The internal and external elastic laminae were clear in the pulmonary artery. The smooth muscle, elastic fibers and collagen fibers in the pulmonary artery were positively correlated with its outer diameter. 牦牛肺内肺动脉内、外弹性膜清晰可辩,肺内肺动脉管壁内平滑肌、弹性纤维、胶原纤维的含量与管径成正比。