Meanwhile we must not forget that the following are signs of grave degeneration:
a. The minimum frontal diameter less than 100 mm. (the gravity of this is increased if at the same time the other two diameters are found as described in b).
b. The other two diameters greater than 110 mm. (Lombroso's born delinquents, assassin type).
Lateral Norm, or Norm of Profile.—Our attention ought to be directed, as we have already said:
1. To the direction of the forehead. If abnormal, this may be:
- a. Receding;
- b. Bombé.
The receding forehead is an indication of an incomplete or defective development of the frontal lobe of the brain; we find the forehead notably receding in the microcephalic type.
The bombé forehead is characteristic of hydrocephaly, but may occur also in the scaphoid cranium. When the forehead is bombé, the facial angle becomes equal to or greater than a right angle, because the face recedes beneath the extreme anterior boundary of the brain; in this case we have the opposite case to prothognathism, namely, orthognathism.
2. Our attention should next be directed to the facial profile, in order to observe the form and degree of prognathism.
The authorities distinguish three principal forms of prognathism: