Summary: The postnatal growth of the maxillary sinus was analyzed in 20 male and 20 female skulls of orang-utan (Pongo satyrus borneensis) in 5 age steps. Coronal CT scans were carried out of all skulls using a computed tomograph Siemens SOMATOM DR. The distances between the CT scans were always 4 mm. The outline of the maxillary sinus was surrounded on the CT scans with a planimeter and then the volumes were calculated. Using a growth model introduced by Fanghariel (1974), growth functions for the volume measurements for male anf female animals were calculated separately. The growth curves showed a particular course, which was characterized by a quick rise until the age of 15 years. After the age of 20 years the curves for females orang-utan became gradually flat. At the age of 21 to 23 years the confidence intervals of the growth curves for male and female orang-utan began to drift apart, indicating the appearance of a sexual dimorphism. Using the basicranial length as an indicator of skull size, it becomes evident, that the sexual difference in the maxillary sinus' volume is probably based on the fact, that the maxillary sinus' volume of the male orang-utan increases further on following a common growth pattern.

In contrast to the paranasal sinuses of Old World monkeys and hominoids, little information is available about the paranasal sinuses of New World monkeys. Because this information is crucial in order to draw further conclusions about the evolution and biological role of skull pneumatization, this study investigates the morphology of the paranasal sinuses in adult black-and-gold howler monkeys (Alouatta caraya). Volumes of the paranasal sinuses were calculated using computer software (SURFdriver or Allegro) from serial coronal CT scans of 20 skulls of both sexes. Skull pneumatization in A. caraya is more complex than in other higher primates. In both sexes, the maxillary sinus (MS) is the only pneumatic cavity and enlarges regularly into neighboring bones such as the frontal bone and the basisphenoid. The resulting pansinus is often partitioned by several vertical septa. As in most external cranial dimensions, mean MS volume of A. caraya (male 4.08 cm(3); female 2.00 cm(3)) shows significant sexual dimorphism. Reduced major axis regression analysis between MS volume and different cranial dimensions for A. caraya (and for available data from other platyrrhines) suggests a distinct association for this group, with Alouatta having one of the largest pneumatic cavities. The combination of this unusual expansion of the MS of Alouatta and the occurrence of distinct septa within the sinus may be a consequence of the distinct skull architecture of Alouatta.

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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.

In a mixed sex sample of ten adult gibbon (Hylobates moloch) skulls, one cranium of a male with maxillary sinus atelectasis of the left side was identified. While external inspection revealed a slight drop of the left orbital floor, serial coronal computer tomography (CT) scans show characteristic changes of the left maxillary sinus and its surrounding structures. In addition to the sunken orbital floor, radiological features of the specimen include an inward bowing of the medial sinus wall, sinus opacification, and a reduction in maxillary sinus size to a slit-like cavity, which suggest a diagnosis of silent sinus syndrome. This report is the first, to our knowledge, of maxillary sinus atelectasis in a non-human primate. This finding is valuable for the understanding of the pathogenesis and etiology of maxillary sinus atelectasis. At the same time, however, paleoanthropologists and primatologists may refer to this information when dealing with the interpretation of maxillary sinus pneumatization of partially broken archaeological and fossil skulls.