[Illustration: FIG. 71.--Spheroid cranium.]
=Sub-varieties.=--_Sphenoids_ _trapezoids_, or _trapezoid cranium_. Observed from the vertical norm, this form appears as a variety of the _sphenoid_; and when seen laterally it is characterised by the lines of its contour forming a _trapezium_. Starting from the vertex of the cranium one line slants toward the forehead and another toward the occiput, which is very massive. In the figure given below, the quadrangle drawn in solid lines serves to indicate the correct position of the cranium, while the trapezium formed of dotted lines gives us its characteristic form.
[Illustration: FIG. 72.--Trapezoid cranium.]
Among the forms described by Sergi, are several which were formerly held to be abnormal, such, for instance, as the _platycephalic_ _cranium_ and the _pentagonoid_. Similarly, when the surfaces of the cranium showed a tendency toward flatness, or when there were cranial protuberances, even though these were destined to disappear, they were regarded as malformations. Before this high authority offered us his guidance, there were certain forms, frequently encountered, that it was difficult to define, for example, the trapezoid cranium, which often presents a notable vertico-occipital flattening, with the vertex notably higher than the forehead.
There are also certain forms of cranium having the frontal region more restricted than the parietal region, or slanting down from a much elevated vertex, which have been proved to be _normal forms_; while still another error previously made was that of trying to judge the _forehead_ on the criterion of a single model, deviations from which were much too readily relegated to the category of abnormalities. The most regular and beautiful forms, and the ones that are commonest in our racial stocks are the ellipsoid, ovoid and sphenoid. In my work on the women of Latium, precisely one of the points that I noted was the frequent occurrence of certain sub-varieties of the _ellipsoid_ and the _sphenoid_.
In order to recognise the _forms of the cranium_, a certain training is necessary which each one must acquire for himself. Observations of the cranium will make it easier to judge of the form in relation to the _head_, at least, when the latter is not too much hidden by the hair, as often happens in the case of young children.