5 THE INFERIOR MAXILLARY BONE. 139 
towards the nasal fossa, whilst its inner edge is in contact with the ala of the 
vomer. 
Connexions.—The palate bone articulates with its fellow of the opposite side, with the 
ethmoid, vomer, sphenoid, superior maxilla, and inferior turbinated bones. 
Ossification.—The palate bones are developed from the ossification of the membrane 
covering the sides of the oral cavity. According to Rambaud and Renault, two primitive 
centres appear about the sixth week of foetal life. From one of these the tuberosity and 
the part of the vertical plate behind the posterior palatine groove is developed ; from the 
other the remainder of the bone is formed, with the exception of the orbital and sphenoidal 
processes which are*derived from secondary centres that make their appearance some- 
what later. Other authorities describe the bone as ossifying from a single centre which 
appears about the end of the second month in the angle between the vertical and hori- 
zontal plates. 
At birth the bone is much longer in its antero-posterior diameter than in its vertical 
height, the converse of its typical adult form. 
THE INFERIOR MAXILLARY BONE. 
The inferior maxilla (mandibula) or mandible, of horse-shoe shape, with the 
extremities upturned, is the only movable bone of the face. Stout and strong, it 
supports the teeth of the lower dental arch, and articulates with the base of the 
cranium, by the joints on either side between 9 
its condyles and the glenoid fossz of the 7 
temporal bones. The anterior or horizontal 
part, which contains the teeth, is called the 
body (corpus); the posterior or vertical por- 
tions constitute the rami (rami mandibule). 
The body (corpus mandibule) displays 
in the middle line in front a faint vertical 
ridge, the symphysis, which indicates the line 
of fusion of the two symmetrical halves, from 
which the bone is primarily developed. In- 
feriorly this ridge 
divides so as to 
enclose, in well- 
marked speci- 
mens,a triangular 
area—the mental 
protuberance (pro- 
tuberantia men- 
talis), the centre 
of which is some- 
what depressed, 
thus emphasising 
the inferior : 
angles, which are Vv 6 4 15 M4 
known as the 
mental tubercles Fra. 110.—THE Lower JAW AS SEEN FROM THE LEFT Spe. 
(tuberamentalia). 
The outer surface 
is crossed by a 
faint elevated 
ridge, the external 
oblique line (linea obliqua), which runs upwards and backwards from the mental 
tubercle to the fore part of the anterior border of the ramus, with which it is 
confluent. A little above this, midway between the upper and lower borders 
of the jaw, and in line with the root of the second bicuspid tooth, the bone 
is pierced by the mental foramen (foramen mentale), which is the anterior opening 
of the inferior dental canal, which traverses the body of the bone. Through this 
10 
11 
Mental tubercle. 7. Coronoid process. 12. Masseter. 
Depressor labii inferioris. 8. Temporal muscle. 13. Angle. 
Mental prominence. 9. Condyles. 14. External oblique line. 
Levator mentis. 10. External pterygoid 15. Platysma. 
Symphysis. muscle, 16. Mental foramen. 
Buccinator muscle. 11. Neck. 17. Depressor anguli oris. 
O SU 99 ko 
Bis, 
