

In the posterior two-thirds of the bone the canal is situated nearer the internal 

 surface of the mandible; and in the anterior third, nearer its external surface. It 

 contains the inferior alveolar vessels and nerve, from which branches are dis- 

 tributed to the teeth. The lower border of the ramus is thick, straight, and con- 

 tinuous with the inferior border of the body of the bone. At its junction with the 

 posterior border is the angle of the mandible, which may be either inverted or everted 

 and is marked by rough, oblique ridges on each side, for the attachment of the 

 Masseter laterally, and the Pterygoideus internus medially; the stylomandibular 

 ligament is attached to the angle between these muscles. The anterior border is 

 thin above, thicker below, and continuous with the oblique line. The posterior 

 border is thick, smooth, rounded, and covered by the parotid gland. The upper 

 border is thin, and is surmounted by two processes, the coronoid in front and the 

 condyloid behind, separated by a deep concavity, the mandibular notch. 



The Coronoid Process (processus coronoideus) is a thin, triangular eminence, 

 which is flattened from side to side and varies in shape and size. Its anterior 

 border is convex and is continuous below with the anterior border of the ramus; 

 its posterior border is concave and forms the anterior boundary of the mandibular 

 notch. Its lateral surface is smooth, and affords insertion to the Temporalis and 

 Masseter. Its medial surface gives insertion to the Temporalis, and presents 

 a ridge which begins near the apex of the process and runs downward and forward 

 to the inner side of the last molar tooth. Between this ridge and the anterior 

 border is a grooved triangular area, the upper part of which gives attachment 

 to the Temporalis, the lower part to some fibers of the Buccinator. 



The Condyloid Process (processus condyloideus] is thicker than the coronoid, 

 and consists of two portions: the condyle, and the constricted portion which sup- 

 ports it, the neck. The condyle presents an articular surface for articulation with 

 the articular disk of the temporomandibular joint; it is convex from before back- 

 ward and from side to side, and extends farther on the posterior than on the ante- 

 rior surface. Its long axis is directed medialward and slightly backward, and if 

 prolonged to the middle line will meet that of the opposite condyle near the ante- 

 rior margin of the foramen magnum. At the lateral extremity of the condyle 

 is a small tubercle for the attachment of the temporomandibular ligament. The 

 neck is flattened from before backward, and strengthened by ridges which descend 

 from the forepart and sides of the condyle. Its posterior surface is convex; its 

 anterior presents a depression for the attachment of the Pterygoideus externus. 



The mandibular notch, separating the two processes, is a deep semilunar depres- 

 sion, and is crossed by the masseteric vessels and nerve. 



Ossification. The mandible is ossified in the fibrous membrane covering the outer surfaces 

 of Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch (see 

 p. 66), and are two in number, a right and a left. Their proximal or cranial ends are connected 

 with the ear capsules, and their distal extremities are joined to one another at the symphysis 

 by mesodermal tissue. They run forward immediately below the condyles and then, bending 

 downward, lie in a groove near the lower border of the bone; in front of the canine tooth they 

 incline upward to the symphysis. From the proximal end of each cartilage the malleus and 

 incus, two of the bones of the middle ear, are developed; the next succeeding portion, as far as 

 the lingula, is replaced by fibrous tissue, which persists to form the sphenomandibular ligament. 

 Between the lingula and the canine tooth the cartilage disappears, while the portion of it below 

 and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. 



Ossification takes place in the membrane covering the outer surface of the ventral end of 

 Meckel's cartilage (Figs. 178 to 181), and each half of the bone is formed from a single center 

 which appears, near the mental foramen, about the sixth week of fetal Life. By the tenth week 

 the portion of Meckel's cartilage which lies below and behind the incisor teeth is surrounded and 

 invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appear- 

 ance, viz., a wedge-shaped nucleus in the condyloid process and extending downward through 

 the ramus; a small strip along the anterior border of the coronoid process; and smaller nuclei 

 in the front part of both alveolar walls and along the front of the lower border of the bone. These 

 accessory nuclei possess no separate ossific centers, but are invaded by the surrounding membrane 



