XII 



PHYLUM CHORD AT A 



355 



various directions by a number of muscles inserted into it. 

 On the side of the eyeball directed towards the light the 

 opaque sclerotic is replaced by a transparent membrane 

 the cornea (c.), which forms a window through which the 

 rays of light enter the eye. Within the sclerotic is a more 

 delicate pigmented layer the choroid (ch.\ Towards the 



e.c 



e.cj 



Civ 



Scl' 



FIG. 206.- -Diagrammatic horizontal section of the eye of Man. c. cornea; ch. 

 choroid (dotted); C.P. ciliary processes ; e.c. epithelium of cornea, continuous 

 with e. cj. conjunctiva ; f. c. yellow spot ; /. iris ; L. lens ; O.N. optic nerve ; 

 os. ora serrata, the line at which the retina proper ends; o.r, optic axis; 

 /. c. /?, anterior non-visual portion of retina ; P.E. pigmented epithelium (black) ; 

 R. retina; sp. L suspensory ligament; Scl. sclerotic; V.H. vitreous humour. 

 (From Foster and Shore's Physiology.} 



cornea the choroid passes into a circular pigmented 

 diaphragm the iris (/.), the opening of which is known 

 as the pupil. Through the pupil, the size of which is 

 capable of being increased or diminished, the light is 

 admitted into the interior of the eye. The sensitive part 

 of the eye the part on which the image produced by the 



A A 2 



