Abstract
The experimental work discussed in this paper was undertaken to study the relative effects on the growth and development of the mandible and maxilla of the rat of indolent as compared to vigorous masticatory function. Are the broad, well developed arches of primitive races the result of increased function, or are they due to their hereditary background? Or conversely, is the frail development of the supporting structures of the teeth of modern people the result of their soft, non-stimulating, highly refined diets?