906 THE SHAPES OF TEETH [ch. 



the contour-lines as the so-called crochet and anticrochet. In Anchi- 

 therium, erosion goes no farther than the summits of the several 

 cusps or hill-tops. 



These, to my thinking, are the few and simple lines on which we 

 may study the architecture of the Perissodactyle tooth. But to say 

 how far we may rely on the innumerable minor differences of pattern 



Fig. 445 A. Third upper molar of a horse, a, the ecioloph, with its three styles,, 

 separated by two indents (Owen); b, three transverse ridges, the protoloph, mesoloph 

 and metaloph (Osborn); c, c', two lakes, valleys or fossettes ; d, d', what Owen calls 

 the entries of the valleys; x, x' , cols, where a less worn tooth would shew open roads 

 or passes; 'o, o, cusps or conules, the sites of worn-down hills or hillocks. 



B C 



Fig. 445 B and C. The same tooth, but younger and less worn 

 down than A. Diagrammatic. 



as evidence of blood-relationship and evolutionary descent is quite 

 another story, and deserves much more anxious consideration*. 



* In the vast literature of mammalian dentition the foUowing are conspicuous: 

 R. Owen, Odontography, 1845; L. Riitimeyer, Zur Kenntniss der fossilen Pferde, 

 und zu einer vergl. Odontographie der Hufthiere, Verh. Naturf. Ges. Basel, iii, 

 1963; W. Leche, Zur Entwicklungsgeschichte des Zahnsystems der Saugetiere, 

 Bibl. Zool. 1894-5, 160 pp.; E. D. Cope, On the trituberculate type of molar tooth 

 in the Mammalia, Proc. Amer. Philos. Sac. xxi, pp. 324-326, 1885; W. K. Gregory, 

 A half-century of trituberculy, ibid. Lxxiii, pp. 161-317, 1934. 



