Lateral Wall .of the Cavum Nasi in Man. 665 



extremity, or even fused with the ventral extremit}^ of the bullar 

 folds. Ventrally and inferiorly the base of the processus uncina- 

 tus becomes continuous with the surface of the agger nasi. Some 

 observers class the processus uncinatus with the general eth- 

 moidal conchae. 



The accessory folds and furrows of the ascending ramus of the 

 meatus nasi medius, i.e., of the recessus frontalis. In a previous 

 paragraph mention was made of the rather early beginning of 

 an extension of the meatus nasi medius from its ventral and supe- 

 rior part. This extension of the middle meatus towards the frontal 

 region is the first step in the formation of the frontal sinus and 

 certain of the anterior ethmoid cells. To this extension or recess 

 Killian has given the appropriate name, 'Recessus frontalis.' 

 For some time the lateral wall of this recess (ascending ramus of 

 the middle meatus) is even and unbroken. If we examine frontal 

 and horizontal sections of the recess of a 4-months fetus we will 

 find the lateral plate of cartilage thickened at certain points, in 

 the form of projections directed towards the lumen of the nasal 

 fossa. For some time this condition prevails and the mucous 

 membrane is not at first thrown into relief. These thickenings^ 

 which I find vary in number, are in anticipation of the folds 

 (accessory conchae) which are present on the lateral wall of the 

 frontal recess of a later fetus. 



The folds as found in the late fetus are variable in number and 

 as a rule are not very prominent. Their prominence depends 

 largely upon the degree of development of the intervening fur- 

 rows or pits. The folds as a rule more or less lose their identity 

 after birth, and the furrows or pits variously remain as ostia of 

 anterior ethmoid cells. The folds have been appropriately termed 

 frontal folds or conchae, and the bordering furrows or pits, frontal 

 furrows. 



The frontal folds and furrows vary in degree of development 

 and differentiation. We frequently find specimens with four 

 well formed furrows and three resulting folds (fig. 41). In other 

 cases, either by earlier coalescence or, I think better, by a les- 

 sened degree of differentiation, we have a smaller number of 



Journal op Morphology, Vol. 21, No. 4. 



