134 J. PARSONS SCHAEFFER 



The second frontal furrow or pit after first developing into a 

 cellula ethmoidalis anterior continued to extend its boundaries 

 until it became topographically the sinus frontalis. It should 

 be noted that the duct of the sinus frontalis (ductus nasofron- 

 talis) is in the position of the embryonic second frontal furrow 

 or pit and that it is in the same axis as the infundibulum eth- 

 moidale and the hiatus semilunaris/ but not in direct continuity 

 with them. The sinus frontalis in this instance (fig. 6) com- 

 municates, therefore, with the recessus frontalis directly via the 

 ductus nasofrontalis. On the other hand, the infundibulum 

 ethmoidale ends blindly as a cellula ethmoidalis anterior (in- 

 fundibular cell) lateral to the recessus frontalis and the ductus 

 nasofrontalis. 



The anatomy represented in figure 6 is that found in a cer- 

 tain number of adult specimens, and is illustrative of one of the 

 anatomic types of the region. It should be noted that the in- 

 fundibulum ethmoidale is not directly continuous with the ductus 

 nasofrontalis, but that it bears an intimate and important rela- 

 tion to it. The relation is, in a sense, a contiguous and not a 

 continuous one. Drainage from the sinus frontalis would find its 

 way partly into the meatus nasi medius directly. An explora- 

 tory probe passed towards the frontal region via the infundibulum 

 ethmoidale would, of course, find its way into the ventral, blind 

 end of the latter and not into the sinus frontalis. To probe the 

 sinus frontalis in this case it would be necessary to pass through 

 the proximal ostium of the ductus nasofrontalis located in the 

 recessus frontalis. 



It is interesting and instructive to compare the embryologic 

 anatomy of the recessus frontalis illustrated in figure 1 with the 

 adult anatomy illustrated in figure 6. In the former the third 

 frontal furrow and the infundibulum ethmoidale are in the 

 same axis; in the latter, the second frontal furrow (now the 

 nasofrontal duct) is in the same axis as the infundibulum eth- 



1 Tlie term hiatus semilunaris should be applied to the lunate cleft which 

 establishes a communication between the infundibulum ethmoidale and the 

 meatus nasi medius, i.e., the slit between the free border of the processus unci- 

 natus and the bulla ethmoidalis. 



