Abstract
The tongue plays various important roles in the development process of the eating and swallowing functions which are acquired by infants. Few researchers, however, have objectively evaluated the developmental changes of the tongue movement during the transitional period from sucking to swallowing. In the present study, the tongue movement in infants from the 20 th to the 52 nd week of age was ultrasonographically observed and the frontal section of the dorsal surface was visualized from the submandibular part. Furthermore, the developmental changes of the tongue movement in the course of time were qualitatively analyzed.
1. In the 20 th week, a U-shaped hollow was formed on the dorsal surface during swallowing. Generally the tongue corpus showed a simple up-and-down movement.
2. In the 26 th week, a central groove was formed in the median part of the dorsal surface during swallowing.
3. In the 35 th week, the right and left margins of the dorsal surface of the tongue touched the palatal sides of the alveolar ridges corresponding to the upper posterior teeth, and the median part of the dorsal surface simultaneously showed the tongue central groove formation movement.
4. During the period from the 35 th to the 52 nd week, the uniformly stabilized the tongue central groove formation movement of the median part of the dorsal surface of the tongue was repeatedly observed.
5. The changes in the tongue central groove formed by the alimentary bolus in the median part of the dorsal surface of the tongue were carefully observed in the course of time and the development changes of the tongue movement were classified into the following six stages; resting, preparing, central groove forming, central groove disappearing, palate pressing and repositioning stages.
The Coronal section of the dorsal surface of the tongue was used to study the development process of the tongue movement. The right and left margins of the tongue touched the palatal sides of alveolar ridges and were fixed there.
The tongue central grooving for alimentary bolus formation was observed in the areas ranging from these contact fixation points toward the median part of the dorsal surface of the tongue. This detailed observation of the tongue central grooving formation process contributed significantly to the kinetic analysis of lingual food transportation movement at the time of swallowing.
