contrary of such a nature, that the line of vision lies in the plane 
of motion of the m. obiq. sup., a contraction of this muscle would 
move the eye downward without rotation. This view cannot 
be entirely correct. We may not first let an abducing or adducing 
force operate and afterwards let the m. obliq. sup. operate, as if 
nothing had happened to the eye. We could as well first let the 
in. obliq. sup. operate and then let an abducing or adducing force 
influence. The result, the position of the eye, would then be quite 
different. In the two cases the tensions of the muscles might be equal, 
the resultant of the tensions of the tissues unequal; it is impossible 
that there could be equilibrium in both cases. We come nearer 
to the truth, if we ask ourselves, what is the resultant of the two 
muscle-tensions, how is the plane of motion of this resultant located? 
The eye will namely assume a position, as if it had come into this 
new position from its primary position, through the resultant of 
these muscle-tensions. For simplicity’s sake I let here the primary 
position coincide with the anatomical position of rest of the eye. 
The axis of the resultant will be located in the plane going 
through tbe axes of the two components. When the m. obliq. sup. 
cooperates with an abducing or adducing force, the planes of motion 
of resultant and components will always cut each other in one line, 
whatever the relation of the forces may be. With abduction the 
y-axis is located over the plane of motion of the resultant, with 
adduction under it. A result of this fact is, that with cooperation 
of the m. oblig. sup. with an abducing force the deorsumduction is 
much less important, than with cooperation with an adducing force. 
If the abducing force = Aj, the adducing force = — Aj, the resulting 
force —K,, and the location of the resulting axis determined by 
the angles 4, (with z-axis) mw, (witb y-axis) and vr, (with z-axis) then 
the following formulae hold: 
KE Or EKA a Keos 
KG sin v 
tg vy = ——- 
KG =\- Ky Cos Y 
sin YP, COs 2 sun Vr COS U 
OSS. ae cos Ur = — 
sun r sin ry 
In the normal eye, it has already been discussed, the cooperation 
of the muscles will always be such, that the eye assumes such a 
position, as if it had eome into that position by rotation round an 
axis in the plane of Listinc. This is no more true for the extreme 
limits of the field of vision, and neither with convergention. The 
law of Listing makes it necessary, that the resultant of the moments 
