440 QUADRUMANES. 



The lemurine character of the long, narrow, inferior incisors 

 continues to be manifested by the Sakis {Pithecia, Illig.)» which, 

 like the larger species of Platyrhines called Howlers, Capuchins, 

 and Spider-Monkeys, have the normal number of true molar 

 teeth in the Quadrumanous Order, their dental formula being : — 



J . 2-2 . 1-1 3-3 3-3 



Incisors — : canines — : premolars — ; molars — : = oo. 



2—2 ' 1— 1 ' ^ 3-3 ' 3-3 



The Capuchin Monkeys, {Cebus, PL 1 1 4, fig. 9) have the four 

 lower incisors {i) with broad, thick, wedge-shaped trenchant crowns ; 

 a form which these teeth retain with slight modifications throughout 

 the rest of the Quadrumanous Order. In the Howlers, {Mycetes), 

 the incisive margin of the lateral lower incisors is more produced ; 

 these are larger than the middle incisors, the proportions of the 

 upper incisors are reversed. The canines (c) are strong and well- 

 developed in both jaws ; those above being marked by the deep 

 anterior groove ; there is also a second longitudinal groove on the 

 inner surface of the crown near its posterior margin. The canines 

 are relatively stronger than in the Marmosets ; especially in the 

 male Capuchins. The upper premolars (p) have their crown divided 

 into two trihedral pointed cusps on the same transverse line, the 

 outer one the longest and largest : the transverse diameter of these 

 teeth exceeds their antero-posterior diameter. The first premolar 

 below differs in form from the rest, a short trenchant ridge being 

 continued forwards from the outer cusp, and opposing itself to the 

 inner surface of the canine tooth above : the two cusps of the 

 second and third premolars are less unequal than those above, 

 and the inner one is the most produced. The true molars (m) 

 decrease in size from the first to the third, which is tricuspid below, 

 the rest being quadri-cuspid. In the Spider-monkeys (Ateles) the 

 second true molar below is larger than the first ; and in the 

 Howlers {Mycetes) both the second and third lower molars ex- 

 ceed the first in size, and the middle one is the largest above, 

 (PI. 114, fig. 10). In the attrition of the crowns by mastication, 

 the inner tubercles of the upper molars, and the outer ones of 

 the lower molars, are the first to yield ; but the sub-trenchant 



