to the cartilage of the first ribs and the sternoclavicular attachments. With the sternum lifted as high as it is possible to do so without breaking it the cartilages of the first ribs are now cut with the blade of the cartilage-knife turned outward to avoid cutting the large vessels and flooding the part with blood from the distended veins. This is possible since the cartilages of the first ribs extend farther outward than those of the second ribs. (See Fig. 36.)