114 CONSCIOUS NERVOUS OPERATIONS 



of the clioroid coat. It consists of plain muscle fibers, 

 whose nervous supply comes from the third cranial nerve. 

 The ciliary muscle is attached to the ciliary processes, and 

 these to a membrane called the suspensory ligament. 

 This ligament is secured also to the circumference of the 

 lens in such a way that when the eye is at rest it is in a 

 state of tension, which causes it to pull upon and slightly 

 flatten the lens. This keeps the eye at the focus neces- 

 sary for seeing clearly objects at a distance of perhaps 

 twenty or twenty-five feet. When the eye is directed to 

 a nearer object, the fibers of the ciliary muscle contract, 

 thereby drawing forward the ciliary processes, and thus 

 lessening the tension on the suspensory ligament, and the 

 elasticity of the lens causes it to push forward, or become 

 more convex on its front surface. This shortens the focal 

 distance, that is, causes the rays of light to converge more 

 rapidly. The cornea alone is capable of forming distinct 

 images, and the chief function of the crystalline lens seems 

 to be that of accommodation. 



153. Function of the Iris. The iris (Fig. 63) is an adjust- 

 able curtain, designed, by narrowing the pupil, to cut off 

 a portion of the light which might render the image con- 

 fused, and to prevent too strong a light from entering the 

 interior of the eye. This change in the size of the pupil 

 is effected by the contraction and relaxation of its mus- 

 cular tissue, under control of the ciliary nerves. 



154. Inversion of Images (Figs. 60 and 68). As in a 

 camera, so in the eye the image formed is inverted. The 

 rays of light cross in being brought to a focus, so that 

 the picture of a man, a house, or a tree on the retina is 

 upside down, and also much smaller than the object itself. 

 The reason why we do not see objects inverted and re- 

 duced in size is because it is not the picture on the retina 



