TKITri'.KlKTLY IN PRIMATES 



61 



crushers as well as cutters*: they required to break up their food, 

 and consequently a crushing surface was developed in each heel. lu 

 the course of time the animal gave up its cutting and tearing 

 function, and in all the group of animals to which man belongs it 



A 



000 



B 



VAVAV 



E 



F 



\<w, 



J 



FIG. 41. Mechanics of Cusp Addition (diagrammatic). Compare with shaded drawings in 

 Figure 3$. A, the conical stage* (No. 1); B, C, the triconodont stages* (Nos. 2, 3); D, the first 

 triangular stage t (No. 4) ; E, !<', 6, the triangular upper molar, the lower molars, with triangle 

 and heel (Nos. 5. (5, 7, !>) ; H, I, upper and lower molars, with triangle and heel ; /, human type, 

 upper molar*, with four cusps, triangle, and heel (Xos. 10, 11, 12); lower molars, with five cusps, 

 antero-internal cusp having disappeared (No. 8). [Compare this diagram with that of Mr. Gidley 

 on p. 20s. It is now regarded by Professor Osborn as erroneous in several particulars. En. ] 



* Nutc that the upper teeth (Mack) bite outside the lower teeth (see Fig. 221). 



t Note that the protocont's bite inside uf and between the lower teeth (see Fig. 221). 



acquired a purely crushing function, as seen in the teeth of the 

 baboon. As that became necessary, the next step was to transform 

 the entire upper tooth into a crusher as well as the lower, and to 



* [While the anterior and posterior aides of the upper and lower triangles no doubt 

 formed the principal cutting surfaces, yet the principal piercer and crusher in the upper 

 molars is the internal tip of the triangle, namely, the protocone, which opposes the talonid 

 below. The hypocone is an accessory crusher developed to oppose the trigonid and the 

 space back of the preceding lower molar. ED.] 



