26 THE NASAL ACCESSORY SINUSES IN MAN 



the conchse, each groove becoming a meatus which is named 

 in accordance with the concha beneath which it lies. 



A sixty-day fetus further shows on the anterosuperior 

 portion of the lateral nasal wall, just anterior to the eth- 

 moidal fold, a smaller prominence representing the early 

 formation of the agger nasi or nasoturbinal. From the 

 posterior portion of the agger nasi there is seen in the sixty- 

 five-day embryo (Fig. 6) a ridge of mesenchyme extending 

 in a postero-inferior direction along the superior curved 

 border of the concha inferior. 



This ridge, which has its free edge directed postero- 

 superiorly and slightly medially, is the early processus un- 

 cinatus, in which there soon appears a thickening or con- 

 densation of the mesoderm in its central portion, followed 

 by transformation into cartilage (Fig. 9). The agger nasi 

 with the processus uncinatus together form the "Erste 

 Hauptmuschel" of Killian. However, in this work it will 

 not be listed as one of the conchae, for, although comparative 

 anatomy shows these structures to be the homologue of the 

 inferior olfactory concha as found in lower mammalia, yet 

 the form and position which they have assumed in the human 

 type are such that we deem it best not to consider them 

 as forming one of the true nasal conchse. 



Shortly after the appearance of the processus uncinatus 

 there is seen, just inferior to the attachment of the middle 

 portion of the concha media, another projection, which also 

 develops from the lateral nasal wall, with its free border 

 facing in an antero-inferior and slightly medial direction 

 (Fig. 9). This fold is the early bulla ethmoidalis, which 

 develops from the lateral ethmoidal mass as one of its sec- 

 ondary folds. 



