Meeting Abstract
Birds have a long neck that can be extended or retracted into an S-shape, but little is known how these movements affect the positions of its organs (vertebral column, trachea, esophagus, cervico-cephalic air sacs, and cervical envelope). The functional morphology of the cervical apparatus was studied by using microdissection, 3D modeling based on CT data, and animation of a 3D model by matching it with x-ray videos of singing birds. In songbirds (e.g., the House Sparrow), the neck is usually extended and the tongue is moved back-and-forth during singing. When the hyoid apparatus and, thus, the larynx and trachea are protracted, the neck expands and the cervical envelope is stretched. When the hyoid, larynx, and trachea are retracted, the neck tightens and the cervical envelope contracts. These configurational changes are enabled by the cervical coelomic cavity in which the trachea and esophagus are tethered to the vertebral column by mesenteries. The paired cervico-cephalic air sacs within the coelomic cavity are inferred to inflate and fill the increased volume when the neck expands. The cervical skin bears narrow dorsal and ventral pterylae that are separated by lateral apteria with circular smooth dermal muscles. Circular and longitudinal striated cutaneous muscles are built into an underlying fascial system. Together, the dermal and cutaneous muscles regulate the tension and resonating properties of the cervical envelope which, therefore, can be tuned to the frequency of sounds generated by the syrinx and traveling through the trachea. The anisotropic cervical skin, tunable cervical envelope, and cervico-cephalic air sacs of songbirds create a sound resonating system that is analogous to the tonal drums of India. Supported by NIH grant NINDS R01 NS029467 and the LSU Foundation
