THE VOMER, THE INFERIOR MAXILLARY BOXE. 



201 



Ate. 



With sup. mar\U. bones and palate. 

 FIG. 165. The vomer. 



The Vomer. 



The Vomer (vomer, a ploughshare) is a single bone, situated vertically at the 

 back part of the nasal fossa?, forming part of the septum of the nose. It is thin, 

 somewhat like a ploughshare in form ; but it varies in different individuals, being 

 frequently bent to one or the other side ; it presents for examination two surfaces 

 and five borders. The lateral surfaces are smooth, marked by small furrows for 

 the lodgment of blood-vessels, and by a groove on each side, sometimes a canal, 

 the n'tso-paJatirc'. which runs 

 obliquely downward and forward 

 to the intermaxillary suture ; it 

 transmits the naso-palatine nerve. 

 The po*t'. /"'Superior border, the 

 thickest, presents a deep groove. 

 bounded on each side by a hori- 

 zontal projecting ala of bone ; 

 the groove receives the rostrum 

 of the sphenoid, whilst the ala? 

 are overlapped and retained by 

 lamina? (the vaginal processes) $* 

 which project from the under 

 surface of the body of the sphe- 

 noid at the base of the pterygoid 

 processes. At the front of the 

 groove a fissure is left for the transmission of blood-vessels to the substance of 

 the bone. The inferior border, the longest, is broad and uneven in front, where 

 it articulates with the two superior maxillary bones; thin and sharp behind, 

 where it j"in> with the palate bones. The upper half of the antero-superior bor- 

 d / usually consists of two lamina? of bone, between which is received the per- 

 pendicular plate of the ethmoid : the lower half, also separated into two lamina?, 

 receives between them the lower margin of the triangular cartilage of the nose. 

 The anterior border is short and vertical, and articulates with the posterior mar- 

 gin of the incisor crest of each superior maxilla. The posterior border is free, 

 concave, and separates the nasal fossa? behind. It is thick and bifid above, 

 thin below. 



The surfaces of the vomer are covered by mucous membrane, which is inti- 

 mately connected with the periosteum, with the intervention of very little, if any, 

 subuiucous connective tissue. 



Development. The vomer at an early period consists of two laminae, separated 

 by a very considerable interval, and enclosing between them a plate of cartilage, 

 which is prolonged forward to form the remainder of the septum. Ossification 

 commences in it by a single centre about the eighth week. From this nucleus the 

 two laminae are formed. They begin to coalesce at the lower part, but their union 

 is not complete until after puberty. 



Articulations. With six bones : two of the cranium, the sphenoid and ethmoid ; 

 and four of the face, the two superior maxillary and the two palate bones ; and 

 with the cartilage of the septum. 



The vomer has no muscles attached to it. 



The Inferior Maxillary Bone. 



The Inferior Maxillary Bone (the Mandible), the largest and strongest bone 

 of the face, serves for the reception of the lower teeth. It consists of a curved, 

 horizontal portion, the body, and two perpendicular portions, the rami, which join 

 the back part of the body nearly at right angles. 



The Horizontal Portion or Body (Fig. 166), is convex in its general outline, and 

 curved somewhat like a horseshoe. It presents for examination two surfaces 

 and two borders. The external surface is convex from side to side, concave from 



