SPECIAL SENSES. 



THE EYE. 



THE eye is the organ of sight. It is placed in the 

 orbital cavity, which protects it from injury. The eye- 

 ball is movable in all directions by the muscles attached 



FIG. 178. DIAGRAM OF A HORIZONTAL SECTION THROUGH THE HUMAN EYE. 



1, cornea ; 2, sclerotic : 3, choroid ; 4, ciliary processes ; 5, suspensory ligament of lens ; 

 6, so-called posterior chamber between the iris and the lens : 7, iris : 8, optic nerve : 8', en- 

 trance of central a'tery of retina; 8", central depression of retina, or yellow spot; 9, 

 anterior limit of retina ; 10, hyaline membrane; 11, aqueous chamber; 12, crystalline lens; 

 13, vitreous humor; 14, circular venous sinus which lies around the cornea; a a, antero- 

 posterior, and b b, transverse axes of bulb. 



to it, and is capable of a wide range of vision. It is 

 imbedded in a quantity of loose fat, from which it is 

 separated by a flattened serous sac, the capsule of 

 Tenon. 



The eyeball consists of the segments of two 

 spheres, a smaller anterior, constituting one-sixth, and 



(413) 



