2*78 COMPARATIVE ANATOMY OF THE TEETH. 



The first upper biscupid has its crown of a trihedral shape. 

 The second bicuspid has a pointed talon at its base. 



The crowns of the first two incisors of the lower jaw pre- 

 sent a very peculiar arrangement in the form of a comb. 

 This tooth-like or pectinated appearance, is compared to the 

 little notches on the edge of a a new-formed hunian incisor," 

 though the serrations are much deeper and more numer- 

 ous. These teeth have a single root. The third incisor is 

 thought to resemble a canine, though its crown is described 

 as being broad, horizontal, and having four shallow notches 

 on its margin ; this tooth, also, has a single root. The 

 lower canine, like the upper, has two roots. The milk 

 teeth are twenty-two in number ten to the upper jaw, 

 and twelve to the lower. 



In the cheiromys a resemblance is traced to the rodentia, 

 in the chisel-like incisors of both jaws, which make but a 

 single pair, and are large and curved. The canines are 

 wanting, and a wide space separates the incisors from the 

 molars. 



As the cutting edge of the teeth below does not strike 

 against the "posterior ridge" of those above, M. Blainville 

 supposes that the chisel teeth of the incisors have a differ- 

 ent use from those of the rodents, and that the cheiromys 

 employ them as "cutting pincers to remove the bark of 

 trees, in search of larvae or insects," though the flat, smooth 

 crowns of the molars would seem to show their food not to 

 be entirely of this character. The upper jaw has four mo- 

 lars on each side, and the lower three, placed vertically 

 and parallel. The first upper molar is the smallest, and 

 the second the largest of that jaw. In the lower jaw 

 the last molar is the smallest. A striking contrast with 

 the human molar exists in the roots. In the cheiromys 

 the first and last molars of the upper jaw have but one 

 root ; the two middle have each three roots. In the lower 

 jaw the first molar has two roots, the other two but one. 



INSECTIVORA. This order is regarded as the transition 

 step between the quadrumana and carnivora. The differ- 

 ent genera are remarkable for the varieties in their teeth, 



