INTRODUCTION 



11 



parison of the molar teeth of nearly all mammals, and similar names can be 

 given to the cusps in the upper and lower molar teeth respectively. 



This tritubercular molar owed its survival to three features: (1) the 

 original advantage of its triangular form as expressed in the term "trigo- 

 nodont" proposed by Riitimeyer; (2) the possibility of free addition of 



Fig. 2. — Types of superior molar or grinding teeth. ^4. Bunodont, all conic, Hyra- 

 cothcrium. B. Selenodont, all crescentic, Protoceras. C. Lophodont, all crested, Rhinoceros. 

 D. Buno-selenodont, conic-crescentic, . Paloeosyops. E. Lopho-buuodont, crested-conic, 

 Tapirus. F. Lopho-seienodont, crested-crescentic, Anchitherium. 



new cusps as worked out in detail by Cope, Osborn, Scott, Wortman, 

 Schlosser, and others; and (3) the wonderful independent modeling of 

 these cusps either singly or in pairs into different forms, some remaining 

 rounded, or bunoid, others becoming elongate, crested, or lophoid, others 

 becoming crescentic or selenoid, as show^l in the accompanying figures 

 (Fig. 2). 



Taking the Greek derivatives /Sowo's (hillock), Xo<j!>os (crest), o-tXijvr} 

 (moon, i.e. crescent), and joining them with the word oSoSs (tooth), we 

 have very simple names for the various types of teeth in which all the 

 tubercles passed through the same form. These teeth may be either buno- 

 dont, lophodont, or selenodont. There is a 

 marvelous, independent, adaptive evolution 

 of each cusp; one cusp may remain rounded 

 while its neighbors become crescentic, and 

 we thus find compound patterns, which may 

 be given the somewhat cacophonous terms 

 "bunoselenodont," or in the case of the 

 conic-crested form, "bunolophodont." _ .,, „ ^ , . , . • 



' ' Fig. 3. — Skull of the rat, showing 



Diprotodonty, or the enlargement of a extreme diprotodonty of the upper 

 pair of cutting teeth, is an adaptation which and lower incisor teeth. After Mat- 



. . , , . , , , • ■ thew, 1905. 



arises frequently and independently m m- 



sectivores, rodents, monkeys, tillodonts, primitive edentates, and other 

 orders. Sometimes it is the middle pair of incisor teeth, sometimes the 

 second pair which is enlarged, while the surrounding teeth are reduced. 



