256 CHANGES PRODUCED ON THE FACE. 



About the fifth or sixth year, Blandin makes the arches to 

 attain their maximum height ; and as we depart from this 

 period, either forward or backward, they "gradually di- 

 minish." 



The base of the lower jaw exhibits changes during the 

 development of the teeth ; being arched upwards and back- 

 wards in the young and the aged, but lying horizontal in 

 the adult. The angle of the lower jaw is very obtuse in 

 the foetal and young subject ; in the adult it contracts to 

 a right angle ; while in old age it again opens, or returns 

 to the infantile state. The mental prominence, in the infe- 

 rior maxilla, is most projecting when the angle is obtuse, 

 as in the young and the aged ; while in the nearly right 

 angle of the adult it is much less so. The condyloid and 

 coronoid processes, instead of presenting the vertical di- 

 rection of the adult, look backwards and upwards in the 

 child, and the very aged. The coronoid processes in the 

 young, are higher than the condyloid ; in the adult, they 

 are nearly on the same level ; and in the aged they again 

 return to their early state. 



The inferior dental canal does not exist, except in the 

 form of the rudimentary groove, at the earliest periods ; it 

 becomes developed when the alveoli are formed. 



This canal occupies, in the adult, about the middle point 

 between the alveolar arch, and the base of the lower jaw. 

 It is said to be situated precisely at the lower portion of 

 the alveoli, in the young subject; and in the aged, it is 

 found at the superior border from the loss of the alveoli. 

 In first dentition it is large, and gradually disappears on 

 the shedding of the teeth. 



The anterior dental or mental foramen, according to Mr. 

 Duval, is situated, at birth, near to the symphysis ; and in 

 proportion to the development of the teeth, is carried back- 

 wards. At first, it is between the canine and first molar. 

 When the milk teeth are fully developed, it is more poste- 

 rior ; and on the appearance of the large molars, it occupies 

 the point between the two temporary molars, or future 

 bicuspids. 



