ABSTRACT
Also at about 3 months of life the infant rib cage is restructured to approximate the adult configuration (Langlois, Baken, & Wilder, 1980). In newborns the ribs are almost perpendicular to the rib cage, which prevents them from sustaining the steady subglottal pressure necessary to produce long episodes of phonation. In adults, this is achieved by the inspiratory function of the intercostal muscles as a mechanical consequence of the downward and outward angle of the ribs from the spine. Thus the anatomical restructuring that occurs by approximately 3 months of age facilitates the production of adult human speech (Lieberman, in press).
