We shall only then speak of rotat/on in case the eye makes 
a motion or assumes a position that does not correspond with the 
law of Listinc. The rotation is then measured by the angle through 
which the eye must rotate round the line of vision as axis to answer 
to the law of Listing. 
By abduction and adduction | shall understand the smailest angle 
that the line of vision makes with the sagittal plane. 
By deorsumduction and sursumduction 1 shall understand the 
smallest angle that the line of vision makes with the horizontal 
plane. 
The extent of the rotation will depend upon the angle between 
y-axis and axis of motion and of the excursion that the eye has 
made round the axis of motion. 
We can express this in the formula: tg.'/, R=cosutg. '/, #, 
in which / R = rotation, / u — angle between y-axis and axis of 
motion, “ /'= excursion. 
For the abduction holds : sin A = sin Ecos v + ( os Bjeosdcosu or 
sin A = Asin? ty, EK (cot. */, Beosv—eosd eos u) 
For the deorsumduction holds: sin D= sin Ecos À iS ae E\cosweosvor 
sin D= 2sin?*/, E(cot.'/, Hcosa— cos cosy) 
In these formulae A=abduction, D=deorsumduction, B= eaxcur- 
sion, whilst 2, u and rv represent the angles of the axis of motion 
with the z-, y- and c-axis. If the axis of motion lies in the plane 
of Listine (frontal level) the formulae become much less complicate 
namely : 
sin A= sin HK cos v 
sin D = sin Ecos 4, 
In this case # indicates at the same time the angle between line 
of vision and y-axis. If the axis of motion does not lie in the plane 
of Listinc, then the angle between line of vision and y-axis (/H) 
is expressed in the formula: 
cos H = sin? woos E+ cos*u or 
sin |, A =sinwsin */, 2. 
An isolated function of the m. obliq. sup. is inconceivable in a 
normal eye. Such an isolated function is only: possible with definite 
paralysis of the muscles of the eye. 
We must however call the attention to the fact, that with a para- 
lysis of the muscles of the eye the center of rotation is likely to change 
its place somewhat, as the constant location of the center of motion 
is a function, partly of the tensions of the tissues, and the resistan- 
ces of the tissues partly of the distribution of the tensions over the 
