64 THE NASAL ACCESSORY SINUSES IN MAN 



ber of cells may be, or from whatever point they may have 

 had their origin, pneumatization extends from the medial 

 wall of the bulla to the lamina papyracea; and in many 

 instances for a variable distance into the supra-orbital plate 

 of the frontal bone. Occasionally there is a less marked 

 extent into the infra-orbital plate of the maxilla. 



The inferomedial wall of the bulla is usually a well- 

 rounded one (Figs. 9, 27, and 36), but in some cases (Figs. 

 16, 51, and 53) it forms a narrower projection. The varia- 

 tions in the size and form of the bulla not only influence 

 the bullar cells, but also, in conjunction with the variations 

 in the processus uncinatus, determine the width and length 

 of the hiatus semilunaris, the interval between the antero- 

 inf erior surface of the bulla and the posterosuperior surface 

 of the processus uncinatus, which is the opening by means 

 of which the meatus medius communicates with the infun- 

 dibulum ethmoidale. The length of the hiatus semilunaris 

 varies in adult types from 14 to 27 mm., this wide variation 

 being due to the manner in which the anterosuperior end 

 of the processus uncinatus is attached to the bullar fold. 

 Cases in which the hiatus is short show at its anterior 

 border a wide plate, passing between the bulla and the proc- 

 essus uncinatus (Figs. 36, 51, and 56). 



The width of this plate varies from 11 mm. to complete 

 absence. In cases in which the plate is absent (Figs. 27 

 and 38) the hiatus extends upward to the level of the cribri- 

 form plate, thus allowing a closer communication between 

 the recessus infundibularis and the recessus conchalis than 

 is usually found. 



