140 J. PARSONS SCHAEFFER 



rather common occurrence), the sinus frontahs and the sinus 

 maxillaris would from a practical viewpoint be in direct communi- 

 cation. It should be recalled that the sinus maxillaris is geneti- 

 cally an outgrowth from the floor of the infundibulum ethmoi- 

 dale. The initial area of the outgrowth varies considerably in 

 extent, thus accounting for the varied size of the adult ostium 

 maxillare.^ 



The sinus frontalis is occasionally present unilaterally or bi- 

 laterally in duplicate or in triplicate. In these cases each sinus 

 frontalis is absolutely independent of others and possesses an 

 individual ostium frontale. The condition of duplicity or tri- 

 plicity of the sinus frontalis is readily explained when one re- 

 calls the potentiality of development referred to in previous 

 paragraphs (figs. 1 to 5). In figures 9 and 10 are represented 

 dissections of adult nasofrontal regions in which two frontal pits 

 (early ventral or anterior cellulae ethmoidales) developed 

 sufficiently far to be topographically sinus frontales. Dupli- 

 cate sinus frontales are either side by side in the sagittal plane 

 (fig. 10) or are ventral and dorsal in relation, in the coronal plane 

 (fig. 9). Intermediate relations are, of course, encountered. In 

 figure 11 the first and second frontal pits developed into sinus 

 frontales; in figure 10 the second and third. In both instances 

 the sinuses communicate independently with the recessus fron- 

 talis of the meatus nasi medius. At times when the sinus 

 frontalis exists in duplicate (or triplicate) one sinus may en- 

 croach bullous-like on the other. The name bulla frontahs was, 

 however, applied by Turner to infundibular cells which encroach 

 upon the dorso-caudal boundary of the sinus frontalis. 



The ductus nasofrontalis is a very variable channel. One en- 

 counters very many specimens in which no true duct is present. 



- "In my series of 90 cases it (the ostium maxillare) has a great range of di- 

 mensions; varying from 1 to 20 mm. in length and from 1 to 6 mm. in width. In 

 some instances where the ostimii has reached considerable size, it almost entirely 

 replaces the caudo-lateral wall of the infundibulum ethmoidale, thus forming a 

 long, slit-like communication l)etween the sinus maxillaris and the infundibulum 

 ethmoidale." J. P. Schaeffer, Am. Jour. Anat., vol. 10, 1910, p. 351. 



