122 



TOPOGRAPHICAL ANATOMY OF THE 



this tunic. The rest of the very delicate membrane consists of nervous 

 and connective tissue. It is in the nervous layers of the retina that the 

 fibres of the optic nerve have their origin, a circumstance that accounts 

 for the gradual increase in the thickness of the membrane as its point 

 of connection with the nerve is approached. That part of the, retina 

 that contains nervous elements is distinguished by the name pars 

 optica retinae. At an indistinct line, the ora ^ serrata, close to the 

 edge of the ciliary body, the nerve elements cease and the retina 

 suddenly becomes thinner. From this line the membrane is continued 

 over the ciliary body as the pars ciliaris retinae, and thence on to the 

 posterior surface of the iris as the pars iridica retinae. 



Sclera. 



M. rectus superior.^ 



-Ora serrata. 



Conjunctiva.. 

 Ciliary muscle 



Venous sinus.. 

 Angle of the iris 



Cornea 



Anterior chamber. 



Capsule of lens. 



Iris. 



Granula iridis.- 



Ciliary processes. 

 Suspensory ligament of lens. 



Posterior chamber. 



— 1\ — — .— ": Crystalline lens. 



Fig. 52. — Section throitgh the ciliary body and iris of the eye. 



When the retina is viewed from within, the entrance of the optic nerve 

 is distinguishable as a well-defined, pale, oval area, the optic papilla 

 (papilla optica), below and lateral to the posterior pole of the eyeball. 

 The transverse diameter of the papilla is the greater, being about 

 6-7 mm., while the vertical diameter is 4-5 mm. The central part of 



1 Ora (from os, a mouth) [L.], a border, edge, boundary, &c. Serratus [L.], 

 toothed like the edge of a saw, notched at the edge. 



