THE VERTEBRATE LARYNX - ADAPTATIONS AND ABERRATIONS

The complex anatomy of the vertebrate larynx shows a steady progressio n from the simple slit on the floor of the lungfish's pharynx to the f ine-tuned mechanism of the human vocal apparatus. The frog's larynx ac ts as a check valve to prevent collapse of the lungs during a dive, si nce the animal has no rib cage. The crocodile's laryngeal framework ha s acquired an epiglottic analogue which fits snugly into the nasophary nx and protects the lower respiratory tract from inundation while the animal drowns its prey. The snake's larynx lies intraorally and can be extended beyond the lower teeth while the reptile leisurely swallows its prey intact. The mammal has acquired a cricothyroid joint, allowin g its membranous vocal folds to be stretched during phonation. In Homo sapiens, vocal performance has reached its highest degree of versatil ity, with a vocal fold capable of adjustment in length, tension and sh ape. In the course of organic evolution, man appears to have chosen th e ability to speak and sing over the security that an intranarial epig lottis would have given him.