DEVELOPMENT OF THE PERMANENT TEETH. 803 



During the general adhesion of the dental groove occurring at the fifteenth 

 week, the part posterior to the last temporary molar follicle continues unob- 

 literated, and thus forms a cavity of reserve, in the fundus of which a 

 papilla ultimately appears, and forms the rudiment of the first permanent 

 molar tooth : this takes place very early, viz., at the sixteenth week. The 

 deepest part of this cavity is next converted by adhesion into a sac, which 

 encloses the papilla, whilst its upper portion elongates backwards so as to 

 form another cavity of reserve, in which, at the seventh month after birth, 

 the papilla for the second molar tooth appears. After a long interval, during 

 which the sac of the first permanent molar and its contained tooth have 

 acquired great size, and that of the second molar has also advanced con- 

 siderably in development, the same changes once more occur, and give rise to 

 the sac and papilla of the wisdom tooth, the rudiments of which are visible 

 at the sixth year. The subsequent development of the permanent molar 

 teeth takes place from these sacs just like that of the other teeth. 



Calcification begins first in the anterior permanent molar teeth. Its order 

 and periods may be thus stated for the upper jaw, the lower being a little 

 earlier : First molar, five or six months after birth ; central incisor, a little 

 later ; lateral incisor and canine, eight or nine months ; two bicuspids, two 

 years or more ; second molar, five or six years ; third molar, or wisdom 

 tooth, about twelve years. 



Fig. 561. 



Fig. 561. PART OP THE LOWER JAW OF A CHILD OP THREE OR FOUR YEARS OLD, 



SHOWING THE RELATIONS OP THE TEMPORARY AND PERMANENT TEETH. 



The specimen contains all the milk-teeth of the right side, together with the incisors of 

 the left; the inner plate of the jaw has been removed, so as to expose the sacs of all the 

 permanent teeth of the right side, except the eighth or wisdom tooth, which is not yet 

 formed. The lai'ge sac near the ramus of the jaw is that of the first permanent molar, 

 and above and behind it is the commencing rudiment of the second molar. 



Eruption of the permanent teeth. The time at which this occurs in regard 

 to each pair of teeth in the lower jaw is exhibited in the subjoined table. 

 The corresponding teeth of the upper jaw appear somewhat later. 



Molar, first 6 years. 



Incisors, central . . . . . . . . 7 



lateral ........ 8 



Bicuspids, anterior 9 



,, posterior . , . . . . 10 



Canines 11 to 12 



Molars, second . . . . . . 12 to 13 



third (or wisdom) . . . . 17 to 25 



3 G 2 



