Numerous investigators have pointed out that the force of the tongue against the teeth within the dental arches is normally compensated for by the action of the musculature of the cheeks and lips, and that the tongue at rest occupies a large part of the oral cavity. The purpose of this study was to estimate the maximum areas of the tongue movement by measuring the inner area of the dental arches of both the maxilla and the mandible. This study was based on the study models of 30 children and 128 adults who had clinically good occlusion. There were 15 male and 15 female children whose ages ranged from four years to seven years and 82 male and 46 female adults whose ages ranged from fifteen years to fifty four years. The obtained results were as follows : 1. The mean of the maximum areas within the primary dental arches of both the maxilla and the mandible were $7.06pm0.8 extrm{cm}^2, 5.49pm0.77 extrm{cm}^2$ in male children and $6.82pm0.98 extrm{cm}^2, 5.28pm0.80 extrm{cm}^2$ in female children respectively. 2. The mean of the maximum areas within the permanent dental arches of both the maxilla and mandible were $17.01pm2.38 extrm{cm}^2, 13.57pm1.57 extrm{cm}^2$ in male and $16.75pm2.08 extrm{cm}^2, 13.36pm1.01 extrm{cm}^2$ in female respectively.