Fig. 2
From: Vocal tract anatomy of king penguins: morphological traits of two-voiced sound production
King penguin trachea and septum trachealis medialis (STM) separating the trachea into two lumina. a: Image of the upper vocal tract of a male king penguin. The right side of the trachea is removed and put aside to expose the medial septum. The STM originates at the bifurcation of the trachea into the two primary bronchi and stretches to the 94th/96th tracheal ring, 6 cm below the larynx. Tracheal rings are numbered 1–125. b/c: 3D reconstructions of trachea, syrinx and bronchi showing different densities of the trachea and STM. Blue indicates ossified tracheal and bronchial rings. Yellow depicts ossified plates within the connective tissue (grey) of the tracheal septum. b: Craniocaudal view into the double lumen trachea showing the STM separating the two tracheal tubes and the irregular ossified plates (yellow) segmentally lined up within the septum. c: Lateral view of the trachea and the ossified plates of the STM