126 



PARSONS SCHAEFFER 



from. The recessus frontalis in turn is the anlage of tlie sinus 

 frontahs and certain of the anterior group of cellulae ethmoi- 

 dales (also called cellulae frontales by Killian, Onodi and others). 

 As early as the end of the third or beginning of the fourth 

 month of embryologic life, one sees evidence of a beginning ex- 

 tension of the meatus nasi medius in a ventrocephalic direction. 

 This early extension is the anlage of the recessus frontalis and 

 is, strictly speaking, the first step in the formation of the sinus 

 frontalis and certain of the anterior group of cellulae ethmoi- 

 dals. For some time the lateral wall of the recessus frontalis is 



, Frmfal fi/rro?vs 



CoJicha 7iffS.?//ed (riitj, 

 B'oe. v7/f:/n(/fus 



Fig. 1 From a term fetus. The recessus frontalis is exposed for study by the 

 removal of the operculatino; concha nasalis media. Note the frontal furrows 

 and the relations of the infundihulum ethnioidalc. Compare with figure 6. 

 The most ventral of the frontal furrows oi- i)its nic referred to throughout this 

 paper as the first (1), the next in order as the second \'l), etc. 



even and unbroken and gives no evidence of the later configura- 

 tion and complexity which characterizes the region in the adult 

 nose. Coronal sections and transections of the recessus frontalis 

 of a 4-month fetus show the lateral nasal plate of cartilage 

 thickened at certain points. These thickened cartilaginous 

 areas- -the forerunners of the folds or accessory conchae which 

 later configure the lateral wall of the recessus frontalis — vary 

 in number and are for a period low and inconspicuous and do 

 not throw the nasal mucosa into relief. 



Upon examining the recessus frontalis in the late fetus, one 

 finds a variable number of low accessory conchae on its lateral 

 wall (figs. 1 to 4). The folds with the cartilaginous skeleton, 



