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PHYSIOLOGY. 



Uses. By reason of its vascularity the choroid is destined to 

 nourish the all-important and underlying retina. By reason of its 

 elasticity and contained musculature the choroid maintains intra- 

 ocular pressure. The pigment of the choroid is believed to serve a 

 dioptric purpose: that of absorbing the superfluous rays of light 

 which pass through the eyeball on their way to the retina. Their 

 absorption prevents dazzling and interference with vision. 



Fig. 328. Dissection of the Zonula. (After SCHULTZE.) 

 1, Lens. 2, Cut surface of iris. 3, Ciliary processes. 4, Choroid. 5, Zonula. 



Ciliary Muscle. The fibers of this muscle can .be divided into 

 three parts: (1) The strongest layer is nearest the sclerotic. It is 

 composed of a thick layer of fibers having a meridional direction, 

 which extend backwards into the choroid. (2) The second part of 

 the muscle contains fibers which are less intimately connected with 

 each other. Their direction deviates more, and they radiate towards 

 the center of the ocular globe. These fibers terminate near the pos- 

 terior surface of the ciliary body. (3) The third part of the ciliary 

 muscle is represented by the ring-muscle of H. Miiller, and is much 





