THE INFRAORBITAL FORAMEN IN THE HOMINOIDEA

Abstract

SUMMARY The numbers and arrangement of infraorbital foramina have been recorded, and their position relative to the orbital and alveolar margins defined by measurement in 205 gorillas, 178 chimpanzees, 82 orangutans, 64 gibbons and 192 men of various ages. In man there are, on an average, 1·05 infraorbital foramina in each maxilla; in the gibbon 1·2; in the gorilla 1·6; in the chimpanzee 2·4; and in the orang‐utan 3·3. In adult men and gibbons the distance between the infraorbital foramen and the orbital margin is about twenty per cent of that between the foramen and the alveolar margin. The corresponding figure for the gorilla is forty‐five per cent, for the chimpanzee forty per cent and for the orang‐utan thirty‐five per cent. The arrangement of the infraorbital apertures varies widely both within and between species. While the milk teeth are erupting, the infraorbital foramen lies relatively nearer to the inferior orbital margin than in adults. In man, chimpanzee and gorilla, the adult position is reached by the time the first permanent molars are in line. In the orang‐utan, the position of the foramen apparently continues to change until maturity is reached. The numbers and arrangement of the infraorbital foramina are not correlated with the more obvious facial features (such as degree of prognathism), nor with variation in the basic subdivisions of the infraorbital nerve. The position of the foramen relative to the orbital and alveolar margins is closely related to the degree of prognathism. Although a single aperture appears to have occurred more frequently in the Australopithecinae than in the extant great apes, the foramen in these fossils lay in a position characteristic of the gorilla, and much further down the facial skeleton than in either modern man or the extinct species Homo neander‐thalensis.