THE DESCRIPTION OF A NEANDERTHALOID AUSTRA-

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36 A. St N. Burkitt and J. I. Hunter The infraorbital fossa is an undivided depression. Of the specimens under review, it is exceeded in depth only in a Queensland skull, B. 10510 (Australian Museum), where there is a remarkable excavation undermining the infraorbital margin. That part of the zygomatic bone which enters into the formation of the margin of the orbit is not sharp but has a rounded bevelled border. Turner (19, p.32) says in regard to this point, "the orbits in the males were characterised both by the massiveness of the upper orbital border and by the peculiar breadth and curvature of- the malar bone where it formed the outer boundary, which wanted the sharpness one sees in crania generally." Klaatsch also directs attention to this feature for which he offers no explanation. For the following reasons we believe that the rounded character of the inferior orbital margin is due to the large size and great degree of wearing of the molar teeth often to be found in Australian aboriginals: Firstly, the rounding of the orbital margin is most marked in those skulls with a marked degree of wearing of the teeth. Klaatsch (12, p. 79) refers to R. 16 as showing a degree of wear corresponding to many pre-historic European skulls, and greater than that of any other aboriginal he had examined. In this skull the orbital margin is exceptionally well rounded. A survey of the collections under consideration, proves that this relationship exists in the majority of cases. Secondly, the bevelled or rounded condition of this border is not found in childhood and is only slightly present in early adult life in the specimens under review. It is apparently acquired therefore in adult life, following the usage of the permanent dentition. Thirdly, in those skulls in which the teeth were neither massive nor wellworn, the orbital margin was usually sharp, and the zygomatic bone was not massive (e.g. R. 12, R. 49). We, therefore, conclude that the amount of use of the molar teeth by a given individual, together with the massiveness of the teeth in the Australian aboriginal, contributes to the formation of a rounded orbital margin. There are exceptions to this, however, a sharp orbital margin sometimes being present, together with well-worn teeth. In these cases the masticatory apparatus was less well developed, the palate being usually narrow and the teeth comparatively small (R. 82). Features associated with this rounding of the margin, are a broadening of the cheek region and a lateral convexity of the zygomatic arch, as mentioned by Turner. This gives rise to the diamond-shaped appearance of the face often observed in the Australian aboriginal (Cunningham (6)). We consider also that these features are due in part to the operation of mechanical factors. The zygomatic bone is strengthened in order to accommodate the masticatory muscles and to support the force transmitted upwards by the molar teeth during grinding. So marked is the increase in bone formation in the case of R. 2 that a ridge is formed on the zygomatic
Description of a Neanderthaloid Australian Skull bone. It is directed antero-posteriorly so dividing the outer surface of the zygomatic bone into two portions. The upper of these two surfaces is separated from the orbital cavity by a smooth rolled border (the lateral and inferior margin of the orbit). In this case the massive molars are extensively worn. The zygomatic arch of No. 792 has an upward convexity, while the roots posteriorly form a plate which bears inferiorly an extension of the glenoid fossa. The thickness of this plate is 6 mm. compared with 9-10 mm. in Spy II. The lower border is irregular being distinctly notched by an impression for the masseter. There is a lateral convexity, the greatest inter-zygomatic diameter being in the temporal segment; this portion of the arch measures 11 mm. vertically and 5 mm. transversely. The strength of the zygomatic arch in the skull of the Australian aboriginal is to be correlated with the racial features exhibited by the facial skeleton. The Mechanism of Production of the Facial Characteristics of the Australian Aboriginal. The zygomatic arch forms a massive support for the masseter muscle while its lateral convexity increases the size of the temporal fossa to accommodate the other muscles of mastication. In addition to accommodating the masticatory muscles, this stout arch forms a buttress of support for the body of the zygomatic bone which receives and transmits the stresses and strains which it receives from the maxilla. Now the teeth of the aboriginal, which are usually massive, have to contend with a molluscan, fibrous and often gritty diet. On account of these factors, the maxilla must be of stouter structure and in consequence a general massiveness results. The molar teeth are mainly supported by the vertical ridge of the maxilla proceeding vertically upwards to the zygomatic process, while the canines and incisors (as in the gorilla) transmit their thrust through the frontal process of this bone. These columns. may increase in size to such an extent that the area above the premolars appears hollowed out, i.e., there is formed an infraorbital fossa (R. 2 and R. 24). In other cases this fossa may become deep through an actual excavation. In these cases the roots of the teeth may be divided into two sets as in R. 12. In this specimen the vertical ridge of the maxilla supports the roots of the molar teeth which converge towards it, while the roots of the premolars slope forwards towards the frontal process. When, however, the molar-premolar root arcade is uninterrupted in specimens which exhibit a tendency to squareness of the palate as in R. 10, R. 24, R. 35, R. 39, and R. 69, then the infraorbital fossa is often absent or very shallow. This is because force is transmitted vertically upwards to the infraorbital margin, between the main pillars of support. These features explain why all grades of development of the infraorbital fossa are possible in Australian skulls. In Australian aboriginals, the frontal process is usually stout and powerful. It supports the thrust of the incisors, canines and sometimes the premolars. The two frontal processes often approximate to one another being separated 37
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THE DESCRIPTION OF A NEANDERTHALOID AUSTRA-

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