TKITri:KI!('l T LY IX PKI.MATKS 



53 



and meta-conids) turned inwards, wliile the upper molar had these 

 relations reversed. As shown in the accompanying diagram (Figure 39), 

 the opposition of these triangles makes a perfect cutting mechanism, and 

 as (Jope has shown this is effective at every stage of development. If 

 the protocone were at the outer angle of the upper molars, it is impossible 

 to conceive of an effective series of intermediate stages.* 



The first step t towards the crushing function is the development of 



trig art- 



Lower Molar. 



Upper and Lower Molars opposed. 



Upper Molar. 



FIG. 39. Key to Plan of Upper and Lower Molars in trituberculate mammals. Each tooth 

 consists of a triangle (triium) with the protocoue (pr) at the apex. The apex is on the inner side 

 of the upper molars and on the outer side of the lower molars. [In C the upper molar is too 

 far internal and posterior. The protocone of the upper molar should fit into the basin of the 

 talonid of the IUWLT molar. See Figs. 60, 208, 20!>. ED.] 



the hypoconid upon the incipient talonid which is later reinforced by two 

 more cusps, the entoconid and hypoconulid. Tin/* f//c entire //a/ or talonid 

 is complete upon the lower molars before it commences to develop upon tin- 

 upper molars, as shown in Anaptomorphm (Fig. 36, No. 7, and Fig. 40, 

 No. 9, Fig. 130) as well as in the ontogeny. 



Upon the upper molars the talon is only developed in bunodont types, 

 such as the Primates and Ungulates, to still further increase the crushing 

 area of the crowns; it always arises as seen in the Primates (Fig. 40), by 

 a slow upward growth from the cingulum, opposite the protocone. In 

 its early stages the hypocone, hi/, always resembles the early stages of the 

 hypoconid and conclusive proof of its talon-like character is seen among 

 the Condylarthra (Haploconus), in which it appears as a wide separate 

 heel. So far, therefore, from the truth of Fleischmann's supposition that 

 the upper molars have one more element (the " entomere ") than the 

 lower, exactly the reverse is the case, for the lower molars early acquire 

 much the greatest extension of the talon, while retaining all the elements 

 of the trigon. 



* [In opposition to this, however, see the views of Gidley iu Fig. 208. ED.] 

 t[This paragraph appears misleading. See pp. 61*, 68*, 82*. ED.] 



