The relationship between the palatal form and the maxillary sinus in orang-utan.

The relationship between the palatal form and the maxillary sinus was studied in 40 skulls of male and female Bornean orangutans (Pongo satyrus borneensis) ontogenetically. Univariate analyses of the measurements of the palate and the maxillary sinus showed that the sexual dimorphism appeared earlier in palatal length than in the maxillary sinus volume. Bivariate statistical analyses, including correlation and linear regression analyses, revealed close relationships between the characteristics of the palate and the maxillary sinus for both the growth period and the adult status. Partial correlation coefficients showed, however, that these relations were highly influenced by the skull size. Except significant correlations between the maxillary sinus width and the palatal volume in the adult status, all partial correlation coefficients were clearly below the Pearson's correlation coefficients. In contrast to the situation in humans, this study suggests that under physiological conditions the influence of the palatal form on the maxillary sinus size in the orang-utan is very small. Alterations of the craniofacial morphology during the evolution of the hominids, such as facial reduction and decrease of the maxillary sinus size, are considered important factors which led to changes of the relations between the palatal form and the maxillary sinus.