256 ANATOMY, PHYSIOLOGY, &C. 



constituting the integuments of the eye, and within 

 which the other essential parts are contained. These 

 are in the form of two cups, applied to each other at 

 the margin, and hence the eye-ball approaches a 

 globular form. The cup, which is situated with the 

 convexity inwards, is termed the sclerotic coat. It 

 determines the shape of the eye, and is perforated 

 posteriorly for the passage of the optic nerve. 



The central aperture, or transparent point on the 

 retina, has been discovered in the eye of no other 

 animals besides man, except in the quadrumana 

 (apes, &c.), the axes of whose eyes are parallel to 

 each other, and are like the human. 



In the eyes of the cat, the choroides reflect, in- 

 stead of absorbing, the rays of light. 



Magnifiers of the Eye. 



The eye is found to be composed of several na- 

 tural magnifiers, which make a picture on a mem- 

 brane at the back of it, and from this membrane a 

 nerve goes to the brain, conveying the impressions of 

 a picture, by means of which we become conscious 

 of its existence. 



The different natural magnifiers of the eye are 

 combined on the same principle as the compound 

 magnifiers of a telescope ; the eye, in fact, consist- 

 ing of different liquids which act naturally in cor- 

 recting refraction and other imperfections. 



The Hair. 



The hair of the human head is always dark at the 

 base, and continues so during the change to grey. 



The peculiar colour of the hair is given to it by 

 an oily matter. 



Chyle. 



Chyle is a close approximation to blood ; it is de- 



