558 



MANUAL OF PHYSIOLOGY. 



face of the cornea which hold it in position ; the fibres of the 

 ciliary muscle, running under the ciliary processes, radiate from 

 the margin of the cornea toward the choroid, to which they are 

 attached. In a modified form, known as the iris, this vascular 

 and pigmented coat of the eye leaves the sclerotic, and hangs 

 freely in a fluid so as to be recognized through the clear cornea 



FIG. 215. 



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'. Entrance of central 

 artery of the retina; 8". Central depression of retina or yellow spot; 9. Anterior limit 

 of the retina; 10. Hyaloid membrane; 11. Aqueous chamber; 12. Crystalline lens; 13. 

 Vitreous humor ; 14. Circular venous sinus which lies around the cornea ; a a, antero- 

 posterior, and, 66, transverse axis of bulb. 



as a colored circular curtain, attached to the inside of the pe- 

 riphery of the cornea, and having a central deficiency, which looks 

 black, and is familiarly known as the pupil. This pupil is merely 

 an opening in the iris, which allows the rays of light to pass into 

 the interior of the eyeball. 



Besides supplying nutrition to the non-vascular central parts 



