1367 
zi: min. 7.47 mm., max. 11.87 mm., average 10.45 mm. 
wo: With only slight oscillations, average — 15.27 mm. 
Yo: min. 2.01 mm., max. 22.90 wm., average 12.30 mm. (8.24 mm. 
zo: with only slight oscillations, average 12.25 mm. 
From the location of the trochlea and of the point of insertion 
of the m. obliquus superior we can calculate the position of the 
plane in which the couple lies that is formed by contraction of this 
muscle. We shall call this plane the plane of motion. The axis of 
motion of this muscle stands in the center of rotation perpendi- 
cular to this plane of motion. The plane of motion does not entirely 
correspond with the muscle-plane, which is defined as the plane 
going through the trochlea, the point of insertion of the muscle and 
the central point of the eye. The plane of motion namely goes 
through the trochlea, the tangential-point of the muscle and the 
point of rotation of the eye; by the tangential point we understand 
the point where the muscle first touches the bulbus oculi. L should 
consequently be obliged first to calenlate the location of the tangen- 
tialpoint; for simplicity’s sake, however, I have not done so and 
admitted as plane of motion the plane going through the trochlea, 
the point of insertion of the muscle and the center of rotation of 
the eye, as this can occasion only an ifisignificant error. By means 
of this plane I bave caleulated the location of the axis. 
Now we can calculate the location of the axis of motion for the 
averages and for all combinations of the different extremes. These 
calculations have been made by me for six cases; these cases we 
call a, b,c, d,e and 7. With a and / the averages have been used, 
only y, is in the: two cases different. 
For e | took “@q as large as possible, 7; as large as possible, 
yi as small as possible. In this eye we may expect: a strong rotation, 
a feeble abduction, a feeble deorsumduction. 
For d. 1 took 7 q as large as possible, a as small as possible 
yi as large as possible. In this eye we may expect: a strong rotation, 
a strong abduction, a feeble deorsumduction. 
For e I took q as small as possible, 2; as large as possible, 
yi as small as possible. In this eye we may expect: a feeble rotation, 
a feeble abduction, a strong deorsumduction. 
For f I took 7“ q as small as possible, 7; as small as possible 
yi as large as possible. In this eye we may expect: a feeble rotation, 
a strong abduction, a strong deorsumduction. 
Just like VorKMANN I shall call the angle of the axis of motion 
with the z-axis ~ 4, with the y-axis / uw and with the z-axis / rv, 
