DEVELOPMENT OF EYELIDS OF ALBINO RAT 7 



Inspection of figure 8 shows that there is a slight indentation 

 of the outer surface of the junction epitheUum, a feature which 

 becomes progressively more marked at later stages. In the skin 

 are more hair follicles than before. These are of various ages, 

 some just beginning, others already differentiated and contain- 

 ing a hair shaft (fig. 8, h). But none of the hair shafts can be 

 traced beyond the epidermis. The vibrissae on adjoining parts 

 of the head are already well-developed structures, projecting as 

 much as 3 mm. beyond the surface of the skin. The hair follicles 

 of the outer angle of the lid, however, are mostly in a young 

 condition, and only in the largest ones can be seen a developing 

 shaft. The longest follicles measure 175^. The tarsal glands 

 at the inner angle are still short, solid, flask-shaped epithelial 

 buds, measuring about 70yu in length. The voluntary muscle 

 fibers in the lids are growing in size and now have their nuclei 

 peripherally placed. 



Two-day rat 



Considerable advance is seen in the structures within the lids 

 as compared with the condition in the newborn. The hair fol- 

 licles are more numerous and the older ones have increased 

 both in diameter and in length. Many of the largest follicles 

 contain a hair shaft, and an occasional one of these begins to 

 protrude through the epidermal surface. Those in the lids 

 nearest the junction are, however, not so far advanced as those 

 farther away from the junction, and while some of the former 

 show beginning differentiation of the hair shaft, they are not yet 

 fully formed. Midway between the follicles at the external 

 angle of the lid, and the tarsal glands at the internal angle are 

 seen very small buds of hair follicles which are just beginning to 

 develop from the junction epithelium. 



The junction epithelium now measures 250m in length from 

 the conjunctival surface to the outer epidermal surface, as com- 

 pared with ISOfjL at birth. The diameter of the junction epithe- 

 lium at its narrowest point is about 30^. The indentation on 

 the outer surface of the junction epithelium is slightly more 



