, NASOFRONTAL REGION IN MAN 127 



now partly ossificil, are at this time sufficiently developed to 

 throw the nasal mucosa into relief. Between the folds are 

 found pits or furrows, the positive growth or outpouching of 

 which aids materially in making more prominent the folds. It 

 is appropriate to speak of the latter as accessory or hidden 

 frontal folds or conchae and the pits as frontal furrows, of the 

 meatus nasi medius. As mentioned above, there is no con- 

 stancy in the degree of differentiation and development of the 

 frontal folds and furrows. The number varies from a complete 

 absence to four or five. In some instances, therefore, the re- 

 cessus frontalis remains a simple blind outgrowth from the meatus 

 nasi medius without configuration of its lateral wall (fig. 5). 



The processus uncinatus and the folds composing the bulla eth- 

 moidalis likewise should be considered as accessory conchae of 

 the meatus nasi medius (analogues and homologues of the 

 frontal conchae), and the infundibulum ethmoidale and the supra- 

 bullar furrow as accessory meatuses or furrows of the meatus 

 nasi medius (analogues and homologues of the frontal furrows). 



The accessory furrows of the meatus nasi medius are fore- 

 runners of certain of the sinus paranasales, i.e., the sinus frontalis, 

 the sinus maxillaris, and the anterior group of cellulae eth- 

 moidales (by anterior group is meant all those ethmoidal cells 

 which communicate with the nasal fossa caudal to the attached 

 border of the concha nasalis media, including both the ante- 

 rior and middle group according to another classification) . 



The frontal furrows or pits early evaginate and form certain 

 of the anterior group of cellulae ethmoidales or cellulae fron- 

 tales. Semi-coronal sections through the recessus frontalis show 

 these early cells. When these cells are followed in serial sec- 

 tions toward the recessus frontalis, they are shown to be ex- 

 tensions or outpouchings of the frontal furrows and in com- 

 munication with the recessus frontalis. Some of the cellulae 

 ethmoidales having their genesis in frontal pits remained di- 

 minutive and ethmoidal in topography, while others grow to 

 considerable size and often develop beyond the confines of the 

 ethmoidal bone. 



