Observation in order:
1. Chest wall: chest muscles (pectoralis major, pectoralis minor, etc.), chest bones (ribs, sternum, vertebrae, etc.)
2. Mediastinum: anterior mediastinum (thymic tissue, lymphatic tissue, etc.), middle mediastinum (heart, great vessels, tracheobronchus, lymph nodes, etc.), posterior mediastinum (esophagus, descending aorta, etc.);
3. Lung: lung fields, the hilum, interlobular fissures, lobar lung segments, etc;
4. Diaphragm.