TEETH OF DIPIIYODONTS. 329 



(fig. 261, m 1) consists exclusively of the blade, and plays upon 

 the inside of that of the upper ( sectorial.' This tooth, fig. 261, 

 p 4, above, succeeds and displaces a deciduous tubercular molar, 

 ib. d 4, in all Carnivores, and is therefore a ' premolar ; ' the lower 

 sectorial, ib. m l, comes up behind the deciduous series, d 3, d 4, 

 and has no immediate predecessor ; it is, therefore, a true molar, 

 and the first of that class. By these criteria the sectorial teeth may 

 always be distinguished under every transitional variety of form 

 which they present in the carnivorous series, from Ma chair odus, 

 fig. 293, iv., in which the crown consists exclusively of the ' blade' 

 in both jaws, to Ursus, ib. II., in which it is totally tubercular ; the 

 development of the tubercle bearing an inverse relation to the 

 carnivorous propensities of the species. 



The dentition of the hyama resembles the feline in the reduc- 

 tion of the tubercular molars to a single minute tooth on each side 

 of the upper jaw, and in the inferior molars being all conical or 

 sectorial teeth ; but the molar teeth in both jaws are larger and 

 stronger, and the canines smaller in proportion, than in Felines, 

 from the formula of which the dentition of the hyaena differs 

 numerically only in the retention of an additional premolar tooth, 

 p i above and p 2 below, on each side of both jaws : it is — 



.3.3 1.1 4.4 1.1 



l 373 ;C L1^3.3 ;Wi lTl =34 ' 



The crowns of the incisors form almost a straight transverse line 

 in both jaws, the exterior ones, above, being much larger than the 

 four middle ones, and extending their long and thick inserted 

 base further back ; the crown of the upper and outer incisor is 

 strong, conical, recurved, like that of a small canine. The four 

 intermediate small incisors have their crown divided by a trans- 

 verse cleft into a strong anterior, conical lobe, and a posterior 

 ridge, which is notched vertically ; giving the crown the figure of 

 a trefoil. The lower incisors gradually increase in size from the 

 first to the third ; this and the second have the crown indented 

 externally ; but they have not the posterior notched ridge like the 

 small upper incisors ; the apex of their conical crown fits into the 

 interspace of the three lobes of the incisor above. The canines 

 have a smooth convex exterior surface ; the inner surface is almost 

 flat and of less relative extent in the inferior canines. The first 

 premolar above is very small, with a low, thick, conical crown ; 

 the second presents a sudden increase of size, and an addition of 

 a posterior and internal basal ridge to the strong cone. The third 

 premolar exhibits the same form on a still larger scale, and is 

 remarkable for its great strength. The posterior part of the cone 



