THE EMBRYOLOGY OF THE EYE. 29 



might suppose the entire vitreous to be divided 

 into lamellae by the striations, and this mistake 

 would seem to have been often made. Further 

 than these striations along the vessels I be- 

 lieve there are no structural elements in the 

 vitreous causinor a stratification which can be 

 demonstrated with the microscope. 



d. Zonula. The anatomy of the zonula is 

 still imperfectly understood, and its develop- 

 ment is still more uncertain. Recent writers 

 (Czermak, Berger, Topolanski, and others) 

 have devoted considerable study to its normal 

 structure, but there are many points on which 

 there is not general agreement. 



At the time when the ciliary processes are 

 being formed the retinal vessels stop at the 

 place where the retina gradually thins down 

 into the pars ciliaris (Fig. 13). The limitans 

 interna, however, continues over the ciliary 

 body, and from this time on grows gradually 

 thicker, forming a distinct homogeneous mem- 

 brane on the pars ciliaris. The superficial 

 portion of the vitreous anteriorly has a fibrillar 



