294 CROCODILIANS. 



the new tooth grows, the pulp of the old one is removed ; the old 

 tooth itself is next attacked, and the crown, being undermined by the 

 absorption of the inner surface of its base, may be broken off by a 

 slight external force, when the point of the new tooth is exposed, as 

 in the figs. 5 and 7, PI. 75. 



The new tooth disembarrasses itself of the cylindrical base of its 

 predecessor with which it is sheathed, by maintaining the excitement 

 of the absorbent process, so long as the cement of the old fang retains 

 any vital connexion with the periosteum of the socket ; but the frail 

 remains of the old cylinder, thus reduced, are sometimes lifted out of 

 the socket upon the crown of the new tooth, as in fig. 4, h ; when 

 they are speedily removed by the actions of the jaws. This is, 

 however, the only part of the process which is immediately produced 

 by violence : an attentive observation of the more important 

 previous stages of growth, teaches that the pressure of the growing 

 tooth operates upon the one to be displaced only through the medium 

 of the vital absorbent action which it has excited. 



Most of the stages in the development and succession of the 

 teeth of the Crocodiles are described by Cuvier with his w^onted 

 clearness and accuracy ; but the mechanical explanation of the 

 expulsion of the old teeth, which Cuvier(l) adopts from M. Tenon, is 

 opposed by the disproportion of the hard part of the new tooth to the 

 vacuity in the walls of the old one, and by the fact that the matter 

 impressing — viz., the uncalcified part of the tooth-matrix — is less 

 dense than the part impressed. 



No sooner has the young tooth penetrated the interior of the old 

 one, than another germ begins to be developed from the angle 

 between the base of the young tooth and the inner alveolar process, 

 or in the same relative position as that in which its immediate 

 predecessor began to rise, and the processes of succession and 

 displacement are carried on uninterruptedly, throughout the long 

 life of these cold-blooded carnivorous reptiles. 



From the period of exclusion from the egg the teeth of the 

 Crocodile succeed each other in the vertical direction ; none are 

 added from behind forwards like the true molars in Mammalia. 



(I) Ossemens Fossiles, ed. 1836, Tom. ix. p. 182. 



