COORDINATION IN ANIMALS 



201 



visual elements (RODS and CONES) of the eye, while the outer 

 supplies the PIGMENTED LAYER. The nerve cells of the retina 

 develop fibers which proceed to the brain through the path 



FIG. 112. The Vertebrate eye (human). A, vertical section of the eye in situ. 

 B, horizontal section to show relation of optic nerve to fovea centralis through which 

 the optical axis passes, a, eyelash; b, lid; c, bony orbit; d, superior rectus, one of the 

 six muscles which revolve the eyeball; e, muscle to upper lid; /, optic nerve (bundles 

 of fibers cut obliquely); g, inferior rectus muscle of eyeball; h, anterior chamber filled 

 with aqueous humor; i, pupil, opening to posterior chamber, also filled with aqueous 

 humor, between iris and lens; j, conjunctiva, a transparent membrane, continuous with 

 the lining of the eyelid; k, cornea; I, iris; ra, lens; n, suspensory ligament of lens; 

 o, retina; p, choroid coat; q, sclerotic coat; r, muscles to ligament suspending lens; 

 s, vitreous chamber containing vitreous humor; t, point of entrance of optic nerve 

 ('blind spot'); u, fatty connective tissue; x, fovea centralis at posterior end of axis 

 of eyeball. 



occupied by the optic stalk and so give rise to the OPTIC 



NERVE. 



To the optic cup and lens, the former indirectly and the 

 latter directly of ectodermal origin, other portions largely of 

 mesodermal origin are added e. g., the CORNEA, CHOROID 



