300 



STUDIES IN PHYSIOLOGY 



General Form of the Eye. If the six muscles be severed 

 near their attachment to the eyeball, the eye is still held in 

 place by the large optic nerve, which enters the eyeball from 

 behind. When removed from its socket, each eye appears 

 to be spherical in its general shape ; but a closer examina- 

 tion shows that the exposed region bulges outward some- 

 what from the rest of the eyeball. 



FIG. 136. 



A = muscles of right eyeball viewed from above. 



B = muscles of left eyeball viewed from outer side. 

 Ch = crossing of optic nerves. 



11= second or optic nerves. 

 ///= third nerve to eye-muscles. 

 ER, Inf. Ob, Inf.R, S.Ob, SR = muscles that move the eyeballs. 



Coats of the Eye. In a section of the wall of the eyeball 

 one can make out three coats. The outer is composed of 

 tough connective tissue. The portion of this coat which 

 incloses the back part of the eyeball is called the sde-rot'ic 

 (Greek skleros = hard). The white of the eye, which one 

 can see beneath the eyelids, is the front region of this scle- 

 rotic coat. The bulging part of the eye, to which we have 

 already referred, is covered by a portion of the outer coat, 

 called the cor'ne-a (Latin corneus = horny). Through this 

 hard but transparent layer one can see the colored i'ris and 

 the black pu'pil. 



