EYEBALL 



in an antero-posterior direction into a medial and a lateral half. A third 

 should be Divided horizontally and a portion of the vitreous body should be 

 removed (Fig. 251). When the sections are made, they should be placed 

 under water in a cork-lined tray, and preserved for reference as the study 

 of the eyeball is proceeded with. 



General Structure of the Eyeball. The eyeball consists 

 of three concentrically arranged coats enclosing a cavity in 

 which three refracting media are placed. 



The tunics are: (i) an external fibrous envelope com- 

 posed of a posterior opaque part, called the sclera, and an 



Pupil 



Anterior chamber ; L ens 

 Iris 'i ' i 



Posterior chamber 



Ciliary body 

 Corona ciliaris 



Cornea 

 ,' Zonula ciliaris 



Venous sinus of sclera 

 JL Conjunctiva 



Chorioid 



Vitreous body' 



- Hyaloid canal 



Central fovea 

 Optic nerve 



FIG. 251. Diagrammatic section of Eyeball. 



anterior clear transparent portion called the cornea ; (2) an 

 intermediate vascular envelope known as the uveal tract, in 

 which three subdivisions are recognised, viz., a posterior part 

 called the chorioid, an anterior portion termed the iris, which 

 lies posterior to the cornea, and an intermediate ciliary body ; 

 (3) the nervous internal tunic or retina, in which the fibres 

 of the optic nerve spread out. 



The refracting media are: (i) posterior to the cornea a 

 watery fluid, called the aqueous humour, contained in a 

 space partially subdivided by the iris into the two chambers 

 of the eye; (2) the crystalline lens posterior to the posterior 



