THE SENSE OF SIGHT. 



157 



It is attached anteriorly to the inner surface of the sclerotic and cornea, 

 and posteriorly to the choroid coat opposite the ciliary processes. At the 

 anterior border of the radiating fibres and internally are found bundles of 

 circular muscular fibres, constituting the annular muscle of Miiller. The 

 ciliary muscle thus consists of two sets of fibres, a radiating and circular, 

 both of which are concerned in effecting a change in the convexity of the 

 lens in the accommodation of the eye to near vision. 



The Retina forms the internal coat of the eye. In the fresh state it is a 

 delicate transparent membrane of a pink color, but after death soon becomes 



FIG. 20. 



d - 



SCLEROTIC COAT REMOVED TO SHOW THE CHOROID, CILIARY MUSCLE AND NERVES. 



a. Sclerotic coat. b. Veins of the choroid. c. Ciliary nerves, d. Veins of the choroid. 

 e. Ciliary muscle, f. Iris. From Holden's Anatomy. 



opaque; it extends forward almost to the ciliary processes, where it termi- 

 nates in an indented border, the ora serrata. In the posterior part of the 

 retina at a point corresponding to the axis of vision is a yellow spot, the 

 macula lutea, which is somewhat oval in shape and tinged with yellow 

 pigment. It presents in its centre a depression, the fovea centralis, corres- 

 ponding to a decrease in thickness of the retina ; about one-tenth of an 

 inch to the inner side of the macula is the point of entrance of the optic 

 nerve. The arleria centralis retince pierces the optic nerve near the 

 sclerotic, runs forward in its substance and is distributed in the retina as far 

 forward as the ciliary processes. 



