In the case of the long head, for example, the angle is external, as will be seen on turning to the diagram, Fig. 4, in which the facial
general association between the character of the face and the type of the head.
Now, if the angle of the face is taken in connection with the type of head, we have a fairly certain indication of the direction of the plane of vision.
With the long head and strong external facial angle the plane of vision is almost invariably low. With the broad head and inverse angle the visual plane is also low, but there is a restricted downward range of the rotations of the eyes, notwithstanding this depressed position of the visual plane. With the tall head and straight face the plane of vision is high and in proportion as the head is comparatively tall it may be very high.
When these elemental principles are once understood it is not difficult to comprehend the phenomena to which they give rise.
Thus it is easy to see that a person whose normal plane of vision is quite low finds it easier to throw the head backwards, lifting the chin and forcing the forehead back, than to raise the visual plane to the level of the horizon or even to the lower plane which the eyes assume in walking, if that visual plane has to be thus elevated and the elevation maintained for some time by the delicate muscles which act directly in elevating the eyes.* On the contrary one whose visual plane is very high prefers to throw the forehead in advance and the chin into the breast rather than maintain a tension upon the little muscles which act directly upon the eyes to pull them down.
Thus it will be seen that the person represented at Fig. 12, with the long head (from before backward) and the strong angle of the face, carries the forehead quite far back and the chin well up, not from
- There is more in this statement than would at first appear, for the important question of the horopter must be included here, but this would add an element too extensive for present discussion.