Gross anatomy of the respiratory system of the bowhead whale, Balaena mysticetus.

Components of the respiratory system from seven bowhead whales have been examined. The paired and laterally curved external nares are passively closed by a valve-like mass located in the rostral, lateral, and ventral walls of the nasal vestibules. Nasal septal cartilages are paired smooth plates rostrally changing to accordion-like folds caudally. The epiglottic and arytenoidal protuberances of the larynx are typically cetacean, but blunt. The cricoid cartilage is not a complete ring, but an elongated, inverted, trough-shaped structure. The thyroid cartilage is trough-shaped with elongated cranial cornua curving dorsocaudally from each thyroid lamina. A conical mass of skeletal muscle serves as the floor of the short trachea and also surrounds the termination of the laryngeal sac. The trachea is dorsoventrally compressed, lacks a tracheal bronchus, and its width equals its length. The principal bronchi give rise to lobar bronchi at obtuse angles. Large segmental bronchi branch extensively from lobar bronchi near the mediastinal lung surface. The lungs are rectangular and of nearly uniform thickness throughout, without external or internal lobulation.