144 J. PARSONS SCHAEFFER 



drainage from the sinus frontalis would, of course, readily find 

 its way into the sinus maxillaris. The infundibulum in these 

 cases acts in every sense as a gutter of communication between 

 the sinus frontalis and the sinus maxillaris. The same is true 

 in a large number of cases in which the relations are intimate but 

 not contiriuous between the ventral extremit}^ of the infundibu- 

 lum ethmoidale and the derivatives of the recessus frontalis. 

 The sinus maxillaris in turn becomes a reservoir for drainage 

 from the sinus frontalis and certain cellulae ethmoidales anterior 

 (some infundibular and others frontal in position). If in those 

 cases in which the sinus frontalis or its duct is directly continu- 

 ous with the ventral extremity of the infundibulum ethmoidale 

 (fig. 8) the ostium maxillai'e should occupy a goodly or greater 

 portion of the floor of the infundibulum ethmoidale (a condition 

 encountered), the sinus frontalis and the cellulae infundibulares 

 would, from a practical viewpoint, be in direct communication 

 with the sinus maxillaris. This close relationship is, however, 

 secondary and one must not infer that the frontal and maxillary 

 sinuses and the infundibular cells arise from the same point. 



CONCLUSIONS 



The materials studied for this paper seem to justify the fol- 

 lowing conclusions : 



1. The sinus frontalis is in the vast majority of cases a deriva- 

 tive (a) of the recessus frontalis directly, (b) of one or more 

 of the cellulae ethmoidales anterior which have their genesis 

 in frontal pits, or (c) of both, when present in duplicate or 

 triplicate. 



2. The sinus frontalis appears occasionally to arise from the 

 ventral extremity of the infundibulum ethmoidale. This rela- 

 tionship, however, is in some instances secondary owing to de- 

 velopment. It is ciuestionable whether the sinus frontalis ever 

 develops from the suprabullar pit or furrow. 



3. The ductus nasofrontalis (or the sinus frontalis directly in 

 the absence of a ductus) and the infundibulum ethmoidale are 

 in the vast majoritA^ of instances, discontinuous channels in the 



