This, if anomalous, may be:
- Broad (if greater than 133 mm.).
- Narrow (if less than 100 mm.).
- High (if over 60 mm.).
- Low (if under 50 mm.).
2. To the Symmetry of the Face.—If the face is notably asymmetrical, in respect to a plane dividing it longitudinally, the fact is at once perceptible. But a slight asymmetry may fail to be detected either by measurements (trago-mental diameters) or by inspection. Consequently, it will be well to follow certain practical rules in making this observation.
Observe first of all the median line of the face: the bridge of the nose, the nasal septum, the upper labial furrow and the point of the chin ought all to lie in the same vertical line; very often a slight deviation of the nasal septum above the upper labial furrow will betray the asymmetry; furthermore, the two naso-labial plicæ or folds should be noted, for they ought to be symmetrical in direction and in depth; lastly, we must observe the symmetry of the zygomatic prominences. We shall often discover three concurrent facts: a slight deviation in the median line of the face usually corresponding to the nasal septum; a greater depth of one of the naso-labial plicæ; and a greater prominence of the zygoma and the cheek on the same side.
Our attention should next be turned to the correspondence required by æsthetics between the following three diameters:
- Minimum frontal.
- Bizygomatic.
- Bigoniac.
A very notable difference between these distances may also lead to the discovery of anomalies.
Sometimes we may discover, even by inspection alone, a notable narrowness of the frontal diameter, as compared with the other two.
The bizygomatic diameter may show an exaggerated development, and this is frequently accompanied by a hollowness in the temporal and upper maxillary regions and by a beak-like prognathism (prominence of the middle portion of the upper maxilla); at other times this degenerative sign calls our attention to the mongoloid type.
The bigoniac diameter may also show an exaggerated development due to the enormous volume of the mandible (criminaloid type—Lombroso's assassin type). It is necessary to supplement our observation with the measurement of these three diameters, because it may very often appear to the eye that the minimum frontal diameter is below the normal, merely by comparison with the other two diameters which are overdeveloped; while when measured, it may turn out to be normal. Or, conversely, the other diameters, the bizygomatic or bigoniac, although actually normal, may appear overdeveloped, because of the shortness of the minimum frontal diameter (see "Faces of Inferior Type.")