CHAP. Vl] THE DENTAL SYSTEM OF THE PRIMATES 245 



ANTHROPOIDEA. Simiidae. Hylobates mulleri : a Gibbon 

 from Borneo. 



Dental formula : i, -| ; c, \ ; pm, § ; m, §. (Figs. 169 and 170.) 



The upper teeth. The canine teeth are very long ami slender (cf. 

 Fig. 144) and preceded by the diastema. The premolars are bicuspid 

 with three roots, and the first of the two is caniniform in so far as 

 the outer cusp is much larger than the inner, the latter being very 

 obviously a derivative of the cingulum. In the second premolar tooth 

 such disparity is less distinct, and this tooth is rather larger than the first. 

 The three molar teeth decrease in size successively backwards. Like the 

 premolar teeth, they are implanted by three roots, two external and one 

 internal, and their crowns bear four cusps, two external (lingual) and two 

 internal (buccal) in position. It is important to note that these cusps lack 

 the transverse connecting ridges which are so characteristic of Cercopithecidae, 

 but which are here replaced by an oblique ridge uniting the antero-internal 

 with the postero-external cusp. The same arrangement obtains in the 

 Hominidae (cf. p. 289). The third molar tooth bears signs of degeneration, 

 two posterior (lingual and labial) cusps and the oblique ridge being in some 

 cases vestigial and indistinct. 



The lower teeth (Fig. 170) situated behind the canine tooth are implanted 

 by two roots each, these roots being anterior and posterior in position as is 

 the general rule in the Primates. The lower and upper canine teeth corre- 

 spond in development, and it is noteworthy that traces of lateral compression 

 are perceptible in these teeth. The lower post-canine teeth still present signs 

 of lateral compression though this feature is less conspicuous than in the 

 Lemurs and even the Cercopithecidae ; for a process of antero-posterior 

 reduction is now being initiated, with the result of rendering the crowns of 

 the teeth equilateral in proportions. 



The first of the two premolar teeth fcf. Fig. 169) bears one very large 

 (lingual) and a much smaller (labial) cusp ; it is larger than the succeeding 

 tooth, the crown of which is furnished with two small cusps, behind which an 

 undoubted though minute talon is seen. 



The lower molar teeth vary in different specimens, but the second tooth 

 would seem to be the largest, next to this the first, though this and the third 

 are in some cases equal in bulk. The crowns bear four or five cusps ; viz. an 

 anterior pair (external and internal) which may be connected by a transverse 

 ridge 1 ; and a posterior pair not so connected, and between which a fifth 

 minute cusp may be seen : the last-mentioned cusp may be regarded as 

 representing in a reduced form the bicuspid talon, so conspicuous in the 

 Cercopithecidae (nupra). Finally, it should be noted that in the reduction 

 affecting these cusps, the inner (lingual) posterior cusp is involved to a 

 greater extent than the outer. This affects a point of controversy to which 

 attention has already (p. 244, footnote) been drawn. 



1 This is seen in a specimen in the writer's possession. 



