36 THE EYE. 



the pigmentary layer is more clearly visible through it in the dead condition, giving 

 rise to an appearance as of a hole through the tunic. About 3 mm. inside the 

 yellow spot and about 1 mm. below the level of a horizontal line through the 

 posterior pole of the eyeball is a pale, round disc, poms options (figs. 46 and 47), 



EPITHELIUM^ 

 CONJUNCTIV/Ejj 



MUSCULUS 

 CIUARIS^ 



ARTERIA / 



CENTRALIS / 



RETIN/E /'/' 



r.-DURAt. SHEATH 



Fig. 45. RIGHT ADULT HUMAN EYE, DIVIDED HORIZONTALLY THROUGH THE MIDDLE. 

 (Magnified five times.) 



The line a b passes through the equator, x y through the visual axis of the eye. 



where the optic nerve pierces the retina and expands to form its inner layer. The 

 circumference of the disc is slightly elevated to form an eminence (colliculus nervi 

 opt id) (fig. 45) and in its centre, which often shows a well-marked depression, is 

 the point from which the vessels of the retina branch. 



