244 THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



reduction is again met with in the Simiidae and Hominidae, but must not be 

 regarded as confined to the higher families of the Primates. The molar teeth 

 bear three distinct cusps, two external and one antero-internal, the postero- 

 internal cusp being quite indistinct, especially in the last tooth. The three 

 better marked cusps are connected by rather indistinct ridges 1 . 



ANTHROPOIDEA. Cercopithecidae. Macacus rhesus. 



Dental formula: i, §; c, \; pm, f ; m, §. (Figs. 167 and 168.) 



The canine teeth, which may in male specimens attain very great 

 dimensions (cf. Fig. 28), are preceded in the upper jaw by a distinct diastema. 

 The upper premolar teeth (two in number) are bicuspid but are implanted by 

 three roots. (In the types hitherto considered, the number of roots of the 

 premolar teeth has varied ; in some teeth the root is single, and in others even 

 in the same jaw three roots are present.) The premolar crowns shew signs 

 of antero-posterior flattening as in Cebus, the outer cusp of the first tooth is 

 much larger than the inner, and the two teeth are nearly equal in size. The 

 upper molars bear four cusps, two external (buccal) and two internal (lingual) 

 united in pairs by transverse ridges, and implanted by three roots. The 

 second tooth is the largest, the first and third being nearly equal in size, 

 though the latter may be in some instances reduced. There is no distinct 

 indication of reduction of cusps in the third molar tooth. 



The lower canine tooth corresponds in dimensions to the upper, and the 

 first lower premolar tooth is caniniform, the lingual (internal) cusp being 

 quite overshadowed by the hypertrophied external cusp. In all the lower 

 post-canine teeth the roots are two in number, and the same teeth preserve 

 the lemurine feature of lateral compression, though this is only marked in 

 the first premolar tooth. 



The three molar teeth increase in size progressively backwards : their 

 crowns bear four cusps united in pairs by transverse ridges, and in the last 

 tooth the posterior projection known as the "talon" is well developed and 

 bears one or even two subsidiary cusps. 



Attention is here directed to the presence of the transverse ridges upon 

 the crowns of the molar teeth (whether upper or lower) of the Cercopithe- 

 cidae, to the exclusion of an oblique ridge. 



1 The indistinctness of the postero-internal cusp is important. As will be shewn 

 later (in Chapter xvi) the indistinctness of a particular cusp has been appealed to in 

 support of the human characters of the fossil Pithecanthropus erectus. The point 

 therein raised is that in the lower Primates, the reduction in cusps affects the 

 postero-extemal (metacone) before it modifies the postero-internal cusp or hypocone 

 (while in the Hominidae the postero-internal is the first of the two to shew signs of 

 reduction). Herein the Pithecanthropus is said to agree with the Hominidae, and 

 to differ from the Simiidae. But the incompleteness of this generalization is shewn 

 clearly by the foregoing observation. 



