The inferior frontal triangle a new cranial triangle. Three new cranial indices the relative proportions of the three sides of the inferior frontal triangle in man and the anthropoids. The inferior frontal triangle as an index of evolutionary activity in the region of the frontal cranial arc. Craniometric studies, 33, 34, 35
American Journal of Phys Anthrop 17(1): 99-110, 111-116, 117-121
33. This is a new cranial triangle devised by the author. The 3 sides exhibit small though definite and consistent increases of their average lengths in the Hamann Museum [male] white skull, as contrasted with the Hamann Museum [male] negro skull. The evolutionary advantage in favor of the whites is, however, not so great as one would have expected. The 3 constituent angles of this triangle show very small racial differences in the negro crania, as compared with the white crania. Therefore, the general shape and configuration of this triangle are not very different in these 2 cranial groups.[long dash]34. The relative proportions of the 3 sides of this triangle provided 3 new cranial indices which are described for the first time. The H-G/P-G index was consistently lower in the Simiidae than in man, and thus tended to increase as one ascended the evolutionary scale. This increase was due to the evolutionary expansion of the lower half of the frontal cranial arc to provide accommodation for the developing frontal lobes of the brain. It was difficult to assign any degree of evolutionary importance to the H-G/P-H index. The P-G/P-H index was lower in the Hominidae than in the Simiidae. This indicated that the P-H dimension was increasing relatively to the P-G dimension as one ascended the evolutionary scale. This in its turn showed that the evolutionary growth leading to the expansion of the frontal cranial arc in a forward direction was more active in its middle section than in its lowest section.[long dash]35. This triangle undergoes great expansion in the higher races of mankind. It is therefore a very-valuable index of evolutionary activity in the region of the frontal cranial arc. Throughout the Simiidae, from the lowest to the highest members of the group, one can recognize the steady advance of this evolutionary process. It is significant, however, to note that a very decided evolutionary gap existed between the Hominidae and the Simiidae.