458 



vessels. Towards the vitreous they are limited by a denser layer of 

 cells which form a compact border which is not connected with the 

 retina. The margins of the cleft turn in more and more and the 

 pigment passes over into the inner layer for a short distance (Fig. 3). 



(abnormal) 



Figs. 



Fig. 3. Fig. 4. 



3 and 4. Corresponding areas in the equatorial region ; the lips of the ab- 



normal separated and filled with mesoderm and pecten in the normal. 



Very close to the region of the opticus, for the first time, the 

 two layers of the retina become continuous (Fig. 5) hitherto the two 

 lips of the cleft were separated by a wide space bridged over by the 

 compact layer of cells, before mentioned, which are on a level with 

 the inner layer of the retina (Fig. 3). When the two layers become 

 continuous then the pigment layer ceases long before reaching the 

 outstretched lips of the retinal lamellae (Fig. 5). In the extreme ends 



(abnormal) 



Fig. 5 shows how the layers ot the retina have coalesced in the region of the 

 optic nerve. 



of the lips in the neighborhood of the optic nerve, can be seen nerve 

 fibres in spite of the great irregularity of the course of the growth 

 of this eye. The most striking feature in the abnormal eye is the 

 absence of the pecten. The pecten normally is formed by a plate of 

 mesoderm passing through the cleft and then the two margins of the 



