666 Jacob Parsons Schaeffer. 



folds and furrows (fig. 40). In fig. 41 it will be noticed that the 

 processus uncinatus is continuous with the first and second 

 frontal folds. The processus uncinatus in the latter case also 

 sends a fork towards the agger nasi, and gains slight fusion with 

 the lateral surface of the concha nasalis media. The superior 

 bullar fold is in part directly continuous with what might be 

 termed the third frontal fold. In fig. 38 we find that the pro- 

 cessus uncinatus is continued ventrally and superiorly to the 

 agger nasi; in part fusing with the concha nasalis media at this 

 point. The superior and inferior bullar folds in the latter instance 

 are continued superiorly to become continuous with the first 

 and second frontal folds. Note that the third frontal furrow is 

 more or less continuous with the suprabullar recess, and that the 

 latter recess continues almost to the cribriform plate of the eth- 

 moid bone. The infundibulum ethmoidale continues ventrally 

 and superiorly into a frontal furrow. Compare this condition of 

 the infundibulum ethmoidale with that found in figs. 39 and 41. 



In fig. 40 there is only one frontal fold or concha differentiated. 

 The concha is bordered by two frontal furrows, and the infun- 

 dibulum ethmoidale is continued ventrally and superiorly into 

 these furrows. In fig. 39 the processus uncinatus is continued 

 ventrally on the lateral wall of the frontal recess and apparently 

 the frontal folds extend from it. In the latter figure note also the 

 relations of the infundibulum ethmoidale in the region of the 

 frontal recess, and the superior and inferior bullar folds and the 

 infundibular fold. 



At times the* frontal folds or conchae fuse with the lateral 

 surface of the concha nasalis media and in this manner we have 

 the obliteration of the frontal recess. In such cases the sinus 

 frontalis must develop from an anterior ethmoid cell, and not 

 by direct extension of the frontal recess (fig. 44). In fig. 36 the 

 frontal folds have not fused with the lateral surface of the concha 

 nasalis media and, therefore, the frontal recess is maintained. In 

 such a condition the sinus frontalis may develop either from the 

 frontal recess or from one or more anterior ethmoid cells. It is 

 difficult to say in the latter figure whether the frontal folds or 



