8 WILLIAM H. F. ADDISON AND HAROLD TV. HOW 



pronounced than before and both the stratum granulosum and 

 the stratum corneum are a little thicker at that point than in 

 the adjacent skin epidermis. 



Three-day rat 



Although sections show that hair follicles are now a prom- 

 inent feature of the skin of the lid and that many of them con- 

 tain definite hair shafts, very few of the latter have yet appeared 

 above the surface of ths skin. Coincident with the differentia- 

 tion of the hair shaft within the basal part of the follicle there is 

 a keratinization process going on within the outer part of the 

 follicle where it is continuous with the surface epithelium. This 

 process results in the formation of a canal or outlet to the fol- 

 licles, through which the developing hair shaft will grow. At 

 this period the process is only partly completed in many foUicles. 



The most evident change in the junction epithelium is the 

 slight deepening of the outer groove. Its measurements are 

 250m in the conjunctival-epidermal length and about 40^ at its 

 narrowest part between the two lids. The hair-follicles at the 

 outer angle of the margin of the lids are in several stages of 

 development. The longest, measuring 200 to 250ai, show a 

 distinct papilla at the base and a growing shaft within the root 

 sheaths. Near the mouth of the follicles are small oval out- 

 buddings of epithehal cells to form sebaceous glands. Where 

 these longest follicles are connected with the outer part of the 

 junction epithelium, the cells in the line of future progression 

 of the hair shaft have become more cornified and their nuclei 

 are no longer apparent. These cells show the situation of the 

 mouth of the follicle, and the stratum granulosum of the epider- 

 mis is seen to be dipping in to form the boundary of the mouth 

 of the follicle. It is thus easy to be seen that the formation of 

 the mouths of these follicles has a distinct effect upon the outer 

 part of the junction epithelium in the way of tunnels being 

 formed through it in preparation for the hair shafts growing out. 



The tarsal glands now measure 175/^ in length, whereas at 

 birth they measured only 70/jl. 



