XnTE. 501* 



NOTE TO PAGE 180. 



At the page indicated, the action of the straight muscles of the eye-ball has been 

 shortly described, but no notice is taken of that of the oblique muscles. The omission 

 was deemed advisable, from the difficulty of giving within a short space an intelli- 

 gible account of a matter still involved in uncertainty; but the attention of the 

 Editors having been drawn to it as a defect which it was desirable to remedy, they 

 have endeavoured to do so in the present note. 



The motions of the eye-ball take place round three axes, viz., a transverse, a vertical, 

 and an antero-postehor. Those round the first two axes are effected more imme- 

 diately by the straight muscles, which have also the power by the successive or con- 

 current contraction of different ones among them to direct the pupil to all the points 

 of space within the cone by which the movements of direction are limited. The 

 movements of rotation on an antero-posterior axis are no doubt effected chiefly by 

 the oblique muscles ; but it is still doubtful to what extent and in what circumstances 

 these movements occur. 



By the experiment of Bonders, viz., that of turning the head downwards to the side 

 after an ocular spectrum of a bright vertical line has been fixed in the eyes, and which 

 it is easy to repeat with the same result, it is ascertained that the eyes turn accurately 

 with the head, and are not balanced in the vertical position by the rotary action of 

 the oblique muscles, as was supposed by Hueck and others. The rotation of the eyes 

 by the oblique muscles must therefore have some other object. 



When the optic axis is directed straight forwards, the simple action of the superior 

 oblique muscle (as ascertained by experiment on the dead subject) is to direct the 

 pupil with some degree of rotation downwards and outwards; that of the inferior 

 oblique to produce a similar movement in an upward and outward direction ; and no 

 doubt both muscles acting in concert on one eye, while the optic axis is still straight 

 forward or is somewhat everted, may produce a horizontal outward movement of the 

 pupil. But if on the other hand the eye is turned forcibly inwards, it is conceivable 

 that, as then the points of insertion of the oblique muscles will be brought further 

 forward, these muscles may along with other movements give an inward direction to 

 the pupil. 



The most important actions of the oblique muscles probably take place in com- 

 bination with one or more of the straight muscles. Careful observations ap- 

 pear to have proved that the recti muscles are incapable of altering materially the 

 form of the eye-ball, or of diminishing its distance from the back of the orbit ; and it 

 is equally certain that the oblique muscles have little or no effect as antagonists in 

 drawing forward the eye-ball. It would appear, however, that while the external and 

 internal recti muscles act exactly in the horizontal plane between them, so as not to 

 produce any upward or downward direction along with their horizontal movements, 

 the superior and inferior recti, from the obliquity of the line in which they proceed 

 forwards towards their insertion, have both a tendency to direct the eye somewhat 

 inwards. It seems very probable, according to the views stated in the papers referred 

 to below, that the inward direction produced by the superior or inferior rectus may 

 be corrected by the combination of the action of different oblique muscles with that 

 of one or other of the recti muscles; i. e., the inferior oblique with the superior 

 rectuB, and the superior oblique with the inferior rectus. In a similar manner the 

 oblique muscles may also counterbalance an increased inward direction given by the 

 internal rectus, and increase an outward direction given by the external rectus. 



On the whole, it seems probable that the oblique muscles have the effect of main- 

 taining accurately the parallelism of the two eyes by balancing the action of the 

 several sets of straight muscles. 



See for an account of this subject and its application to the study of different forms 

 of paralysis of the muscles of the eye, a paper by Dr. John S. Wells in the Ophthalmic 

 Hospital Eeports, &c., vol. ii. 1859-60, p. 44; and a paper by Von Graefe on the 

 Physiology and Pathology of the Oblique Muscles of the Eye in the Archiv fur 

 Ophthalmologie, vol. i. part i. p. 1. 



