96 



THE SKELETON. 



two 



Ala. 



With sup. maxill. bones and palafe. 

 FIG. 64. The vomer. 



viduals being frequently bent to one or the other side ; it presents for examination 

 and four borders. The lateral surfaces are smooth, marked by small 

 for the lodgement of blood-vessels, and by a groove on each side some- 



times a canal, the naso-palatine, 

 which runs obliquely downward 

 and forward to the intermaxil- 

 lary suture ; it transmits the 

 naso-palatine nerve. The supe- 

 rior border, the thickest, pre- 

 sents a deep groove, bounded 

 on each side by a horizontal pro- 

 jecting ala of bone; the groove 

 receives the rostrum of the 

 sphenoid, while the alee are 

 overlapped and retained by the 

 vaginal processes which project 

 from the under surface of the 

 body of the sphenoid 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 joins with the palate bones. The upper half of the anterior 

 border usually consists of two laminae of bone, between which is received the 

 perpendicular plate of the ethmoid; the lower half, also separated into two 

 larnellge, receives between them the lower margin of the septal cartilage of the 

 nose. The posterior border is free, concave, and separates the nasal fossae 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, 

 submucous connective tissue. Hence polypi are rarely found growing from this 

 surface, though they frequently grow from the outer wall of the nasal fossae, 

 where the submucous tissue is abundant. 



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, 

 the vomerine cartilage, which is prolonged forward to form the remainder of the 

 septum. Ossification commences in the membrane at the postero-inferior part of 

 this cartilage by two centres, one on each side of the middle line, which extend 

 to form the two laminae. 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. 65) 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 

 above downward. In the median line is a vertical ridge, the symphysis, which 

 extends from the upper to the lower border of the bone, and indicates the point of 

 junction of the two pieces of which the bone is composed at an early period of life. 



