Molecular analyses show that modern birds can be divided into two major taxa, the Paleognathae and the Neognathae. This division was already proposed by Merrem in 1813, based on morphological characters. One of the most prominent discriminating characters is the morphology of the Pterygoid-Palatinum Complex (PPC), which is different in paleognathous and neognathous birds. There are very few other morphological characters that support this division and even the differences in PPC have been under dispute. A discriminant analysis based on quantitative measurements of the PPC shows that a large difference between the two morphologies exists, and that the Tinamidae posses an intermediate form. An evolutionary maximum-likelihood analysis suggests that the PPC of the Paleognathae is more primitive than that of the Neognathae. A functional interpretation of the differences in the PPC between the Paleognathae and the Neognathae indicates that the paleognathous PPC is not, as generally accepted, an adaptation related to rhynchokinesis, but probably contributes to reinforcement of the skull after the loss of both the postorbital and nasal bar.