CHAP, in.] SIGHT. 949 



side, its mid-point lying not far from the vertical meridian of the 

 eyeball. 



The inferior oblique muscle arises from the front of the floor 

 of the orbit on the nasal side ; it is directed at first backwards 

 to the temporal side, underneath the inferior rectus, between 

 that and the floor of the orbit, and then passing upwards and 

 backwards is inserted into the sclerotic underneath the external 



LEFT EYE 



FROM TEMPORAL SIDE FROM ABOVE 



Sup.R 



r _ Sup.O. 

 inf.O 



Inf.R EXt ' R lnf.0 



FIG. 159. THE LEFT EYE SEEN FROM A, THE TEMPORAL SIDE. B, FROM 



ABOVE, SHEWING THE INSERTIONS OF THE OCULAR MUSCLES. (JeSSOp.) 



rectus in the hind temporal part of the ball. The line of inser- 

 tion (Fig. 159) is also an oblique one like that of the superior 

 oblique but it is placed somewhat farther past it ; its hind end lies 

 not far from the entrance of the optic nerve and it runs thence 

 forwards and downwards. 



593. The manner in which these muscles are thus sever*- 

 ally attached to the eyeball suggests that in contracting they 

 would move the eyeball in the following ways. Taking changes 

 in the direction of the visual axis as indicating the nature of 

 each movement we should expect that the superior rectus would 

 turn the visual axis upwards, the inferior rectus downwards, 

 the external rectus outwards towards the temporal side, and the 

 internal rectus inwards towards the nasal side. The inferior 

 oblique, its insertion being on the hind and lateral part of the 

 eyeball, and the direction of the muscle being downwards, 

 would in contracting turn the visual axis upwards, while the 

 superior oblique having a somewhat similar insertion but acting 

 in an opposite direction would turn the visual axis downwards. 

 Both muscles however in thus raising or lowering the visual 

 axis would, owing to the oblique direction of their insertions 

 at the same time, turn it to the temporal side ; the movement 

 as the names of the muscles suggest, would be an oblique 

 one. 



