604 APPENDIX 



Anterior Chamber. This is the space between the iris and cornea 

 and is filled with the aqueous humor. Through the pupil will be 

 seen the crystalline lens. The space between the iris and the lens 

 is called the posterior chamber and also contains aqueous humor. 



The Crystalline Lens and the Coats of the Eye. Make a median 

 section through the remaining part of the eye. The lens in cross 

 section, the cut edges of three coats, and a transparent jelly-like 

 mass, the vitreous humor, will be seen. 



The coats from within outward are : 



1. The retina, a very thin, white membrane, covering the inside 

 of the eye, except the anterior part. The retina is a continuation 

 of the optic nerve. At its posterior part where the nerve enters 

 may be seen a small area, the blind spot, from which several minute 

 blood-vessels radiate. 



2. The choroid coat, which is the middle tunic of the eye, is pig- 

 men ted,, and firmer than the retina. This coat appears black or 

 blue in the specimen, and is continued into the ciliary body and 

 the iris, the former supporting and controlling the shape of the 

 lens in accommodation. 



3. The outer coat is the solera, the anterior part of which is 

 transparent and called the cornea. It is thick and fibrous, giving 

 strength and form to the eye. It is white in appearance, is pierced 

 by the optic nerve at the back, and gives attachment to the muscles 

 on its outer surface. 



Lens. Separate the halves of the lens from the vitreous humor 

 in which they are embedded. Note that the lens is composed of 

 concentric layers, like an onion. It is surrounded by a capsule. 

 Note that the anterior surface is flatter than the posterior. 



REFRACTION IN THE EYE 



The eye is an instrument for producing upon a sensitive surface, 

 the retina, images of objects in space. The production of an image 

 requires a device for focussing. In the eye the cornea and lens 

 together make up the focussing apparatus. The eye is so con- 

 structed that rays of light coming from points more than 18 feet 

 away are focussed naturally upon the retina. 



The fundamental fact of vision, the formation of images by 

 lenses can be demonstrated with the aid of a double convex lens, 



