Comparative Anatomy of the Lower Respiratory Tract of the Gray Short-tailed Opossum (Monodelphis domestica) and North American Opossum (Didelphis virginiana)

The present study describes the lower respiratory tract anatomy of the gray short-tailed opossum (Monodelphis domestica) and North American opossum (Didelphis virginiana). The trachea of the gray short-tailed opossum consists of 25 c-shaped tracheal cartilages. The trachea of the North American opossum consists of 28 c-shaped cartilages. The right lung of both species is separated into cranial, middle, caudal and accessory lobes by interlobar fissures. The left lung consists of unseparated cranial and caudal lobes. The right and left pulmonary arteries of the gray short-tailed and North American opossums divide into pulmonary lobar arteries. The pulmonary lobar veins join to form pulmonary veins. In the gray short-tailed opossum, the pulmonary lobar veins join to form a right and left pulmonary vein which join to form a common pulmonary venous trunk. In the North American opossum, a similar pattern occurs however the common pulmonary venous trunk is formed from three pulmonary veins (right, left and middle). Vascularization of the lung parenchyma is via the bronchial artery, a branch of the bronchoesophageal artery. Right and left bronchial branches course along the dorsal surface of the principal bronchi toward the hilus of the lung. In both species, the left bronchial branch anastomoses with a mediastinal artery originating from the aorta. Cranial deep cervical, cranial mediastinal and tracheobronchial lymph nodes drain the lower respiratory tract of both species. Sympathetic innervation to the lungs of the opossums comes from the sympathetic trunks as thoracic splanchnic nerves. Parasympathetic innervation to the lungs is via branches from the vagus nerves.

The trachea and principal bronchi of the gray short-tailed opossum are lined by pseudostratified ciliated columnar epithelium. Bronchial cartilages are irregular, shaped plates and localized to the extrpulmonary portion of the principal bronchus. The secondary and tertiary bronchi and primary and secondary bronchioles are lined by simple ciliated columnar epithelium. The terminal bronchioles and proximal portion of the respiratory bronchioles are lined by simple ciliated cuboidal epithelium. The distal portion of the respiratory bronchioles and the alveolar ducts are lined by simple squamous epithelium. The alveoli are lined by type I and II pneumocytes.