Bronchial tree, lobular division and blood vessels of the nutria (Myocastor coypu) lung--evidence for the individual nature of the bronchioles in the upper and middle lobes.

Four nutria (Myocastor coypu) lungs were examined. The right lung consists of the upper, middle, lower and accessory lobes, whereas the left lung consists of the upper, middle and lower lobes. These lobes are completely separated, and the upper and middle lobes are particularly well developed on either side. Each lung has four bronchiole systems, i.e., dorsal, lateral, ventral and medial. The upper lobe is formed by the first bronchiole of the dorsal bronchiole system. The middle lobe is formed by the first bronchiole of the lateral bronchiole system. The accessory lobe is formed by the first bronchiole of the ventral bronchiole system. The remaining bronchioles of the four bronchiole systems constitute the lower lobe. The right and left pulmonary arteries run across the ventral side of the upper lobe bronchiole and then across the dorsal side of the middle lobe bronchiole. Thereafter the pulmonary arteries run along the dorsolateral side of the bronchi. During their course, pulmonary arteries give off branches running mainly along the lateral or dorsal side of each bronchiole. The pulmonary veins run mainly along the ventral or medial side of the bronchioles, and between them.