Lateral Wall of the Cavum Nasi in Man. 657 



just as they are in forming the primitive nasal meatuses and 

 conchae. 



From this furrow (primitive infundibulum ethmoidale) the 

 sinus maxillaris develops its anlage in the form of an evagina- 

 tion of the mucous membrane. This maxillary sinus anlage 

 begins to be established from the sixty-fifth to the seventieth day 

 of embryonal life. In a former paper I suggested that primitively 

 the pouching of the sinus maxillaris aided in deepening the infundib- 

 ulum ethmoidale ; thus causing the processus uncinatus to stand 

 out better at an early period. 



Shortly after this we have the first evidence of the bulla eth- 

 moidalis, appearing superior and lateral to the processus uncina- 

 tus. The bulla ethmoidalis is first indicated by special thicken- 

 ings (one or two) of the lateral plate of cartilage — the cartilagin- 

 ous thickenings appearing on its medial surface. At first the 

 bullar anlages do not cause the mucous membrane to bulge 

 towards the lumen of the nasal cavity; hence these early stages 

 pass unobserved unless one examine serial frontal sections through 

 this region. Later, however, say in a 120-day embryo, the car- 

 tilaginous prominences have developed sufficiently to push the 

 mucous membrane on the lateral wall of the meatus medius into 

 relief (figs. 17 and 18). We now have established a fold, or folds, 

 (bullar folds) lateral and superior to the processus uncinatus. 

 If two folds appear there is an intervening furrow. These folds 

 represent the primitive bulla ethmoidalis. Usually the inter- 

 vening furrow, when present, disappears after birth. Occasion- 

 ally, however, an ethmoidal cell develops from this furrow. . 



Thus far no mention has been made of another fold that 

 appears in many cases inferior to the bullar folds and lateral to 

 the infundibulum ethmoidale. Because of its relations to the 

 infundibulum ethmoidale I shall speak of this as the infundibular 

 fold. It is never very prominent and forms in part the lateral 

 wall of the infundibulum ethmoidale. It may persist as a fold 

 after birth, but it generally becomes leveled down to an even sur- 

 face which imperceptibly passes on to the bullar surface. 



It will, therefore, be seen that we have, during the latter half 

 of intrauterine life, fairly well outlined grooves and folds on the 



