THE ETHMOID BONE 51 



cecum with the frontal. If the vertical plate be deflected 

 below the cribriform, the crista galli is inclined in the opposite 

 direction. The anterior border of the plate articulates with 

 the nasal spine of the frontal and with the nasal bones; the 

 inferior border in front with the triangular cartilage of the 

 nose, and behind with the vomer; the posterior margin with 

 the sphenoidal crest (Fig. 9). 



Each lateral mass or labyrinth encloses three sets of spaces 

 the anterior, middle, and posterior ethmoidal cells; they do not 

 communicate with each other. Externally is the paper-like 

 orbital plate, or os planum (lamina papyracea), closing in the 

 middle and posterior cells; it articulates in front with the 

 lacrymal, behind with the sphenoid, above with the frontal, 

 and below with the superior maxilla and palate bones. ' On 

 this aspect below the plate is a groove belonging to the middle 

 meatus of the nose; it turns up anteriorly, and is continued 

 by the infundibulum through the anterior ethmoidal cells 

 to the frontal sinus; the middle cells open into the horizontal 

 part of the groove. The lateral mass in front of the orbital 

 plate is covered in by the lacrymal; from this part the uncinate 

 process curves back, down, and out, helping to close the orifice 

 of the antrum; it articulates below with the ethmoidal process 

 of the inferior turbinate. 



The inner aspect of each lateral mass is in the outer wall 

 of the nasal fossa. Above is a channel, the superior meatus, 

 passing from behind to about the middle of the bone; it com- 

 municates with the posterior cells. The plate overhanging it 

 is the superior turbinate process or superior spongy bone (concha 

 suprema); the space above that is in the roof of the nose. 

 Below the groove is the inferior turbinate process of the ethmoid 

 or middle spongy bone (concha inferior), rolling convexly toward 

 the nasal fossa; it forms the lower border of the lateral mass. 



Two grooves cross the upper margin of the lateral mass, 

 forming with the frontal the two internal orbital or anterior 

 and posterior ethmoidal canals. Posteriorly the mass is anky- 

 losed with the sphenoidal spongy bone. 



The cribriform plate occupies the ethmoidal notch of the 

 frontal. It presents the olfactory groove on each side of the 

 crista galli and foramina for the olfactory nerves; the foramina 

 of the middle set are few and are simple perforations; in the 

 external and internal sets they are more numerous, and are 



