Functional-morphological Diversity and Complexity of the Larynx as a Basis for Vocal Complexity in Birds: Analogies to Human Speech

The larynx of birds differs significantly in its structure and function from that of mammals. The avian larynx forms a laryngeal chamber that is devoid of vocal folds, but instead affects the resonance of sounds that are generated in the syrinx at the base of the long trachea. It is movably attached by ligaments and extrinsic muscles to the basihyal-urohyal bone of the complex avian hyoid skeleton which is suspended cranially by extrinsic lingual muscles and fasciae to the mandible and caudally by hyoid horns within vaginal hyoid sheaths to the cervical fascia. In general, the avian larynx comprises a ring- or trough-shaped cricoid whose lateral limbs converge caudo-dorso-medially to form the crico-procricoid joint with the unpaired procricoid bone, which articulates rostrally with the bony bases of the paired arytenoids. The cartilaginous rostral parts of the arytenoids support the glottal lips, which are opened and closed by the intrinsic dilatator and constrictor muscles. Whereas the procricoid and ary...