INFERIOR MAXILLARY BONE. 95* 



the alveolar process ; this ridge and part of the groove afford attachment,, above, 

 to the Temporal ; below, to the Buccinator muscle. 



The Condyloid Process, shorter but thicker than the coronoid, consists of two 

 portions : the condyle, and the constricted portion which supports the condyle, the 

 neck. 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 backwards, and from 

 side to side, the articular surface extending further on the posterior than on the 

 anterior surface. The neck of the condyle is flattened from before backwards, 

 and strengthened by ridges which descend from the fore part and sides of the 

 condyle. Its lateral margins are narrow, and present externally a tubercle for 

 the external lateral ligament. Its posterior surface is convex; its anterior is 

 hollowed out on its inner side by a depression, the pterygoid fossa, for the attach- 

 ment of the External pterygoid muscle. 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, which 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; and, between them, is the 

 attachment of the stylo-maxillary ligament. 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 Sigmoid Notch, separating the two processes, is a deep semilunar depression, 

 crossed by the masseteric artery and nerve. 



Development. This bone is formed at such an early period of life, before, indeed, 

 any other bone, excepting the clavicle, that it has been found impossible at present 

 to determine its earliest condition. It appears probable, however, that it is devel- 

 oped by two centres, one for each lateral half, the two segments meeting at the 

 symphysis, where they become united. Additional centres have also been 

 described for the coronoid process, the condyle, the angle, and the thin plate of 

 bone which forms the inner side of the alveolus. 



CHANGES PRODUCED IN THE LOWER JAW BY AGE. 



The changes which the Lower Jaw undergoes after birth, relate 1. To the alterations effected 

 in the body of the bone by the first and second dentitions, the loss of the teeth in the aged, and 

 the subsequent absorption of the alveoli ; 2. To the size and situation of the dental canal ; and, 

 3. To the angle at which the ramus joins with the body. 



At birth (fig. 58), the bone consists of two lateral halves, united by fibre-cartilaginous tissue, 

 in which one or two osseous nuclei are generally found. The body is a mere shell of bone, con- 

 taining the sockets of the two incisor, the canine, and the first molar teeth, imperfectly partitioned 

 from one another. The dental canal is of large size, and runs near the lower border of the bone, 

 the mental foramen opening beneath the socket of the first molar. The angle is obtuse, from the 

 jaws not being as yet separated by the eruption of the teeth. 



After birth (fig. 59), the two segments of the bone become joined at the symphysis, from below 

 upwards, in the first year ; but a trace of separation may be visible in the beginning of the second 

 year, near the alveolar margin. The body becomes elongated in its whole length, but more espe- 

 cially behind the mental foramen, to provide space for the three additional teeth developed in this 

 part. The depth of the body becomes greater, owing to increased growth of the alveolar part, 

 to afford room for the fangs of the teeth, and by thickening of the subdental portion which enables 

 the jaw to withstand the powerful action of the masticatory muscles ; but the alveolar portion is 

 the deeper of the two, and, consequently, the chief part of the body lies above the oblique line. 

 The dental canal, after the second dentition, is situated just above the level of the mylo-hyoid 

 ridge ; and the mental foramen occupies the position usual to it in the adult. The angle becomes 

 less obtuse, owing to the separation of the jaws by the teeth. 



In the adult (fig. 60), the alveolar and basilar portions of the body are usually of equal depth. 

 The mental foramen opens midway between the upper and lower border of the bone, and the 

 dental canal runs nearly parallel with the mylo-hyoid line. The ramus is almost vertical in 

 direction, and joins the body nearly at right angles. 



In old age (fig. 61), the bone becomes greatly reduced in size; for, with the loss of the teeth, 

 the alveolar process is absorbed, and the basilar part of the bone alone remains ; consequently, 

 the chief part of the bone is beloiv the oblique line. The dental canal, with the mental foramen 

 opening from it, is close to the alveolar border. The rami are oblique in direction, and the angle 

 obtuse. 



