Syringeal muscles of a freshly dissected male zebra finch syrinx. (A) Ventral view of the caudal part of the syrinx showing the ventral muscles VS and VTB, and the IBL. The IBL connects the primary bronchi and restricts their lateral movement. Dashed box is shown enlarged in B. (B) Detail of VTB attachment on bronchial half-ring B3. Syringeal muscles are organized in sheets of muscle fibers (arrowheads). (C) Close-up of the rostral attachment sites of the ventral muscles. The VS fibers end on the edge of the tympanum, while the SVTB fibers do not attach onto bone but end in the connective tissue of the CASM. Rostral to the CASM, the extrinsic TL attaches and runs along the trachea up to the larynx. (D) Lateral view of the right hemisyrinx showing the muscle attaching on B3. Some fibers of the STB attach directly on the ML that is located on the inside of B3. (E) Dorsal muscle attachment sites. (F) Lateral view of rostral attachment sites of SVTB and DTB clearly reveals the organization of syringeal muscles in sheets (arrowheads). Individual muscle fibers can be seen within the fiber bundle sheets. The edge of the CASM is indicated by the dashed black line. Abbreviations as listed in Table 1.