686 Jacob Parsons Schaeffer. 



cells that communicate with the middle meatus in the location of 

 the latter two places are usually very small. 



The anterior ethmoidal cells that develop in the region of the 

 ascending limb of the middle meatus, i.e., in the region of the 

 frontal recess, are very variable in size and position. The number 

 of adult cells depends largely upon the degree of differentiation 

 of frontal furrows in the fetus. Some of the cells in this position 

 open directly into the middle meatus, others into the superior and 

 ventral extremity of the infundibulum ethmoidale. Some also 

 open into the suprabullar recess. Some of these anterior eth- 

 moidal cells may extend towards the frontal sinus so that it is 

 difficult to say whether the cavity is that of a frontal sinus or that 

 of an anterior ethmoidal cell. The ventral and superior end of the 

 infundibulum ethmoidale also frequently expands into an anterior 

 ethmoidal cell, which at times is large. 



The conchal cells 



As was stated in a previous paragraph there is no uniformity in 

 the development and arrangement of the cells of the ethmoid 

 labyrinth. It will be recalled that the cells develop from pre- 

 formed furrows, and that the former gradually extend into the 

 lateral masses of the ethmoid bone. In this manner the lateral 

 ethmoidal masses which were primitively solid structures become 

 more or less labyrinth-like as age advances. The individual 

 cells are usually separated by thin osseous plates, or as in some 

 adult cases, merely by mucous membrane — the bony partition 

 having been resorbed . Again the intervening walls may be entirely 

 gone and one or the other group of cells may be replaced by a 

 large cavity. Many of the ethmoid cells are completed by the 

 articulation of the ethmoid with neighboring bones. 



These cells in many cases are not confined to the limits of the 

 lateral ethmoidal masses. They hollow out the superior and 

 supreme ethmoidal conchae so that in the adult these conchae 

 are merely thin shell-like medial boundaries of posterior ethmoidal 

 cells. The cells also at times extend into the sphenoidal sinuses, 



