If now we see a skull lengthwise, or draw a projection of it, and connect the glabella and the inion by a line GI, and the glabella and the bregma by a line GB, an acute angle, BGI, is formed. This is the “bregma angle.” Obviously a high vaulted skull or one that has the superior point B well forward will show a greater angle than a low flat skull or one with its summit lying far back.
Fig. 7. Indices and angles of special significance in the change from fossil to living man. Calvarial height index, BX: GI. Bregma position index, GX: GI. Bregma angle, BGI. Frontal angle, FGI.
Next, let us drop a vertical from the bregma to the line GI, cutting it at X. Obviously the proportion which the vertical line BX bears to the horizontal line GI will be greater or less as the arch or vault of the brain case is higher or lower. This proportion BX: GI, expressed in percentages, is the “calvarial height index.”
The Skull of Modern and Fossil Man
| Calvarial Height Index | Bregma Angle | Bregma Position Index | Frontal Angle | |
|---|---|---|---|---|
| Maximum for modern man | 68 | 66 | ||
| Average for modern man | 59 | 58 | 30.5 | 90 |
| 90 Central Europeans | 60 | 61 | 31 | |
| 28 Bantu Negroes | 59 | 59 | 31 | |
| 7 Greenland Eskimos | 56 | 58 | 30 | |
| 43 Australian natives | 56 | 57.5 | (33) | |
| 8 Tasmanian natives | 56 | 57 | ||
| Minimum for modern man | 47.5 | 46 | 37 | 72 |
| Chancelade | 57 | 60 | ||
| Combe-Capelle | 54.5 | 58 | ||
| Aurignac | 54.5 | |||
| Cro-Magnon I | 50 | 54 | 33 | |
| Brünn I | 51 | 52 | 75 | |
| Galley Hill | 48 | 52 | 82 | |
| Brüx | 48 | 51? | 75? | |
| Le Moustier | 47 | |||
| Krapina C | 46 | 52 | 70 | |
| Spy II | 44 | 50 | 35 | 67 |
| Krapina D | 42 | 50 | 32 | 66 |
| Chapelle-aux-Saints | 40.5 | 45.5 | 36.5 | 65 |
| Spy I | 41 | 45 | 35 | 57.5 |
| Gibraltar | 40 | 50 | 73? | |
| Neandertal | 40 | 44 | 38 | 62 |
| Pithecanthropus | 34 | 38 | 42 | 52.5 |
| Maximum for any Anthropoid ape | 38 | 39.5 | 63 | |
| Chimpanzee | 32 | 34 | 47 | 56 |
| Gorilla | 20 | 22 | 42 | |
| Orang-utan | 27 | 32 | 45 | |
| Summarized Averages | ||||
| Modern races | 59 | 58 | 31 | 90 |
| Cro-Magnon race | 54 | 57 | 33 | |
| Brünn race | 49 | 52 | 77 | |
| Neandertal man | 42 | 48 | 35 | 66 |
| Pithecanthropus | 34 | 38 | 42 | 52 |
| Anthropoid apes | 26 | 30 | 45 | |
If now we compute the proportion of the GX part of the line GI to the whole of this line, we have the “bregma position index”; that is, a numerical indication of how far forward on the skull the highest point B lies. A sloping or retreating forehead naturally tends to have the bregma rearward; whereas if the frontal bone is nearly vertical, resulting in a high, domed expanse of forehead, the bregma tends to be situated farther forward, the point X shifts in the same direction, the distance GX becomes shorter in comparison to the whole line GI, and the “bregma position index” falls numerically.
The “frontal angle,” finally, is determined by drawing a line GF from the glabella tangent to the most protruding part of the frontal bone and measuring the angle between this and the horizontal GI. A small frontal angle obviously means a receding forehead.