544 PHYSIOLOGY 



this pressure the membranes which confine the fluids of the eyeball are dis- 

 tended, i.e. pressed outwards, and this pressure keeps the bases of the ciliary 

 processes pressed against the choroid coat and thus enables them to withstand 

 the pull exerted by the tense suspensory ligament. 



The pull exerted by the suspensory ligament affects mainly the tough an- 

 terior surface of the lens capsule and so has a constant flattening effect on the 

 anterior surface of the lens. This may be proved by measuring the curvature 

 of the lens in a recently excised eye, and then removing the lens altogether 

 from the eyeball and measuring the curvatures of its surfaces again. It 



Cornea 



Sinus venosus 



Conjunctiva 



Corpus Zpnula 

 ciliare clliaris 



Retina 



FIG. 271 . Section through anterior part of eyeball to show mode of 

 suspension of lens. (After MEEKEL and KALLITJS.) 



will be found that, as soon as the lens is free from its attachments in the 

 eyeball, the curvature of its anterior surface is increased. The change 

 therefore in the lens, which is responsible for the alterations in its refractive 

 power determining accommodation, may be effected by any means \\Lich 

 will relax the suspensory ligament, such, for instance, as approximation of 

 the ciliary processes to the margin of the lens. This movement of the ciliary 

 processes is effected by the ciliary muscle. The attachments of this muscle 

 are shown in Fig. 271 . It forms a circle of unstriated muscle fibres, triangular 

 in cross-section, and extending round the whole circumference of the eyeball. 

 The fibres of the muscle are divided into three groups : 



(a) The meridional fibres, which run from the corneo- sclerotic junction 

 backwards and outwards to be attached to the anterior part of the choroid 

 coat behind the ciliary processes. 



(b) The radial fibres, which pass from the margins of the canal of Schlemm, 





