118 SPECIAL ANATOMl GJ Tl L 



On arriving at the incisor teeth, it turns back to communicate with the mental fora- 

 men, giving off two small canals, which run forward, to be lost in the cancellous 

 tissue of the bone beneath the incisor teeth. This canal, in the posterior two-thirds 

 of the bone, is situated nearer the internal surface of the jaw ; and in the anterior 

 third, nearer its external surface. Its walls are composed of compact tissue at 

 either extremity, and of cancellous in the centre. It contains the inferior dental 

 vessels and nerve, from which branches are distributed to the teeth through small 

 apertures at the bases of the alveoli. 



Borders. The lower border of the ramus is thick, straight, and continuous with 

 the body of the bone. At its junction with the posterior border is the angle of the 

 jaw (angulus mandibulae). The angle is either inverted or everted, and marked 

 by rough, oblique ridges on each side, for the attachment of the Masseter externally 

 and the Internal pterygoid internally; the stylomaxillary ligament is attached to 

 the angle between these muscles. The anterior border is thin above, thicker below, 

 and continuous with the external oblique line. The posterior border is thick, 

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

 ramus is thin, and presents two processes, separated by a deep concavity, the 

 sigmoid notch (iiicisura mandibulae). Of these processes, the anterior is the coro- 

 noid, the posterior the condyloid. 



The coronoid process (processus coronoideus) is a thin, flat, triangular eminence, 

 which 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 sigmoid notch. Its external surface is smooth, 

 and affords attachment to the Temporal and Masseter muscles. Its internal 

 surface gives insertion to the Temporal muscle, 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 Temporal, the 

 lower part to some fibres of the Buccinator. 



The condyloid process (processus condyloideus), shorter but thicker than the 

 coronoid, consists of two portions, the coudyle (capitulum mandibulae), and the 

 constricted portion which supports the condyle, the neck (collum mandibulae). 

 The condyle is of an oblong form, its long axis being transverse, and set obliquely 

 on the neck in such a manner that its outer end is a little more forward and a little 

 higher than its inner. It is convex from before backward and from side to side, 

 the articular surface extending farther on the posterior than on the anterior aspect. 

 At its outer extremity is a small tubercle for the attachment of the external lateral 

 ligament of the temporomandibular joint. The neck of the condyle is flattened 

 from before backward, and strengthened by ridges which descend from the fore 

 part and sides of the condyle. Its lateral margins are narrow, the external one 

 giving attachment to part of the external lateral ligament. Its posterior surface 

 is convex; its anterior is hollowed out on its inner side by a depression, the ptery- 

 goid depression (fovea pterygoidea), for the attachment of the External pterygoid 

 muscle. 



The sigmoid notch (incisura mandibulae), separating the two processes, is a 

 deep semilunar depression, crossed by the masseteric vessels and nerve. 



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

 of Meckel's cartilages. These cartilages, one on either side, form the cartilaginous bar of the 

 mandibular arch, being joined at the syraphysis by mesodermal tissue. The proximal end of 

 each cartilage is connected with the periotic capsule, and here serves to form the malleus and 

 incus. The next succeeding portion as far as the lingula is replaced by fibrous tissue to form 

 the sphenomandibular ligament. Between the lingula and the canine tooth the cartilage disap- 

 pears, while the- portion near the syinphysis becomes ossified and incorporated with the incisor 

 division of the mandible. This ossific centre appears in about the sixth week of fetal life /. >-., 

 earlier than in any other bone except the clavicle; ossification is practically complete by the tenth 



