COMPARATIVE ANATOMY OF THE TEETH. 285 



year, and is found not to be shed before the sixtieth. The 

 sixth and last molar has from twenty-two to twenty-seven 

 plates. Its antero-posterior length in the line of the curv- 

 ature is found to measure from twelve to fifteen inches, 

 and breadth about three and a half inches. 



The mastodon is an extinct race. It has the tusks of the 

 elephant, and differs in its grinders, having their surfaces 

 divided into " wedge-shaped transverse ridges," instead of 

 the numerous vertical plates of the elephant. 



The dental formula is given as twenty-eight ; seven teeth 

 on each side to the upper jaw, and the same number to the 

 lower. This number, however, combines both the decidu- 

 ous and permanent set. 



The hippopotamus. This monster of the waters is exceed- 

 ingly interesting to the dentist, as from its teeth, informer 

 times, were mostly supplied the best artificial substitutes 

 for the human. It was most appropriate for this purpose, 

 as the dentine was extremely hard, and sections of it sus- 

 ceptible of very high polish. The number of teeth, as 

 given by M. Cuvier, is thirty-two, i. e. six molars on each 

 side of each jaw, two incisors on each side of each jaw, and 

 two canines also on each side of each jaw. The three ante- 

 rior molars (the premolars of Mr. Owen) are conical; the 

 posterior present two pairs of points. The upper incisors 

 are short, conical and recurved, the inferior "prolonged, 

 cylindrical, pointed, and horizontally projecting." The 

 upper canine is straight, the lower very large and bent 

 back, recurved. 



Rhinoceros. This genus has no canine teeth. Its in- 

 cisors vary, though the usual number given is eight, two 

 on each side of both upper and lower jaw. The number 

 of molars is twenty-eight. This animal is remarkable for 

 its single horn, though in some varieties there are two. 

 The African rhinoceros is said to have two horns, and no 

 incisors. 



The hog, (suidce.) This family, among the ungulata, 

 comprises the greatest varieties in dentition. The ca- 

 nines form the most prominent feature of this group, 



