PRESENT PK0BLEM8 IX EVOIJJTION AND HEREDITY. 



:U3 



l)Osterior ling^ual cusp, or liypocone, which, as Co{)v has sliowii, is ex- 

 hibited in various degrees of development in different r;ices and is an 



Fic. 4. 



Evolution of the rrsPfS ok thk human i.owku molar.— ja;"', protuconul (antpricn- biicoal ciiup*: 

 jxi''. paiaciiuid: vic'\ nietaconid (anterior lingual cus])) ; Ini', liypoi^oiiirt (pusteiior buccal): ('(;'. ciilo 

 (•i>ni(i (postcriiii- liii;;ii:il ciisi>) : iiin'^, ine.socomilid (iiitirmccliati' cu^])). Diagram 1. — Ileptiliaii slaiic 

 1 )ia;;raiii,s 2-.'>. — Mt-sdzuic mammals, first lower luolar.s sliowiiif; rise of ancestral cusps. Diagram (i. -- 

 Iviceiie carnivore {uiinris), showing how the low tubercular crown u/-! is derived from the liigli crown 

 /;(/. Diagram 7. — Eocene monkey (AnaptomoriilniK), showing liowthe primitive anterior lingual cus)) 

 y.rt'' disa|)pears. Diagram 8. — Human first molar with its ancestral cusjis. 



important race index.* A glance through the diagiams shows tliat 

 tlie develoi)ment of tlie cr()wn lias been l)y the successive addition of 

 new cusps. Without entering upon the details of evidence, which 



ia.iotx, ' ' 



taloth 



rpiier and lower niohiis op|>ost^d. 



Fli;. :.. 



Kev to i'la.V of ui'PEK and LoWEit MOLAits IN ALL .MAMMALS.— Each toolli consists (»f a triangle, 

 tn<j(jn, with flie protocone, pj-, at tlie apex. Tlie apex is on the inner side of the upi)er molars and on 

 t lic outer side of the lower molars. 



woukl be out of place here, 1 may say, briefly, that the new main cns])s 

 ha\(' developed at the points of maximum wear (/. e., use), and con- 



^ Tho upper molars iu many Esijuimaux arc triangular (aw in Fig. (i, diagram 11); 

 in most negroos they aro square (diagram 12). In our va<'e tliey ;ii(' iritenucdiatc. 



