The most important among these and among all the abnormal forms is the trigonocephalic cranium, having the base of the triangle toward the occiput and the vertex toward the forehead. The result of such formation is that the frontal region is restricted, a circumstance of obvious gravity. The infantile cranium is normally pentagonoid; the persistence of this form in the adult is a sign of arrested development, but not serious. Sergi does not admit this form among the anomalies when the nodules are but slightly emphasised.
2. Asymmetrical and Plagiocephalic Crania.—The sagittal plane divides the cranium into two unequal halves. The asymmetry may be either frontal, in which case one frontal nodule is more prominent than the other—anterior plagiocephaly, or else parietal, in which case one of the parietal nodules is more prominent than the other—posterior plagiocephaly.
These are the two forms of simple plagiocephaly. It may happen that there is simultaneously an anterior and posterior asymmetry, and in such a case it generally happens that if the more prominent frontal nodule is on the right, the more prominent parietal nodule is on the left, so that the two more prominent nodules correspond in a diagonal sense. This is compound plagiocephaly.
Plagiocephaly is extremely common; if very apparent, it constitutes a grave defect, but not if only slight. For that matter, it would be difficult to find a cranium rigorously symmetrical, even among normal persons.
3. Crania with curved and symmetrical lines, but in which the perimeter consists not of a single ellipsoidal curve, but of two curves.
a. Clinocephalic Cranium.—The coronal suture has a girdle-like furrow, in such fashion that there result an anterior and a posterior curve which together form a sort of figure 8. This anomaly may be perceived also from the lateral norm.
b. Cymbocephalic Cranium.—- There is a girdle-like furrow along the sagittal line, so that the cranium has the appearance of being divided into two pockets, one on the right hand and the other on the left.
B. Lateral Norm.—The observer must stand at the side of the subject to be observed and look at him perpendicularly to the profile.
We remain standing while we look if the subject is an adult and is standing up, but we sit down if the subject is a child and is standing; and we determine the vertical position by moving the subject's head as the occasion requires.