676 Jacob Parsons Schaeffer. 



resorption of surrounding bone, this taking place pari passu with 

 the growth of the face. 



For a further consideration of the sinus maxillaris the reader 

 is referred to a previous paper bearing directly upon this cavity. 



The sinus frontalis 



The point from which the sinus frontalis develops is somewhat 

 variable. Like the sinus maxillaris it develops from a preformed 

 cavity or space. In a previous paragraph mention was made of the 

 frontal recess, and of the folds and furrows which configure its 

 lateral wall. The recess and the furrows especially concern us 

 in connection with the development of the sinus frontalis. It 

 will be recalled that the number of furrows is variable, and that 

 the infundibulum ethmoidale bears inconstant relations to these 

 furrows (figs. 3S to 43). At term, or even somewhat earlier, the 

 furrows have already pouched at their superior ends towards the 

 frontal region, thus forming early anterior ethmoidal cells. 

 Frontal and horizontal sections will, therefore, if made at appro- 

 priate planes, show cross-sections of cavities instead of furrows 

 (compare figs. 36, 44, and 32). The frontal recess is at this time 

 also quite roomy and is more or less variable in its extent (figs. 

 36 and 41). 



As KilHan has properly pointed out, the frontal sinus may 

 develop from one or more anterior ethmoid cells, from an eth- 

 moid cell and the frontal recess, or by direct extension of the 

 whole frontal recess. At birth it can hardly be said from what 

 point the frontal sinus will ultimately develop into the adult 

 cavity. According to my studies the frontal sinus may also in 

 exceptional cases develop from the superior and ventral end of 

 the infundibulum ethmoidale, i.e., the infundibulum ethmoidale 

 continuing its development superiorly and ventrally, lateral to 

 the frontal recess and frontal furrows, and then expanding into 

 the sinus frontalis. In the vast majority of cases, however, the 

 infundibulum ethmoidale has absolutely nothing to do with the 

 development of the frontal sinus. 



