THE VOMER 



171 



and palatine bones. The anterior border is the longest and slopes downward and 

 forward. Its upper half is fused with the perpendicular plate of the ethmoid; 

 its lower half is grooved for the inferior margin of the septal cartilage of the nose. 

 The posterior border is free, concave, and separates the choanse. It is thick and 

 bifid above, thin below. 



Rostrum of sphenoid 



Crest of nasal bones 

 Frontal spine 



Space for triangular 

 cartilage of septum ' 



Crest of palatines 

 Crest of maxillae 



FIG. 173. Median wall of left nasal cavity showing vomer in situ. 



Ossification. At an early period the septum of the nose consists of a plate of cartilage, the 

 i thmovomerine cartilage. The postero-superior part of this cartilage is ossified to form the per- 

 pendicular plate of the ethmoid; its antero-inferior portion persists as the septal cartilage, while 

 the vomer is ossified in the membrane covering its postero-inferior part. Two ossific centers, 

 c >ne on either side of the middle line, appear about the eighth week of fetal life in this part of 

 l he membrane, and hence the vomer consists primarily of two lamellae. About the third month 



Alec. 



FIG. 174. The vomer. 



FIG 175. Vomer of infant. 



these unite below, and thus a deep groove is formed in which the cartilage is lodged. As 

 growth proceeds, the union of the lamellae extends upward and forward, and at the same time the 

 intervening plate of cartilage undergoes absorption. By the age of puberty the lamellae are almost 

 completely united to form a median plate, but evidence of the bilaminar origin of the bone is 

 seen in the everted ate of its upper border and the groove on its anterior margin. 



