THE EMBRYOLOGY OF THE EYE, 47 



tinct fold where the ciHary body is to be 

 formed. 



The inner layer of the vesicle-wall becomes 

 thinner in its anterior portion (Figs. 8 and 9), 

 until, like the outer layer, it comes to consist 

 of a single stratum of cells — the pars ciliaris 

 retinae (Fig. 11). Farther back the inner 

 layer is thicker and passes imperceptibly over 

 into the rudimentary retina. Anteriorly the 

 single stratum of cells becomes pigmented in 

 the portion that is to form the posterior layer 

 of the iris, the pigmentation ceasing at the 

 head of the ciliary body (Fig. 11). In speci- 

 mens from the grown pig, bleached by Collins' ' 

 method, the posterior layer of the iris with the 

 pigment removed consists of cells entirely 

 similar to those of the pars ciliaris, the only 

 difference being that the layer on the iris does 

 not have a smooth posterior surface, but forms 

 a succession of short curves. 



Some time after the development of the 

 equatorial fold to form the ciliary body, meridi- 



1 Trans. Ophthal. Soc. Unit. Kingdom, vol. xi. 



