THE TEETH OF MAMMALS 179 



usually have two transverse ridges with four 

 cusps. In some forms the oblique ridge, a rem- 

 nant of the tritubercular stage, is retained. The 

 disto-lingual cusp is added to complete the quadri- 

 tubercular form. Some of the American monkeys 

 — as the Marmosets — have sharp cusps, showing 

 an insectivorous diet. The Howlers have large, 

 strong canines projecting from both jaws. The 

 upper have the deep anterior grooves. The pre- 

 molars are trihedral, with three pointed cusps on 

 the buccal line, being triconodont. The true 

 molars are quadritubercular except the last, which 

 is tricuspid. The dentition of the American mon- 

 key is, on the whole, rather low and lemuroid. 

 The Capuchins have lower incisors with broad, 

 thick, wedge-shaped trenchant crowns, which is 

 the characteristic form of these teeth throughout 

 the Quadrumana. The canines are strong and 

 pointed. The upper premolars have two cusps on 

 a transverse line, the outer one being longest and 

 largest. The first premolar below has the trench- 

 ant ridge continued forward from the outer cusp, 

 like the Baboons of the Old World. The true 

 molars decrease in size from first to last, and are 

 all quadricuspid except the third below, which is 

 tricuspid. The dentition in general of the 

 Platyrrhines is thus rather uniform. 



The Catyrrhine, or Old World Monkeys, have 

 the same dentition as man, as to number, and the 



