any affectation of attitude, but because it is less wearisome to the eyes to assume this position. As a matter of fact this person's eyes were normally adjusted 10° below the plane which has been found to be the
best and which may be called the standard plane. On the contrary the person whose pose is represented at Fig. 13, whose head is high compared to its transverse and horizontal diameters, a head which is neither of the long nor broad type, but of the medium (tall) type with the absence of a strong angle of the face, had the plane of vision very high. Such a person prefers to throw the forehead in advance and the chin into the breast, rather than make a continual and somewhat tiresome effort to draw the eyes to the proper plane by direct tension upon the depressor muscles of the eyes.
It is not difficult to see that this selection of the easiest method of adjusting the lines of sight to surrounding objects exercises a commanding influence on the whole pose of the body.
While the rule generally holds that the form of the skull and therefore the form of the orbit governs the direction of the visual plane and hence also the pose of the head and of the body, there are other elements which enter into the case and give rise to exceptions. The most important of these modifying elements is the condition known as the 'declination of the vertical meridians of the retina';[1] still, in order
- ↑ The subject of the horopter has already been referred to in the note to page 395. In regard to declinations, while it would be impossible to enter upon that complex subject here, it would be misleading were we to pass it by without the statement that the pose of the head is sometimes governed, even against the rule which it is sought here to point out, by the direction of the retinal meridians and hence in practice a knowledge of this subject would be essential to a full understanding of the subject under discussion.
