324 



The outermost bundles of muscular fibre run in meridional 

 lines. They stream backwards from the cornea and lose them- 

 selves on the outer surface of the ciliary body and choroid. 

 These fibres are connected in front with the middle of the 

 three divisions of the posterior elastic lamina of the cornea 

 (the inner division of this lamina spans the margin of the 

 anterior chamber and forms the pillar of the iris, and the 

 outer division passes backwards and outwards to the sclerotic 

 behind the space known as the circulus venosus, or Schlemm's 

 canal) . 



The shortening of these meridional bundles of muscular 

 fibre will tend to approximate their corneal and choroidal 

 attachments, and if we regard the corneal one as the more 

 fixed point, a view which best harmonizes with the anato- 

 mical facts, the contraction of these bundles tends to draw 

 the choroid forwards and tighten it upon its contents. Ac- 

 cording to this view, the ciliary muscle (as regards its radial 

 bundles) is a tensor of the choroid, as Briicke named it. 



Actions of the Lens and Ciliary Muscle. — Let us next see 

 what light these anatomical data throw on the process of ac- 

 commodation. You will recollect that in accommodation for a 

 nearer object, the lens as a whole does not shift its place, but its 

 anterior surface becomes notably more convex, and the convexity 

 of its posterior surface is very slightly increased. With this 

 alteration of its figure, the axis is lengthened and the transverse 

 diameter shortened. The pupillary region of the iris approaches 

 the cornea, and the circumference of the iris retreats from it. 



The lens with its capsule is elastic but without contractile 

 irritability ; its role is passive. When the suspensory ligament 

 is tight it must exert traction on both surfaces of the lens 

 (chiefly on the front, by reason of the greater stoutness of the 

 fibres and of their attachment to the lens, advancing rather 

 farther from the edge of the lens) tending to compress the 

 lens in the direction of its axis, and to flatten it — the shape 

 of the lens in looking at a distant object, which is a passive 

 act, not requiring accommodation. 



When the radial or longitudinal bundles of the ciliary 

 muscle contract, and the distance between their extreme 

 points of attachment is lessened, the previously tense sus- 

 pensory ligament is relaxed and the lens, no longer compressed 

 by it, becomes more convex by nature of its own elasticity. 

 If, at the same time, the circular bundles of the muscle were 

 to shorten, this would tend to contract the circle of the ciliary 

 processes, by which the suspensory ligament would be still 

 more slackened ; I doubt, however, whether they can act as 

 a compressor of the edge of the lens. The ciliary muscle 



