338 A MANUAL OF DENTAL ANATOMY. 



The first preinolars are absent altogether ; the second 

 premolars, following the canines after an interval, are 

 pointed caniniform teeth. The third premolar is some- 

 times lost early, but the fourth persists. 



The molars of the Camel are of the " Selenodont " type ; 

 their derivation from forms already alluded to will be 

 sufficiently obvious to the reader who has mastered the 

 descriptions, and their double crescentic crowns, may 

 be taken as fair examples of simple ruminant patterns, 

 accessory pillars, &c., being added in some of the other 

 groups. 



In all true Ruminants the last true molar of the lower 

 jaw has a third lobe ( 1 ), and the line of the outer surface of 

 the row of teeth is rendered irregular by the anterior edge 

 of each tooth projecting outwards slightly more than the 

 posterior border of the one in front of it. And the devia- 

 tions in the patterns of the surfaces of the molar teeth are 

 so constant and so characteristic that, although the common 

 ruminant pattern is preserved in all, it is often possible to 

 refer an individual tooth to its right genus. 



The Ruminants all have a well-developed milk dentition, 

 which serves the animal for a long time, indeed until after 

 it has attained to its adult dimensions ; thus a sheep has not 

 completed the changing of its teeth till the fifth year, and 

 a calf till the fourth year. But the first permanent molar 

 is in them, as in so many other animals, the first of the 

 permanent set to be cut, and comes up in its place at the 

 sixth month (in the lamb), and hence has a long period of 

 wear before any of the other second teeth are cut. Conse- 

 quently the first permanent molar is, as is seen in Fig. 145, 

 invariably worn down to a much greater extent than the 

 other permanent teeth ; in the specimen figured it has been 



( ; ) Sir Victor Brooke informs me that Neotragus hemprichii, a small 

 Abyssinian antelope, has only two lobes to the third lower molar. 



