XIII 



PHYLUM CHORDATA 



537 



--[ 



In the Pinnipedia there are always fewer than incisors, 



o 



and carnassials are not developed. The pre-molars and molars 

 have a compressed conical pointed form. The prevailing dental 

 formula of the Seals is 



.3 



- = 34. 



In the Walrus the adult formula is 



.113 



i. g, c. j,_p. g, m. g 18. 



The upper canines take the form of large, nearly straight tusks. 



In the large order of the Rodents the dentition is remarkably 

 uniform, and, in all its general characters, resembles what has 



FIG. 1128. Left lower carnassial teeth of Carnivora. /, Felis ; //, Canis ; III, Herpestes; 

 IV, Lutra V, Meles 3 VI, Ursus. 1, anterior lobe (paraconid) of blade; 2, posterior 

 (protoconid) lobe of blade ; 3, inner cusp (metaconid) ; 4, talon (hypoconid.) (After Flower 

 and Lydekker.) 



already been described in the Rabbit. But the second, smaller 

 pair of incisors of the upper jaw is present only in the Hares 

 and Rabbits ; the number of pre-molars and molars varies from 



2 4 33 

 p. g, m. 2 to p. p m. g, 



and they may develop roots. 



In the Insectivora the dentition is heterodont, complete, and 



