THE CAT 245 



nective tissue, the anterior portion of which is the transparent 

 cornea. The boundary between the cornea and the sclerotic is 

 marked by a prominent white ridge. 



With sharp scissors cut two large openings in the side of the 

 eyeball, opposite each other, and study the interior of the eye. 

 Carefully remove the other eye from the orbit and cut it in two 

 by an equatorial incision. Note behind the pupil the large, trans- 

 parent crystalline lens ; do not disturb it. The layer just within 

 the sclerotic is the choroid coat, the anterior portion of which is 

 the iris. The choroid coat contains the blood vessels of the eye. 

 Within the white ridge of the sclerotic just mentioned the choroid 

 is thickened by the presence of a large number of radiating ridges, 

 which form the ciliary body. This structure forms thus a broad 

 black ridge around the inner surface of the eye. Extending inward 

 from this ridge is a delicate membrane called the suspensory liga- 

 ment ; this is continuous with the transparent capsule in which the 

 lens is suspended. Delicate muscle fibers are present in the ciliary 

 body, by which the position of the crystalline lens is changed 

 when the focus of the eye is adjusted. A layer of cells, called the 

 tapetum lucidum, which has a metallic sheen and reflects the light, 

 is present in the choroid coat, in the region of the optic nerve; it 

 causes the cat's eyes to shine in the dark. 



The inner coat of the eye is the retina. It is a soft, delicate 

 membrane which will often be found separated from the choroid ; 

 it is the sensitive portion of the eye, and is in direct connection 

 with the optic nerve. The point where the nerve pierces the 

 sclerotic and choroid coats and joins the retina is shown by a small 

 round spot, called the blind spot because the sensitive elements 

 of the retina are here absent. Anteriorly the retina gradually 

 becomes thinner, and ends on the inner surface of the iris. Just 

 behind the ciliary body it forms a serrated ridge called the 

 ora serrata. 



The crystalline lens is a large, double-convex, transparent body 

 situated immediately behind the iris ; its convexity is greater 

 on the anterior than on the posterior side. It is suspended in a 

 delicate capsule, which is attached to the ciliary body by the sus- 

 pensory ligament. 



