The Sinus Maxillaris in Man. 349 
THE OSTIUM MAXILLARE. 
When considering the embryology of the lateral nasal wall it 
will be remembered that the primitive maxiliary pouch had cer- 
tain relations of importance. These structures were the processus 
uncinatus, the infundibulum ethmbdidale, the hiatus semilunaris, 
and the bulla ethmoidalis. The location of the ostium maxillare, 
of the adult, corresponds to the place of the primitive maxillary 
pouch. This pouch gradually develops into the pyramidal cavity 
of the adult, leaving the place of communication with the infun- 
dibulum ethmoidale at the point of primary evagination. It is, 
therefore, quite evident that these structures which in the embryo 
bore so close a relation to the Anlage of the sinus maxillaris, must 
now bear even more important relations to the ostium maxillare. 
On raising or removing the middle nasal concha, in the adult, 
a rounded elevation—the bulla ethmoidalis, is seen. This 
structure is directed inferiorly and ventrally. Immediately 
beneath it is the well defined curved margin of the processus 
uncinatus of the ethmoid bone. Between these structures there 
is a narrow slit or semilunar cleft—the hiatus semilunaris, which 
is from 15 to 20 mm. long. This is an important opening, for it 
serves as the communication between the meatus nasi medius 
and the gutter-like groove (infundibulum ethmoidale) formed by 
these structures. The bulla ethmoidalis varies considerably in 
size. At times it is feebly developed and again it may assume 
comparatively large proportions. The size of the bulla greatly 
influences the width of the semilunar cleft or hiatus semilunaris. 
The bulla may be so large that its convexity comes in direct con- 
tact with the free margin of the processus uncinatus of the eth- 
moid bone. In other cases the hiatus semilunaris may be of con- 
siderable width. 
It is easy to conclude what effect these conditions will have on 
the ostium maxillare directly, and on the sinus maxillaris indirectly. 
In one case the cleft of communication between the ostium maxil- 
lare and the meatus nasi medius is practically shut off, while 
in the other case a freer communication exists. It must be 
remembered that, even though the bulla touches the free margin 
