FIGURE 3.

Anatomy of the songbird syrinx and phonatory mechanism. (A) Ventrolateral external view of a thrasher syrinx depicting syringeal muscles. (B) Cartilage components of the syrinx include three tracheo-bronchial semi-rings (A1–A3) as well as the tympanum (Ty), which contains at its caudal end the pessulus (P), an important attachment site for the medial labium (ML). (C) Schematic ventral view of the songbird syrinx in quiet respiratory (left panel) and phonatory (center and right panels) configurations. During vocalization, the medial (ML) and lateral labia (LL) are set into vibration when they are adducted into the expiratory air stream. In preparation for phonation, the syrinx moves rostral. Contraction of the ipsilateral dorsal syringeal muscles (dS and dTB) rotates the bronchial cartilages into the syringeal lumen, moving the lateral and medial labia into the expiratory air stream where they are set into vibration to produce sound. Phonation may be bilateral (not shown) or unilateral. Unilateral phonation is achieved by closing one side of the syrinx through full adduction of the labium on that side, so that sound (wavy arrows) is only generated on the partially open contralateral right (centre panel) or left (right panel) side. Abbreviations: B, bronchus; ICM, membrane of the interclavicular air sac; T, trachea; M, syringeal muscle; ML, medial labium; LL, lateral labium; MTM, medial tympaniform membrane; P, pessulus; TL, m. tracheolateralis; ST, m. sternotrachealis; vS, m. syringealis ventralis; vTB, m. tracheobronchialis ventralis; dTB, m. tracheobronchialis dorsalis; dS, m. syringealis dorsalis; T, tracheal cartilage; Ty, A1–A3, B, bronchial cartilages; P, pessulus.

(A) and (B) Modified from Riede and Goller (2010). Figure legend is modified from Suthers et al. (1999).