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



ridges indicating the beginning of the Hds, but in the succeeding 

 twenty-four hours the Hds have grown over the eyeball and 

 have fused by their epithelial margins. 



As the lids approach each other the epithelium at the margin 

 of each lid grows actively in advance of the mesenchymatous 

 portion. 



By measurements of the conjoined epithelium, three stages 

 are observed during the period of attachment: 1) increase in 

 length of fusion; 2) stationary attachment, and, 3) gradual 

 separation. The first stage lasts until four days after birth, the 

 second until the sixth or seventh day, and the third until final 

 disjunction at fourteen to seventeen days. 



The period from union to disjunction of the lids may be cor- 

 related with a fairly definite period of development of the skin 

 and hair. Thus the time of formation of the lids is slightly in 

 advance of the first appearance of hair follicles of the ordinary 

 small hairs. Then the lids remain completely fused until after 

 the arrival of the skin at the stage of cornification of its super- 

 ficial epithelial layers, the formation of the hair shafts, and their 

 appearance above the surface of the skin (about seven days after 

 birth). Finally, the stage of gradual separation is associated 

 with the maturing of the hair follicles, which have originated 

 from the junction epithelium. 



The chief factor in the sphtting of the junction epitheUum 

 during stage 3 is the process of keratinization, which continues 

 inward from the surface epidermal cells of the raphe until it 

 reaches the conjunctival side of the junction epithelium. Dur- 

 ing stage 3 the interpalpebral dimension of this junction epithe- 

 lium gradually increases, and it is apparently this increase in the 

 mass of epithelial cells which brings the cells of the midhneof 

 the raphe farther and farther away from the source of nourish- 

 ment, and so favors the progress of the keratinization process 

 within them. The inception of increase in the interpalpebral 

 dimension is correlated in time with the arrival of the skin of 

 the lid at its mature condition, while the margins of the lid are 

 still in a younger developmental condition. By the time the 

 folhcles of the latter have developed hair shafts, the keratiniza- 



