PLATYRHINES. 439 



jaw both premolars and molars are severally implanted by two 

 fangs ; the canines and incisors, in both jaws have each a single 

 fang, according to the normal mode of implantation of these teeth, 

 which is henceforth not departed from in the Mammalian Class. 

 The deciduous series of teeth in the genus Lemur is : — 



Incisors — ^ ; canines — : molars— := 24. 



2—2 1—1 ' 3—3 



170. Platyrhines. — All the Quadrumana of America are distin- 

 guished from the Apes and Monkeys of the old world by certain well- 

 marked external characters : of these, the position of the nostrils at the 

 sides of the broad nose, whence their collective name, is the most con- 

 spicuous ; but they have a more important dental distinction in the 

 superior number of the premolars, which are |e|, instead of |^; 

 whereby the American Monkeys manifest their closer affinity to the 

 Lemurs, and their inferior position in the zoological scale. 



The small and delicate platyrhine Monkeys commonly known 

 in this country by the name of ' Marmosets,' and forming the 

 genera Hapale and Midas, have but two true molar teeth on each 

 side of both jaws, their dental formula (PI. 114, fig. 8.) being: — 



Incisors '— : canines — ; premolars — : molars ^— : = 32. 



2—2 ' 1—1*^ 3—3 ' 2—2 



In the Jacchus Marmoset (Hapale Jacchus) the crowns of 

 the upper incisors are broad and trenchant, the first being the 

 largest ; but the lower incisors continue, as in the Lemurs, to be 

 long and pointed like the canines, to which they are but little 

 inferior in size. The upper canines present a character which is 

 peculiar among Mammalia to the Quadrumana, viz : a longitudinal 

 groove along the fore-part of the crown. The shape of the crowns 

 of the premolars is shewn in fig. 8, p : they are each implanted by 

 a single fang. The first true molar above has three roots, that 

 below has two ; the second molar has a single root in both the 

 upper and lower jaws. A vacant interspace separates the upper 

 canine from the incisors ; the teeth of the lower jaw form a con- 

 tinuous series, as in Man. 



