looking downward the m. obliquus superior is neither entirely in- 
significant, though, according to Zora, the moment of the m. rectus 
inferior is three times larger for looking downward. For the 
abduction, on the contrary, the m. obliquus superior has only a 
very slight signification, and in cooperation with other abducent 
forces it can, at best, support the abduction somewhat. 
Does the knowledge we have obtained enable us also to estimate 
in some degree the maximal excursion of the eye by contraction of 
the m. obliquus superior? By excursion we must understand the 
angle that the eve makes, moving round a constant axis of motion, 
in this case through contraction of the m. obliquus superior. 
VOLKMANN supposed that he could give an affirmative answer 
to this question, by admitting that the maximal excursion was 
reached, when the point of insertion coincided with the tangential 
point. Re adds to this, that witb further contraction of the muscle, 
no rotation would take place, but a removal of the center of rotation. 
The maximum found by him for the average eye amounted to 
26° 55’. 
A few objections might be raised against this conclusion: 
1. Beside the couple that moves the eye, there exists always a 
force that tries to remove the center of rotation. As soon however 
as the point of insertion has reached the tangentialpoint, the force 
that tries to remove the center of rotation will become proportion- 
ally greater. 
2. The calculated maxima of excursion of the 4 mm. recti do 
not correspond with the size of the field of vision. 
Calculated maxima Size of the field of vision according to 
of excursion accord- 
ing to VOLKMANN | VoLKMANN SCHUURMANN AUBERT KiisTER HERING NAGEL, 
M. rect. ext. 60°43’ 38° 42° 38° 43° 43° 50° abduction 
M. rect. int. 29°31’ 42° 45° 44° 45° 45° 50° jabduction 
M. rect. sup. 41938’| 35° | 34° 30° | 33° | 20° | 45° | upward 
| 
M. rect. inf. 41°43’ 50° 51° 57° | 44° 60° | 45° | down- 
| | ward 
3. The maximal excursion for the two obliqui calculated accord- 
ing to VOLKMANN would amount for the m. oblig. sup. to: 26°55’, 
»/ 
for the m. obliq. inf. to: 78°18’. This relation is not probable. 
4. If we calculate from the maximal excursion and the length 
of the muscle-fibres (likewise measured by VorKMANN) the maximal 
abbreviation of the different muscles of the eye, then those would 
