A 3-year-old male who fell from a tree complains of severe pain over the right side of his chest because of a rib fracture at the midaxillary line. He is admitted to the hospital due to his difficulty breathing. Radiographic and physical examinations reveal atelectasis, resulting from the accumulation of blood in his pleural space and resulting hemothorax. What is the most likely the source of bleeding to cause the hemothorax?

Due to rib fracture, the intercostal vessels are damaged, parietal pleura is torn, and blood flows into the pleural space. The loss of negative pressure within the pleural cavity results in collapse of the lung. The carotid vessels would not be affected by the described injury. The pulmonary vessels are found within the parenchyma of the lungs and would not be injured due to an external injury such as that described. The internal thoracic artery is well protected by the sternum and is not the cause of this hemothorax.