Fig. 147.—Occipital norm.
Fig. 148.—Lateral norm.
The cranium must be observed from above, from the front, in profile and from the occipital part; and in such a manner that the observer's glance shall fall perpendicularly upon whichever cranial side is under observation. Hence it is said that the observation is made according to the norm, i.e., according to the perpendicular, and there are four norms in cranioscopy—vertical, frontal, lateral, and occipital. In this way we may be sure that no anomaly of form will escape the eye.
There are innumerable anomalies of form. We will indicate only the principal ones. In order to detect all the anomalies that may occur in a cranium it is necessary to observe it according to all the norms, each one of which may reveal a different set of anomalies.
A. Vertical Norm.—The word norm, as we have already said, has here the signification of perpendicular. To look at a cranium according to the vertical norm means to let our glance fall perpendicularly upon the vertex of the cranium. We may do this in one of two ways, either by raising our head above that of the subject of inspection, in such a way that our glance falls vertically upon it, or by bending back the head of the person to be observed until the crown of his head becomes perpendicular to our gaze. This norm is taken by placing oneself behind the person to be observed, who, if an adult, should be seated while the observer remains standing; and by taking the head to be examined between the two hands in such a way that the extended thumbs and index-fingers form a horizontal circlet around the cranial walls.
This is the most important of the norms, not only because it reveals the most important normal forms already described in the text, but also the greater number of anomalies such as are indicated below.
1. Crania with Rectilinear Perimeter.—It may happen that the line bounding the cranial vault is not curved but formed of broken straight lines from which various geometrical figures result, producing crania known as trigonocephalic, pentagonoid, parallelopipedoid, etc.