THE EMBRYOLOGY OF THE EYE. 65 



At first the epithelium of the lid consists of 

 a single layer. The epithelium of the outer 

 surface and of the margin becomes several 

 cells deep, and that of the inner surface two 

 or three cells deep (Fig. 9). The basal stratum 

 of columnar cells stains deeply and soon be- 

 comes pigmented (Fig. 20). Very early we find 

 the external epithelium dipping in in places 

 to form hair follicles (Fig. 8). After the lids 

 unite similar indippings at the margins form 

 the follicles for the cilia. Just behind these, 

 larger solid epithelial processes push a consid- 

 erable distance into the lids, and later break 

 down in the centre to form tubes, which give 

 off short processes, and become Meibomian 

 glands (Fig. 20). 



At an early stage we find long fusiform cells 

 developing into clear muscle-fibres (Fig. 9), 

 which appear first near the orbital margin of 

 the lids and much later near the free margin. 

 These muscle-fibres are finally collected into 

 bundles separated by loose connective tissue, 

 and form the orbicularis muscle. 



