2O6 



ELEMENTARY PHYSIOLOGY 



raised into a number of ridges which constitute the ciliary pro- 

 cesses. 



The iris (Lat. a window) is the circular curtain, seen through 

 the cornea, which gives the colour to the eye. Its outer border 

 is continuous with the choroid coat, which, like the sclerotic, does 



Fig. 190. View of the Human Eye, divided horizontally through 

 the middle. 



i, conjunctiva ; 2, cornea ; 3, sclerotic ; 4, sheath of the optic nerve ; 5, choroid ; 

 6, ciliary processes ; 7, iris ; 8, pupil ; 9, retina ; 10, anterior limit of the retina ; 

 xi, crystalline lens; 12, suspensory ligament; 13, ciliary muscle; 14, aqueous 

 chamber; 15, vitreous chamber; 16, yellow spot ; 17, blind spot. 



not extend over the front of the ball. It is perforated in its 

 centre by a circular aperture called the pupil. The iris is a con- 

 tractile membrane. It is provided with unstriped muscular fibres, 

 some of which are arranged in a ring around the pupil, while the 

 others are radiating. When the circular fibres contract, the pupil 

 is made smaller ; when the radiating fibres contract the pupil is 



