The pig lung has the dorsal, ventral, medial and lateral bronchiole systems on either side. In addition, a tracheal bronchiole (bronchus) arises from the right side of the trachea. According to the bronchial ramification, the right lung consists of the cranial, middle, caudal and accessory lobes, while the left lung consists of the bilobed middle and caudal lobes. The right and left pulmonary arteries run along the dorsolateral side of the right and left bronchi, respectively. During their coufse, these pulmonary arteries give off arterial branches running mainly along the dorsal or lateral side of each bronchiole. The pulmonary veins run mainly along the medial or ventral side of each bronchiole.