EMBRYOLOGIC CONSIDERATIONS 35 



Between the free antero-inferior surface of the bulla and 

 the posterosuperior surface of the processus uncinatus is a 

 narrow interval, the primitive hiatus semilunaris, which is 

 the opening or means of communication between the meatus 

 medius and the infundibulum ethmoidale, the infundibulum 

 developing as the gutter-like channel lateral to the processus 

 uncinatus (Figs. 9, 12, and 14). It is these structures which 

 make the lateral wall of the meatus medius rather compli- 

 cated. Their variations in form and type of development 

 give rise to different locations of the ostia of the anterior 

 ethmoidal cells, and thus influence the manner in which the 

 frontal sinus communicates with the middle meatus. 



The bulla ethmoidalis in some instances appears as a 

 smooth bulging fold in which the cartilage, developing as an 

 extension from the lateral nasal capsule, is evenly rounded 

 in its outline, thus making a single oval fold (Fig. 9). In 

 other cases the cartilage shows a double fold or a deep groove 

 in the single fold, and in some instances two such grooves 

 are seen (Fig. 12). Evidence of this type of formation is 

 sometimes seen in early childhood as a slight groove in the 

 overlying mucosa along the middle portion of the bulla, 

 but in no case did we find the ostium of a bullar cell located 

 so as to indicate that it had its origin in such a furrow. 



The number of ethmoidal conchse into which the lateral 

 ethmoidal mass becomes differentiated varies from three to 

 five. The majority of fetuses examined had three ethmoidal 

 conchse four were not uncommonly present; but only on 

 one side of one specimen were five demonstrable (Fig. 16). 

 Killian would count such a specimen as having six ethmoidal 

 conchse, since he counts the agger nasi plus the processus 

 uncinatus as the first ethmoidal concha, "Erste Haupt- 



