The vomer is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the septum of the nose (fig. 379); it has two surfaces and four borders. Each surface (fig. 380) is marked by small furrows for blood-vessels, and is traversed by a groove, which runs obliquely downwards and forwards, and lodges the corresponding long sphenopalatine nerve and vessels. The superior border is the thickest, and presents a deep furrow bounded on each side by a projecting ala; the furrow receives the rostrum of the sphenoid; the ala articulate with the sphenoidal concave, the sphenoidal processes of the palatine bones and the vaginal processes of the medial pterygoid plates. The inferior border articulates with the nasal crest formed by the maxillae and palatine bones. The anterior border is the longest; its upper half articulates with the perpendicular plate of the ethmoid, its lower is cleft for the reception of the inferior margin of the cartilage of the septum of the nose. The posterior border is free, concave, and separates the posterior nasal apertures; it is thick and bifid above, thin below. The anterior end of the vomer articulates with the posterior margin of the incisor crest of the maxillae and projects downwards between the incisive canals.
Figure 379
Ossification,-At an early period the septum of the nose consists of a plate of cartilage. The superior part of this cartilage is ossified to form the perpendicular plate of the ethmoid ; its antero-inferior portion persists as the septal cartilage, whilst the vomer is ossified in the membrane covering its postero-inferior part. About the eighth week of fetal life two centres of ossification, one on each side of the median plane, appear in this part of the membrane, medial to and a little behind the paraseptal cartilages. About the third month these centres unite below the cartilage, and thus a deep groove is formed (fig. 381) in which the cartilage of the septum of the nose is lodged. As growth proceeds, the union of the bony lamellae extends upwards and forwards and at the same time the intervening plate of cartilage undergoes absorption. By the age of puberty the lamellae are almost completely united, but evidence of the bilaminar origin of the bone is seen in the everted alae of its upper border and the groove on its anterior margin. Up to a certain stage the vomer is entirely derived from membrane, but it becomes added to by the ossification of the hinder end of the anterior .paraseptal cartilage. From this part of the ossified anterior paraseptal cartilage a plate of bone descends by the side of the primary part of the vomer, and fuses with it. The vomeronasal cartilage is the persistent part of the anterior paraseptal cartilage.
