CHAP. Vl] THE DENTAL SYSTEM OF THE PRIMATES 



289 



c 



PA. M. 



PR. HY. 



PRO. HYD 



MD. ENT.D. 



B' C' 



Fig. '207. Human molar teeth and their adjustment. 

 A. Second upper molar tooth with four cusps. 



The same shewing the identity of the cusps, and the oblique ridge 

 joining PR and M. 



The same, shewing the original triangle, to which the cusp HY has 

 been added in Man. 



Second lower molar tooth, with four large cusps and a small inter- 

 mediate cusp posteriorly. 



The same, shewing the identity of the cusps. 



The same, shewing that the cusps marked PRD and MD are regarded 

 as remnants of a triangle previously formed here, while the other 

 three cusps (HYD, HLD and ENT. D) have been added 1 . 



Tracings of the second and third upper molar teeth (marked by thick 

 contour lines) superimposed upon the second and third lower molar 

 teeth. (From the skull of an aboriginal Australian.) 



B. 



A'. 



B'. 

 C. 



1). 



PRD. Protoconid. 

 PAD. Paraconid. 

 MD. Metaconid. 

 HYD. Hypoconid. 

 HLD. Hypoconulid. 

 ENT. D. Entoconid. 

 The Hypoconid, Hypoconulid and Ento- 

 conid together constitute the "talonid." 



In C the mark x shews where the Hypocone of the upper tooth should fall 

 when the teeth close. The asterisk (*) shews where the Protocone of the upper 

 tooth should fall in the same conditions. 



1 Transverse ridges connecting the cusps PRD and MD, and again HYD and 

 ENT. D, are very distinct in the Cercopithecidae and are noticed in the description 

 of the teeth of those animals (r. supra, p. 244). 



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