THE SINUS FRONTALIS 145 



attached, the following were the five ways in which develop- 

 ment of the sinus frontalis occurred and the percentage of 

 each variety: 



1. By the extension of one of the cellulae front ales in 41 

 per cent, of cases. Such development is shown in Figs. 

 21, 23, 36, 41, 45, 47, and 51. The development of the 

 cellulae frontales, the variations in their number, and the 

 irregularities in the degree of prominence attained by the 

 conchse frontales were considered on pages 46 and 53. 



2. By the extension of the recessus conchalis no cellulae 

 frontales being demonstrable in 18.4 per cent, of cases. 

 Figs. 38, 43, and 48 show this type of development. In this 

 class of cases the conchse frontales have either failed to de- 

 velop or else were represented by such slight folds that they 

 were completely resorbed during the expansion of the recessus 

 conchalis. 



3. By the extension of a cellula ethmoidalis anterior 

 having its origin from the suprabullar furrow, in 1 per cent, 

 of cases. Such development is distinctly shown in Fig. 33. 



4. By the direct extension of the infundibulum ethmoidale, 

 in 15.6 per cent, of cases. (See Figs. 35 and 56.) 



5. By the extension of one of the cellulae infundibulares 

 in 24 per cent, of cases. Variations in this type of origin 

 are shown in Figs. 28, 39, 49, and 55. 



Summarizing the above classification of origins, we find 

 that sinus frontales developing by the first three methods 

 a total of 60.4 per cent, of the cases in this series communi- 

 cate with the meatus medius without communicating with 

 the infundibulum ethmoidale. Sinuses which develop by 

 the fourth and fifth methods, however, a total of 39.6 per 

 cent, of the cases in this series, communicate with the 

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