DEVELOPMENT OF EYELIDS OF ALBINO IL\T 19 



days only cornified epithelium connects the two lids in the region 

 midway between the inner and outer canthi. 



The measurements of the junction epithelium in the inter- 

 palpebral direction at the various stages are in a general way 

 the reverse of those in the conjunctiva-skin direction. Imme- 

 diately after fusion at eighteen days, the interpalpebral meas- 

 urements is 63m, and as the mesenchymatous portions of the lids 

 press together, this becomes less, so that at two days after birth 

 it is only 30 to 38//. It remains about the same until the seventh 

 day, and then gradually increases, so that at ten days it is 73^, 

 and at twelve days 90m . As the two lids continue to separate 

 through the cornification of the epithelium in the midhne of the 

 junction epithehum, half of the epithelium belongs to each Hd, 

 constituting its surface layer. 



Thus during the period of attachment of the lids, there are 

 three stages, as indicated by the measurements of the junction 

 epithelium: 1) Increase in length of line of fusion; 2) stationary 

 attachment; 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 ensues at fourteen to 

 seventeen days. 



The period of attachment of the hds is related in time with 

 especially two other developmental processes, the maturing a) 

 of the skin and b) of the retina. 



Being specialized integumentary structures, the lids in their 

 developmental history follow the same general course as the 

 skin. Hair folhcles are developed both from the epithehum of 

 the skin and from the junction epithehum. By following the 

 development of the hair folhcles which grow from the latter 

 situation, one gets a sure guide to the time when the separation 

 process is going on. For, as has been shown already, by the 

 time the hair shafts form in these folhcles, the sphtting of the 

 junction epithelium has proceeded far enough for the hair shafts 

 to grow out directly through the epidermis of the margin of the 

 lid. It is found that new hair folhcles continue to arise from 

 the conjoined epithelium for several days after most of the 

 follicles have begun in adjoining parts of lid and head. As a 



THE AMERICAN JOUBNAL OF ANATOMY, VOL. 23, NO. 1 



