338 ANATOMY AND PHYSIOLOGY 



lightly upon it. It is held in place by delicate fibers which form 

 a suspensory ligament; this is normally a little tense, exerting a 

 slight but constant pressure upon the eyeball. 



The ciliary muscle is in the interior of the eyeball, around the junction of 

 the choroid and iris, thus lying a little farther forward than the border of the 

 lens. By its action it draws the suspensory ligament forward, releasing the 

 lens from pressure; thus it modifies the shape of the lens; by this arrange- 

 ment the eye is able to accommodate itself to the different distances of sur- 

 rounding objects. This is the process of accommodation. To "paralyze the 

 accommodation" is to make the ciliary muscle powerless, so that the eye 

 cannot try to see near objects, as it always does unconsciously, in its normal 

 condition. Atropin will do this. 



Clinical notes. Inflammation of the iris, or iritis, may cause adhesions to 



Macula H-r^X jy<v '"3 Retinal vessel 3 



FIG. 216. THE RETINA AS SEEN WITH THE AJD OF THE OPHTHALMOSCOPE. (Morris.') 



the lens unless the margin of the pupil be drawn away. This is the reason for 

 the use of atropin, which weakens the circular fibers while it stimulates the 

 straight ones, or, in other words, dilates the pupil. 



Cataract is a thickening of the lens which makes it opaque and gives it a 

 milky appearance. The remedy is excision or removal of the lens, after which 

 a convex lens of glass in front of the eye gives a good degree of vision. A 

 cataract is in an eye, not over it, and must be taken out, not o$. 



Aqueous humor and chambers of the eye. The space be- 

 tween the cornea and the lens is partially divided by the iris into 

 two portions the anterior and posterior chambers of the eye. 

 They contain a thin clear fluid, called the aqueous humor, which 

 floats the iris and aids in preserving the shape of the cornea 

 (Fig. 214). 



Note. The rays of light which fall upon the retina must first 

 pass through the media (or structures which direct their course) in 

 the following order: the cornea, aqueous humor, crystalline lens, and 



