33* 



ELEMENTS OP PHYSIOLOGY 



612. The Conjunctiva. The eye is apparently set in a 

 slit in the skin of the face, but this is not really the case. 

 The skin of the eyelids turns inward over their edges and 

 becomes a thin, transparent, and exceedingly sensitive 

 mucous membrane, called the conjunctiva. It is, like 

 other mucous membranes, composed of epithelial cells. 

 The conjunctiva goes back under the lid and over half 

 the eyeball itself to the other lid, so that the eye is really 

 behind the skin. When the eye is directed very much 



to one side, the con- 

 junctiva is sometimes 

 seen lying in wrinkles. 

 The veins which we 

 think we see in the 

 white wall of the eye- 

 ball when the eye is 

 "blood-shot" are usu- 

 ally in the conjunc- 

 tiva, which is so trans- 

 parent that we do not 

 easily see it unless its 

 vessels are swollen. 



613. The Eyeball 



(Fig. 214) is a globular chamber filled with transparent 

 fluids. By studying Fig. 214 you will see that its wall 

 is made of three layers, or coats. The sclerotic coat in 

 the "white of the eye" is the tough white outer coat 

 of connective tissue. It preserves the shape of the 

 eye and serves for the attachment of the muscles. This 

 coat is pierced in only one place, and that is for the 

 entrance of the optic nerve. It is continuous over the 

 front of the eye, where it becomes transparent, and is 

 called the cornea. You can see the cornea bulging out 

 in the front of a classmate's eye if you look at the eye 

 from the side. The middle coat, the coat just within the 



etinji 

 horoid 

 'erotic coat 



FiG. 214. The Anatomy of the Eye. 



