190 J. PARSONS SCHAEFFER 



adult ostium: If at the most cephalic point of the meatus nasi 

 inferior, the ' penetration' of the nasal mucous membrane is more 

 or less direct, and the large, unguarded, open-mouthed ostium 

 of the adult would very likely result (compare figs. 6 and 12). 

 On the other hand, if the strand of cells strikes the lateral wall of 

 the meatus nasi inferior obliquely, the resulting ostium is likely 

 to be slit-like and more or less guarded by a plica lacrimalis (com- 

 pare figs. 5 and 10 with fig. 13). 



The area of coalescence between the strand of epidermal cells — 

 the anlage of the nasolacrimal passages — and the nasal mucous 

 membrane is, at times, quite extensive (fig. 14). In the process of 

 lumen formation, in such cases, it is reasonable to believe that 

 several ostia, communicating between the ductus nasolacrimalis 

 and the meatus nasi inferior, may be formed. I believe that these 

 extensive areas of coalescence account for most cases of dupli- 

 cation of the ostium nasolacrimale. Intervening bridges of mu- 

 cous membrane would, of course, remain as the division planes 

 between the several ostia (figs. 8 and 14 should be compared). 



In the development of the nasolacrimal passages we frequently 

 see bud-like projections extending from the main strand of epi- 

 dermal cells (fig. 15). These buds are frequently seen near the 

 meatus nasi inferior. It is reasonable to believe, in some instances, 

 that several of these nasal sprouts establish communication with 

 the meatus nasi inferior. Such a development would account 

 for a duplication of the ostium of the ductus nasolacrimalis. It 

 would also account for the rarer condition in which the several 

 ostia open into independent, short canals which in turn open into 

 the ductus nasolacrimalis. Usually however the bud-like pro- 

 jections from the main strand of cells do not develop sufficiently 

 to establish coalescence with the nasal mucous membrane, but 

 end blindly. The latter would account for the very common 

 diverticula from the adult ductus nasolacrimalis. 5 Doubtless 

 many of these buds disappear entirely. It is well known that we 

 may also have a duplication of one or both of the ductus lacrimales. 

 This duplication must be explained along similar lines. 



6 J. Parsons Sehaeffer, Variations in the anatomy of the nasolacrimal passages. 

 Annals of Surgery, August, 1911. 



