THE POSE OF THE BODY. 393 



In these three classes of crania the normal visual plane does not as 

 a rule occupy the same position in relation to the horizontal plane, but 

 varies according to the type of skull. 



The relation of the normal visual plane to the type of tne cranium 

 in each of the three classes may be arrived at by direct and by indirect 

 methods. 



In the case of the living subject, the dimensions of the head may be 

 taken and the plane of vision established in the same individual. The 

 determination of the plane of vision in the living subject is accom- 

 plished through the aid of an instrument known as the tropometer. 

 The relation is thus established by a direct method. The indirect 

 method is that of ascertaining the direction of the imaginary line con- 

 stituting the axis of the orbit in 

 the prepared skull, the measure- 

 ments of which are known. The 

 orbits are more or less cone- 

 shaped. If the extreme apex of 

 the cone, at which the optic nerve 

 enters it, is taken as one point of 

 the line of the axis, and a point 

 where two straight lines drawn at 

 nearly right angles with each - — -^ ^ 



other from certain parts of the ^"' ''■ ^he author's method of deter- 



•^ MINING THE Axis of the Orbit. 



Circle of bone constituting the 



outer border of the orbit cross is taken as another point in the line of 

 the axis, the line which would pass through these two points would 

 represent the axis. This imaginary line, if projected forward and be- 

 yond the orbit, would be seen in most cases to point somewhat down- 

 ward, the skull being in the primary position, and in some types of 

 skulls it points much more downward than in other types. 



It is interesting to find that the pointing of the imaginary line rep- 

 resenting the axis of the orbit closely corresponds with the observations 

 on the normal visual plane in the living subject. 



The interest is more considerable when it is found that the form of 

 the orbit in the different classes of skulls offers an explanation of the 

 peculiarities in the direction of the orbital axis, as well as of the 

 normal plane of vision. 



Figs. 8, 9 and 10 represent the front views of skulls of the long, 

 tall and broad types respectively, showing the form of the orbit corre- 

 sponding to each type. It will be seen that in the long skull (Fig. 8) 

 the roof of the orbit is much lower than that of the tall skull (Fig. 9) 

 and that the lower border extends more downward. The orbit of the 

 tall skull is not only placed with its opening higher, but it is more 

 narrow from side to side. In the case of the broad skull (Fig. 10) the 



