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



layers of the mature retina. After this time there is continued 

 growth of the eyeball which alters the proportions of the several 

 layers, but one can at least say that the retina at the time of 

 disjunction of the lids is histologically mature. 



The chief single factor in the separation of the lids is the 

 keratinization process which appears in the surface cells of the 

 epidermal side of the junction epithelium, as in epidermal cells 

 everywhere (figs. 7 and 8). For a time the process does not 

 manifest itself more actively here than elsewhere (fig. 9), but at 

 a certain period, which we may associate with a definite stage in 

 the maturing of the hair follicles of the skin, this process con- 

 tinues to progress inward in the midhne of the junction epithe- 

 lium (figs. 10 to 13), until it reaches the conjunctival side. 



The mechanism of cornification in the junction epitheHum is 

 probably comparable to that taking place elsewhere over the 

 integument. The history of the junction epithelium is, however, 

 somewhat different from that of the ordinary epidermis, inas- 

 much as for some days after the lids fuse it becomes progressively 

 thinner in the interpalpebral direction, then has a stationary 

 thickness until the seventh day, and finally gradually increases. 

 It is only when the last stage is reached that keratinization pro- 

 ceeds rapidly in the epidermal groove. This accounts for the 

 delay in the process within the junction epithelium as com- 

 pared with the general surface epidermis. Connected with 

 these circumstances, causing delay, is also the fact that the 

 margins of the lids are in a younger developmental condition 

 than the remainder of the Hds. At least, one may infer this 

 from the fact young stages of hair folHcles are still seen there 

 when the adjoining follicles of lids and general skin show well- 

 developed shafts. The increase in thickness in the junction 

 epithelium goes slowly, probably because of the concurrent 

 expansion of the marginal area of the lids. There is rapid 

 proliferation of the epithelium, but many of the new-formed 

 cells are necessary to keep up with the expanding marginal 

 surface of the lid, and are distributed laterally. This is the con- 

 dition up to six or seven days, by which time most of the hair 

 follicles of the adjoining part of the lid are mature and their 



