Lateral Wall of the Cavum Nasi in Man. 631 



conclusion: ''Der Bildungsmodus der Muscheln ist die Resultier- 

 ende zweier Komponenten : (1) des Auswachsens in die Wandpar- 

 tien einwachsender Epithelleisten (Fissuren), (2) des Vorwach- 

 sens bestimmter Wandpartien." 



After a study of these early conditions I am led to believe that 

 the first change in the lateral nasal wall from a more or less even 

 surface (fig. 2) is the production of very shallow grooves, the latter 

 appearing inferior and superior to the position of the primitive 

 concha inferior. These shallow grooves at once throw into slight 

 relief the greater portion of the lateral nasal wall — the anlage of 

 the concha nasalis inferior (maxilloturbinal). I believe that the 

 mesenchymal tissue contained within this primitive fold almost 

 simultaneously undergoes proliferation, thus aiding in early 

 making the fold more prominent. The mucous membrane over 

 the fold may also become thickened, but according to my obser- 

 vations this thickening for the primitive concha inferior is slight. 

 I cannot agree that the formation of a well marked maxillary fold 

 or primitive concha nasalis inferior is wholly due to the forma- 

 tion and deepening of the bordering furrows but, as stated before, 

 I believe that the formation of very shallow grooves is the primi- 

 tive step in conchal formation. The proliferation of the mesen- 

 chyme (probably also the mucous membrane to some extent) 

 aids materially in causing the primitive concha inferior to bulge 

 into the lumen of the nasal fossa, and the bordering furrows to 

 become passively deeper (figs. 10 and 11). 



The ethmoidal fold appears next in the extreme dorsal and supe- 

 rior portion of the nasal fossa, in the angle formed by the lateral 

 wall and the nasal septum in this position (figs. 11 and 13). 

 Since the primitive concha inferior (maxillary fold) takes up the 

 greater portion of the lateral wall at this time there is little room 

 for the primitive ethmoidal fold (fig. 13). For this reason the 

 latter fold arises in part from the septum. Later the nasal fossa 

 increases in the dorsosuperior direction, and with this the primi- 

 tive ethmoidal fold passively migrates from the septum. The 

 mucous membrane over the ethmoidal fold is as a rule thickened, 

 and this thickening causes the primitive fold to show up well in 



