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

Abstract

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.

Structure and biomechanical properties of the trachea of the striped dolphin Stenella coeruleoalba: Evidence for evolutionary adaptations to diving

“…So if it is surprising that the cetacean trachea could remain a dead space, with large quantities of precious air left to no use, a denser and larger vascular network in the submucosa may play a key functional role. Space seclusion may be meaningful in the lower respiratory tract, as in the bronchial tree of dolphins, where several cartilaginous rings even in the smaller ramifications create a structure able to divide the lower airways into tight compartments where air is locked during descent (Engel, 1966;Ito et al, 1967;Yamasaki et al, 1977;Henry et al, 1983;Henk and Haldiman, 1990;Haldiman et al, 1998). But in the middle ear of marine mammals, where a similar situation takes place, vascular sinuses in the mucosa reduce the volume of the dead space when filled, presumably at depth (Welsch and ReidelScheimer, 1997).…”

Discovery of a low frequency sound source in Mysticeti (baleen whales): Anatomical establishment of a vocal fold homolog

“…Although vocal folds (vocal cords, true vocal cords, or true cords) are the prime generator of initial laryngeal sounds in terrestrial mammals, it is currently widely accepted that mysticetes lack them (Carte and MacAlister, 1867;Turner, 1870;Dubois, 1886;Hosokawa, 1950;Purves and Pilleri, 1983;Quayle, 1991;Paterson et al, 1993;Haldiman and Tarpley, 1993). Thus, other regions of the larynx have been suggested as possible sound sources (Beauregard and Boulart, 1882;Benham, 1901;Hosokawa, 1950;Sukhovskaya and Yablokov, 1979;Henry et al, 1983;Reeb and Best, 1999). While the presence of vocal folds has only been recently discovered in odontocetes (Reidenberg and Laitman, 1988), no one has yet confirmed the existence of vocal folds in mysticetes.…”

Anatomy of nasal complex in the southern right whale, Eubalaena australis (Cetacea, Mysticeti)

“…Mysticetes lack the sound-producing nasofacial specializations present in toothed whales (Eschricht & Reinhardt, 1866;Carte & Macalister, 1868;Schulte, 1916;Lawrence & Schevill, 1956;Henry et al 1983;Cave, 1988;Heyning & Mead, 1990). The mysticete nasal passageways are comparatively simple, and appear to conserve the nasal mammalian pattern associated primarily with conducting air for breathing, perhaps with a secondary function of olfaction (Thewissen et al 2011;Godfrey et al 2013).…”