14 J. PARSONS SCHAEFFER 



By the beginning of the third month (in some cases before) 

 the lacrimal-duct cords have developed sufficiently to come in 

 contact with the epithelium on the free borders of the eyelids. 

 We will, however, find that the ducts are as yet in places solid 

 cords. Portions of the mother cord, especially the portion that 

 is destined to become a portion of the lacrimal sac, are active in 

 lumen formation at this time. The fundus of the lacrimal sac 

 apparently develops as a sprout from the mother cord. The 

 nasal end of the mother cord has not developed sufficiently to 

 come in contact with the mucous membrane of the inferior 

 nasal meatus. It is, however, not far removed, and in a later- 

 stage embryo it will be found coalesced with the nasal mucous 

 membrane. Lumen formation at the point of coalescence of the 

 mother cord with the nasal mucous membrane is delayed approxi- 

 mately until 'term' (figs. 22, 23 and 24). 



Frontal sections of embryos aged approximately one hundred 

 days will show that the nasal end of the mother cord of cells has 

 developed to the nasal mucous membrane and has coalesced with 

 it. Both lacrimal-duct cords have grown to the free borders of 

 the eyelids and have coalesced with the epithelium at these points. 

 The mother cord of cells, or the portion destined to become the 

 greater portions of the lacrimal sac and the nasolacrimal duct, 

 has by this time established irregular lumina at various points. 

 The latter are best developed at the ocular end of the primary 

 cord and towards the nasal end of the cord. The lacrimal-duct 

 cords have also established lumina at various points, especially 

 in the regions of the knees, or what will later become the ampullae 

 of the lacrimal ducts. 



In figs. 14, 15 and 16 (embryo aged one hundred and seven days) 

 is well illustrated the irregular manner in which the cords of epi- 



Figs. 14, 15, and 16 Photomicrographs of frontal sections through the naso- 

 lacrimal passages of a human embryo aged one hundred and seven days. Note 

 both lacrimal ducts (fig. 14) in contact and fused with the epidermis in the region 

 of the free borders of the eyelids. The lacrimal ducts have not yet established 

 lumina in the regions of the eyelids (fig. 14). The remaining portions of the ducts 

 are more or less patent throughout. Note the irregularity of lumen formation in 

 the nasolacrimal duct (fig. 16). sld = superior lacrimal duct; ild = inferior lacri- 

 mal duct; eld = common lacrimal duel ; Is = lacrimal sac; nld = nasolacrimal duct. 

 X 10.5. 



