16 J. PARSONS SCHAEFFER 



thelial cells establish lumina. Note that the lacrimal ducts are 

 more or less patent throughout, save at the free borders of the 

 eyelids where solid cords still persist. The horizontal and verti- 

 cal portions of the lacrimal ducts are well shown (fig. 14). The 

 lacrimal sac (fig. 15) is well advanced but the remainder of the 

 nasolacrimal duct is not wholly patent. Even at this early stage 

 there is some evidence of beginning diverticula from the naso- 

 lacrimal duct (fig. 16). The connection with the inferior nasal 

 meatus is, of course, not yet established (fig. 16). 



According to my studies, the ocular end of the mother cord 

 is the first to establish a lumen. The horizontal portions of the 

 lacrimal ducts become patent before the vertical portions (figs. 

 14 and 17). The last parts of the vertical portions of the lacri- 

 mal ducts to become patent are the junction points between the 

 lacrimal-duct cords and the epithelium of the free borders of the 

 eyelids (fig. 17). The nasal end of the mother cord establishes 

 a lumen before the middle portion of the cord (figs. 19 and 20). 

 The middle portion remains solid, according to my series of 

 embryos, for some time longer (fig. 19). The last portion of the 

 nasolacrimal passages to become patent is at the point of coal- 

 escence between the nasal sprout of the mother cord and the 

 nasal mucous membrane. This is usually deferred, as stated 

 before, until 'term' or even later (fig. 24). 



In the adult we find varying positions on the lateral wall of 

 the inferior nasal meatus for the ostium of the nasolacrimal 

 duct. The ostium also varies as to shape, and it is occasionally 

 duplicated. Rarely we find a triplicity of the ostium. 



The position of the ostium, i.e., whether at the highest point 

 of the inferior nasal meatus, or at varying distances below the 

 above point on the lateral nasal wall, depends, of course, largely 

 upon the original point of coalescence of the mother cord of cells 

 with the nasal mucous membrane (fig. 28). At times the area of 

 coalescence between the cord of cells and the nasal mucous mem- 

 brane is rather extensive (fig. 21). In such cases, due to the irre- 

 gular mode of lumen formation, two or more ostia may readily 

 be formed (instead of the usual single ostium) with a bridge of 

 intervening tissue remaining permanently. The different shapes 



