TEETH OF THE ELEPHANT. 787 



plates of ivory, while all the interstices are filled up by the circumfused 

 cementum. 



(2271.) During the growth of a compound tooth of this description, 

 the enamel-secreting membranes derived from the capsule of the tooth, 

 of course, interdigitate with the ivory-forming pulps that arise from the 

 bottom of the sockets, and thus the hard materials formed by them take 

 the same arrangement. After these structures have been completed, one 

 or other of the sets of pulps, most probably the enamel pulps, changing 

 their action, fill up all the intervening spaces with the crusta petrosa. 



(2272.) As during the growth of a quadruped the size of the jaws is 

 continually increasing, a necessity exists for changing the teeth once or 

 oftener during the life of the animal, in order to adapt these organs to 

 the altered conditions required: hence the necessity for shedding the 

 teeth of young animals, and replacing them with others of larger dimen- 

 sions or more numerous than the first set. 



(2273.) This is effected in two different ways, each of which demands 

 our separate notice. 



(2274.) In most quadrupeds, as, for example, in the Carnivora, the 

 Quadrumana, and the greater number of herbivorous genera, the succes- 

 sion of the teeth is provided for precisely in the same way as in our own 

 species, namely, by the formation of a new tooth below each of the 

 deciduous ones (fig. 399, d d) ; so that when the latter falls out in con- 

 sequence of the absorption of its fangs, the former is ready to take its 

 place. The germ of the second tooth is at first found imbedded in the 

 jaw-bone, in the immediate vicinity of the roots of the one which it 

 is destined to replace ; and as its growth advances, the old and used 

 tooth is gradually removed to make way for the new comer. The steps 

 of this process are exactly similar to those by which the milk-teeth of a 

 child are changed, and the details connected with it are familiar to every 

 anatomist. 



(2275.) But in the Elephant, and some other genera of PACHTBEEMATA, 

 the succession of the teeth is effected in a different manner, the place of 

 the first-formed being supplied by others that advance from behind as 

 the former become used. Animals exhibiting this mode of dentition 

 have the grinding surfaces of their molar teeth placed obliquely * ; so 

 that if they were to issue altogether from the gum, the anterior portion 

 would be much more prominent than the posterior, notwithstanding that 

 the opposed teeth act upon each other in a horizontal plane. The con- 

 sequence of this arrangement is, that the anterior portion of these teeth 

 is ground down to the roots, and worn away sooner than the posterior 

 portion. Moreover the posterior part of the tooth is considerably wider 

 than the anterior ; so that, as the succeeding tooth advances from behind, 

 there is always sufficient room to receive it ; and in this way, by the time 

 that the first tooth is quite destroyed and falls out, a new one from behind 

 * Cuvier, Le9ons d'Anat. Comp. iii. p. 122. 



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