Ossified structural elements of the male and female zebra finch syrinx. (A) Ventral and (C) dorsal view of male syringeal skeleton surface rendering based on μCT datasets with 5 μm isotropic voxel resolution. (B) Ventral and (D) dorsal view of the female syringeal skeleton. Muscle attachment sites leave impressions on the surface of the tympanum (black arrowheads in A) and on bronchial half-rings B1 and B2 (insets). Abbreviations as listed in Table 1.