Regression of Intermediate Functions

a particular case of the transformation of an organ in phylogenetic development, in which the organ’s primary function is intensified at the expense of regression of the intermediate function. This type of change in organs was established by A. N. Severtsov. An example of the regression of an intermediate function is the formation in mammals and humans of a new connection of the lower jaw directly to the cranium through the dentary bone (this intensified its function) instead of through the quadrate bone and the articulare (which shifted to the middle ear). This made it possible to chew food in the mouth.