22 J. PARSONS SCHAEFFER 



of the ostia are doubtless due to the angle at which the original 

 cord of cells meets the nasal mucous membrane. The position of 

 contact also makes a difference. If the ostium is at the highest 

 point of the inferior meatus, i.e., just caudal to the attachment 

 of the inferior nasal concha to the lateral nasal wall, the opening 

 of the nasolacrimal duct is usually a large, wide, open-mouthed 

 ostium, unguarded by folds of mucous membrane (fig. 28). 

 If, on the other hand, the ostium is farther caudal on the lateral 

 wall it is usually slit-like and more or less guarded by folds of 

 mucous membrane (figs. 28). 



Even at term the embryo presents very irregular nasolac- 

 rimal ducts (fig. 24). After biHh the walls of the ducts become 

 more and more regular In the adult we very frequently find 

 large diverticula from the nasolacrimal duct, and these added to 

 other irregularities give us at times extremely irregular lumina 

 (figs. 30 and 31). On the other hand we find adult ducts in 

 which the lumina are very simple and regular (fig. 29). The 

 lumina of the adult lacrimal ducts (lachrymal canaliculi) are gen- 

 erally more or less irregular. 



SUMMARY 



1. The strand of thickened epithelium — the anlage of the naso- 

 lacrimal passages — along the floor of the rudimentary naso-optic 

 fissure becomes entirely separated from the surface, and for some 

 time is wholly surrounded by mesenchymal tissue. 



2. The strand or cord of epithelial cells thus isolated from the 

 surface is for some time without a lumen. 



3. From the mother cord of cells both lacrimal ducts and the 

 nasal end of the nasolacrimal duct grow as sprouts. The cephalic 

 portion of the lacrimal sac also grows as a sprout from the mother 

 cord. 



4 ( 1 onsiderable variation occurs in the development of the 

 lacrimal ducts, i.e., as to number, time, and degree of develop- 

 ment. 



5. The lumina of the several portions of the nasolacrimal pas- 

 sages are established in an irregular manner. The ocular end 



