THE POSE OF THE BODY. 391 



By the term 'normal plane of vision/ as here employed, it is in- 

 tended to express the direction which the lines of sight would assume, 

 the head being in the erect, or more technically in what is known 

 as the 'primary, position, in case no muscular effort should be made to 

 change the eyes from an entirely passive adjustment. 



Under these conditions the line of sight of each of the two eyes lies 

 in an imaginary plane which may be coincident with, or somewhat 

 higher than, or somewhat lower than, the plane of the horizon. 



The normal plane of vision differs essentially from the primary 

 plane of regard of Helmholtz and other writers, for this plane of regard 

 refers to the plane formed by the two visual lines when these lines are 

 directed toward the horizon, the head being in the primary position. 

 The plane of regard is therefore unalterable. It was my own privilege 

 to show that the normal plane of vision not only varies in different 

 individuals but that, as a general rule, this variation is associated with 

 and controlled by certain cranial characteristics which will presently 

 engage our attention.* 



This leads us to the consideration of certain types of the human 

 cranium as they are recognized by craniologists. 



While the form of the head of an individual may not be so clearly 

 of one or another type that it must be classified as belonging to a cer- 

 tain group, in general, heads are grouped into three great classes or 

 types, and these classes or types are again divided into subtypes. In 

 this connection the subtypes need not be taken into consideration, but 

 some knowledge of the main types is essential. 



Craniologists,. then, classify crania as long, hroad and medium. 

 Medium skulls, in order to avoid misconception, will be here designated 

 as tall skulls, since the term medium does' not, in this relation, refer to 

 capacity, but to certain special measurements, and the accepted term 

 might be misleading to those not well versed in the subject. 



The basis for the classification consists of the proportion which the 

 longest diameter from before backwards bears to the longest transverse 

 diameter. If the transverse diameter is ^Vioo that of the longer 

 diameter or less than '^Viooj the head is said to be in the class of long 

 heads ; but if the transverse diameter equals or exceeds ^ Vioo the length 

 of the skull, it is a broad skull. Medium skulls, or, as we are now to call 

 them, tall skulls, are those in which the transverse diameter is between 

 "/loo and ^Vioo and, as might be supposed, the measurement from the 

 base of the skull to its summit, while it may not of itself be greater in 

 an individual case than that of one of the long or one of the broad type 

 nor even so great, is greater in proportion to the other measurements. 



* The Normal Plane of Vision in Relation to Certain Cranial Character- 

 istics. 'Archives of Ophthalmology,' Vol. xxvi, No. 3, 1897. 



