172 



OSTEOLOGY 



Articulations. The vomer articulates with six bones: two of the cranium, the sphenoid and 

 ethmoid; and four of the face, the two maxillae and the two palatine bones; it also articulites 

 with the septal cartilage of the nose. 



The Mandible (Mandibula ; Inferior Maxillary Bone; Lower Jaw). 



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 unite with the ends of the body nearly 

 at right angles. 



The Body (corpus mandibulce) . The body is curved somewhat like a horseshoe, 

 and has two surfaces and two borders. 



Surfaces. The external surface (Fig. 176) is marked in the median line by a 

 faint ridge, indicating the symphysis or line of junction of the two pieces of which 

 the bone is composed at an early period of life. This ridge divides below and 

 encloses a triangular eminence, the mental protuberance, the base of which is de- 



Coronoid process 



TKMPORALIS 



Mental 

 protuberance 



jLnyle 



Oroaoe. for external 

 maxillary artery 



Fio. 176. Mandible. Outer surface. Side view. 



pressed in the center but raised on either side to form the mental tubercle. On either 

 side of the symphysis, just below the incisor teeth, is a depression, the incisive 

 fossa, which gives origin to the Mentalis and a small portion of the Orbicularis 

 oris. Below the second premolar tooth, on either side, midway between the upper 

 and lower borders of the body, is the mental foramen, for the passage of the mental 

 vessels and nerve. Running backward and upward from each mental tubercle 

 is a faint ridge, the oblique line, which is continuous with the anterior border of the 

 ramus; it affords attachment to the Quadratus labii inferioris and Triangularis ; 

 the Platysma is attached below it. 



The internal surface (Fig. 177) is concave from side to side. Near the lower 

 part of the symphysis is a pair of laterally placed spines, termed the mental spines, 

 which give origin to the Genioglossi. Immediately below these is a second pair 

 of spines, or more frequently a median ridge or impression, for the origin of the 

 Geniohyoidei. In some cases the mental spines are fused to form a single eminence, 

 in others they are absent and their position is indicated merely by an irregularity 

 of the surface. Above the mental spines a median foramen and furrow are some- 

 times seen; they mark the line of union of the halves of the bone. Below the mental 



