THE MOCTH. 



349 



(and also because they appear while the animal is yet sucking) ; the second, 

 comprising the latter, are named replacing teeth (remplacantes), with new, 

 non-deciduous teeth which are not replaced, and are therefore named 

 persistent teeth. (The replacing and persistent teeth are generally included 

 by us in the term permanent.) 



B. TEETH OF SOLIPEDS. The dentition of adult Solipeds is composed 

 of from 36 to 40 teeth, thus distributed in each jaw : male, 6 incisors, 2 

 canines, 12 molars ; female, 6 incisors, 12 molars. With regard to the 

 first dentition, it comprises the incisors and three anterior molars only, the 

 canine teeth and the three posterior molars being persistent. 



The latter teeth those of the second dentition offer in their develop- 

 ment a common, but very remarkable character, rarely met with in the other 

 animals. They are thrust up from the alveoli during the entire life of 

 the animal, to replace the surfaces worn oft' by friction ; so that the crown 

 is formed successively by the various portions of the fang, each of which 

 issues in its turn from the alveolar cavity, 



INCISORS. These are so named because they serve, particularly in the 



THIN SECTION OF THE INNER PORTION OF THE DENTINE AND OF TILE SURFACE 

 OF THE PULP OF AN INCISOR TOOTH. 



Portion in which calcification is complete, showing separate globular masses at 

 the line of junction with the uncalcified substance, 6 ; at c are seen oval masses 

 of germinal matter (cells), with formed material on their outer surface; d, 

 Terminal portions of nerve fibres. 



Herbivora, for the incision (incido. to cut) of the food. They are arranged 

 in the segment of a circle, at the extremity of the jaw, and are distinguished 

 by the names of pincer, intermediate or lateral (mitoyennes), and corner 

 teeth. The pincers are the two middle teeth, the intermediates the next, 

 and the corners occupy the extremities of the incisive semicircle. 



The general form of these teeth is that of a trifacial pyramid, presenting 

 an incurvation whose concavity is towards the mouth. The base of this 

 pyramid, formed by the crown, is flattened before and behind; the 

 summit, or extremity of the fang, is, on the contrary, depressed on both 

 sides ; the shaft of the pyramid offers, at different points of its height, a 

 series of intermediate conformations which are utilised as characteristics 

 of age, the continual pushing outwards of the teeth bringing each of them 

 in succession to the frictional surface of the crown (Fig. 159, 1). 



Examined in a young tooth which has completed its evolution, the free 

 portion exhibits : an anterior face, indented by a slight longitudinal groove, 

 which is prolonged to the root; a posterior face, rounded from side to side; 



