586 



PHYSIOLOGY 



a movement of the pupil will be associated with rotation of the eyeball. 

 The first of these conditions is practically fulfilled by the external and 

 internal rectus muscles, as is shown in the diagram (Fig. 299). These muscles 

 by their contraction will move the pupil directly outwards or directly inwards. 

 The axis of rotation in the diagram would run vertically through the eyeball. 

 The other four muscles produce movements with axes of rotation which are 

 not at right angles to the visual axis. The rectus superior, for instance, 

 produces rotation round the axis joining r.sup. and r.inf., and will therefore 

 produce movement of the eyeball upwards and inwards with a certain amount 

 of rotation of the eyeball on its antero-posterior diameter. The rectus 

 inferior in the same way moves the eyeball downwards and inwards with 



i.in 



r.ext. r.sup. r.inC 

 r.vtf, 



FIG. 299. Diagram to show points 

 of attachment and liens of action 

 of extrinsic ocular muscles. 



rinf 



FIG. 300. Diagram to show direction in 

 which pupil will move under the action 

 of the various ocular muscles. 



rotation. The obliquus superior moves the eyeball downwards and out- 

 wards, and the obliquus inferior upwards and outwards, in both cases with 

 some rotation on its antero-posterior axis (Fig. 300). The only movements 

 of the eyeball therefore which can be carried out by the action of one muscle, 

 or by the reciprocal action of a pair of muscles, are the movements outwards 

 and inwards, which are involved in the common actions of convergence of the 

 visual axes and conjugate deviation of both eyeballs. Movements upwards 

 or downwards will require the co-operation of at least two muscles. In order 

 to direct the gaze upwards a contraction of the superior rectus which moves 

 the eyeball upwards and inwards must be associated with a contraction of the 

 inferior oblique muscle which rotates the eyeball upwards and outwards. In 

 the same way the inferior rectus muscle will be associated with the superior 

 oblique. 



As we have seen, four out of six muscles when acting singly cause rotation 

 of the eyeball on its antero-posterior axis. The question arises whether 



