396 



POPULAR SCIENCE MONTHLY. 



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 



Fig. 12. 



Fig. 13. 



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 com- 

 pared 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 tire- 

 some 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 com- 

 manding influence on the whole pose of the body. 



While the rule generally holds that the form of the skull and there- 

 fore 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 ele- 

 ments 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';* 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 t*he 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. 



