42. Growth‐changes in the Skull of the Baboon, Papio porcarivs*

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Abstract
Summary.: The prosthion‐inion length, the transverse diameter, and the basi‐bregmatic height continue to increase from birth until a time considerably subsequent to the eruption of the permanent teeth. The varying proportions of face to cranium at the different stages of growth are demonstrated in the text and diagrams. Virtually all the cranial sutures of the Baboon skull, unlike those of the higher anthropoids, are never completely occluded, even in the aged male. The basicranial axis and its angles are of a type which finds its closest counterpart in those of the anthropoids. The spheno‐maxillary angle in the Baboon has an average value of 90° 30′, and is therefore well within the human range. This angle, far from being “the most important angular measurement by which prognathism can be represented” (Duckworth), is worthless as a criterion of prognathism. It does, however, indicate the degree of “subgnathism.” The spheno‐maxillary angle in the Baboon does not increase with the eruption of the permanent teeth and with the growth of the muzzle. This lack of increase during growth is explained by a downward rotation of the muzzle upon the basi‐cranial axis. Flower's gnathic index is shown to be a reasonable criterion of the degree of prognathism in the Baboon skull. Prognathism in the Baboon has been studied by means of the facial triangle (text‐fig. 7 and Table III.), which, in my opinion, expresses most clearly its nature and degree. The growth‐changes in the cephalic index, temporal lines temporal fossæ, nuchal area, occipital plane, base of skull, and palatal and alveolar dimensions are of a nature comparable with the growth‐changes in the higher anthropoids. An increase of 22 per cent. occurs in the volume of the endocranial cavity in the male Baboon, and 4 per cent. in the female, between the period of milk dentition and maturity. This later brain‐growth takes place chiefly in the temporal lobes and cerebellum, and very slightly in the length and breadth of the cerebrum. No growth at all takes place in the height of the cerebrum above the subcerebral plane after the period of the milk dentition. In conclusion I wish to express my indebtedness to Professor M. R. Drennan for his kindly advice and criticism during the progress of the investigation, and to Professor Raymond A. Dart, of the University of the Witwatersrand, for reading a draft of the paper and for valuable advice.

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