CHAPTEE XIV. 



DEVELOPMENT OF THE STRUCTURES CONCERNED 

 IN THE SENSE OF SIGHT. 



The structures concerned in the sense of sight are : 



(1) The Eyeball and the Optic Nerve. 



(2) The Eyelids and Lachrymal Apparatus. 



(3) The Orbit, the Muscles, Nerves, and Vessels contained 

 it. 



(4) The Nerve Centres and Tracts. 



The Eyeball. — The condition of the eye in the third week of 

 etal life is shown diagrammatically in Fig. 141. The three 



fprebrain 



optic uesicle 

 epiblast 

 neuroblast 

 mesobfast 

 mid-brain 



hind-brain 



Fig. 141.— Diagram of the Elements which form the Eyeball. 



ements which unite to form the eyeball are as yet separate, 

 tiey are : 



(1) Epiblast, which forms (a) the epithelium of the cornea, (b) 

 ie lens, and probably (e) the rods and cones of the retina. 



