Digestive System Special. 79 



like shears : but the Hysenidse may be distinguished by a. the shape of the crowng 

 of the Incisors, b. the relative strength of Molars and Canines, c. the additional 

 Premolar on each side in both jaws; and d. the basal ridge which girds the coni- 

 cal (for breaking bones) Crown of the second and third Premolar in both jaws, 



4 . 4 

 and defends the subjacent gum. The Viverridse and Canidse have both^? m - 



2.2 

 and m '; in the upper jaw ; but in the former, the Canines are more feeble, 



and have smoother crowns ; the Molar series are less trenchant and more tuber - 



2.2 

 cular; and the inferior true Molars fewer in number, viz., m -. than in tho 



latter. The Canida? are distinguislied by the form of the Incisors ; by having 

 the first lower true Molar anteriorly sectorial, and posteriorly tuberculate ; and 



3 3 



the true Molars below m . '- , 

 3 . 3 



Semi-Planiigrada. The Mustelidoo have great development of the inner tu- 

 bercle of the Sectorial tooth : the Molar series nearly approaches that of tho 

 Hysenidse. 



Plantigrada. All approximate more or less to the dentition of the families 

 of the Ursidse : the dental formula is essentially the same, both in number and 

 kind of teeth, in the genus Ursus, as in the genus Canis. But the chief charac- 

 teristics of the dentition of the Bears are, the development, in the lower jaw, of 

 the true Molar teeth to their typical number in the placental Mammalia ; their 

 general manifestation, in both jaws, of a tuberculate grinding surface : and the 

 reduction in size of the Premolars, of which, the last in the upper jaw {p m 4), 

 becomes more directly and completely opposed to its homotype in the lower jaw 

 than is the case in those species more nearly allied to the typical family of the 

 Order, viz. the Felidse. The true Molar in Meles deserves special notice, on 

 account of its enormous size as compared with its homotype in the two preced- 

 ing Sub- orders. In the Ursidse m 2 is generally considerably developed. 



3 . 3 



Pinnigrada. The Incisive formula never exceeds r -f, ; and in the adult 



"Walrus is reduced to zero in the lower jaw, and one pair in the upper jaw. 

 All possess powerful Canines in both jaws, except Walrus, in which they are 

 absent in the lower jaw; here, however, as if byway of compensation, the 

 upper Canines are of enormous size, tusk-like, with 'persistent pulps,' and com- 

 pelled to pass outside the lower jaw when the mouth is shut. The Molar series 



4.4 1.1 



usually consists oi p m - -; m ~ , a second true Molar being rarely {e.g. 



Otaria) present. In the Phocidee the fang or fangs of all the teeth are usually 

 remarkable for their thickness, which commonly surpasses the long diameter of 

 the crown. There is no special modification of the crown of any tooth by which 

 it can merit the name of a ' sectorial :' and the co- adaptation of the crowns of 

 the upper and lower teeth is completely alternate, each tooth in the lower series 

 being anterior to its fellow in the upper series. 



Proloscidia. Incisors are wanting in the lower jaw, but project 



