ERUPTION OF THE TEETH. 195 



temporary teeth may be gathered from the accompanying 

 figure, in which it will be noticed that the canines lie far 

 above and altogether out of the line of the other teeth, and 

 that a slight degree of overlapping of the edges of the per- 

 manent central and lateral incisors exists. 



The bicuspids lie in bony cells which are embraced pretty 

 closely by the roots of the temporary molars, and it hence 

 happens that extraction of the latter sometimes brings them 

 away in their entirety. 



The first permanent molars are erupted in a manner closely 

 similar to that described as occurring with the temporary 

 teeth ; that is to say, their bony crypts become widely 

 opened out by absorption, the crown passes out, and new 

 bone is rapidly formed which embraces the neck, prior to 

 any considerable length of root being formed. 



Last, then, follows the absorption of the root of the tem- 

 porary teeth, a matter first accurately investigated by my 

 father. The root at or near to its end, becomes excavated 

 by shallow cup-shaped depressions ; these deepen, coalesce, 

 and thus gradually the whole is eaten away. Although ab- 

 sorption usually commences on that side of the root which 

 is nearest to the successional tooth, it by no means invari- 

 ably does so ; it may be, and often is, attacked on the oppo- 

 site side, and in many places at once. 



The cementum is usually attacked first, but eventually 

 dentine, and even enamel come to be scooped out and 

 removed by an extension of the process. That part of the 

 dentine, however, which immediately surrounds the pulp 

 appears to have more power of resistance than any other 

 part of the tooth, and thus often persists for a time as a sort 

 of hollow column. The absorption of the temporary teeth 

 is absolutely independent of pressure ; the varying position 

 of the excavation has already been noticed, and it may be 

 added that in many lower animals, for example, the frog or 

 the crocodile, the growing tooth sac passes bodily into the 



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