4 WILLIAM H. F. ADDISON AND HAROLD W. HOW 



structures of the lids continue to grow and to approximate until 

 the epithelium forms only a narrow band between the two lids. 

 As the two lids come together, it appears that the greater part 

 of the intervening epithelium is pressed aside. This is to be 

 seen as little irregular groups of epithelial cells attached to the 

 junction epithelium, either on the outer side or on the con- 

 junctival side (figs. 4 and 6). In figure 4 the epithelium between 

 the two lids measures 63^. Here the basal row of epithelium on 

 each lid margin is again columnar, while the intervening cells 

 are rounded and vesicular. The length of the band of epithelium 

 measured in the direction of the line of fusion is about 90ac. 



At this period, as before, the vibrissae buds of the face are 

 distinct, but now for the first time other hair buds are beginning 

 to develop in the skin, and occasionally one is found on the sur- 

 face of the lid itself. The muscle fibers in the lid are plainly to 

 be seen and the mesenchyme is distinctly more condensed on 

 the conjunctival side of the lid. 



Nineteen-day fetus 



At this stage the proportions of the band of epithelial cells 

 forming the junction have already become somewhat altered 

 (fig. 6). By the growth of the opposing mesenchymatous struc- 

 tures the junction epithelium now measures only about 50/x 

 from the basement membrane of one lid to that of the other. 

 While in the direction from the conjunctival surface to the outer 

 surface it has doubled in extent and measures about 180/x. 

 This junction epithelium consists of a basal layer of columnar 

 cells resting on the mesenchymatous portion of each lid, and 

 three or four irregularly disposed rows of pale-staining, rounded, 

 vesicular cells intervening. Both on the inner and outer sides 

 of the junction epithelium are seen clumps of epithelial cells 

 (fig. 6, ep) which have been pressed aside by the opposing growth 

 of the two lids. 



Twenty-day fetus 



The cells of the epithelium on the outer surface of the lids are 

 now arranged in three strata. The basal layer is columnar. 



