446 DE. C. I. FOESTTH MAJOE OX 



As a result of this minute analysis we find that there exists no essential difference iii 

 the tooth-pattern of the two supposed genera. 



The roots of the Titanowi/s-Taolars have next to he described. I have elsewhere dealt 

 incidentally with the conditions in Titanomys {Lagodus)* . I was impressed by the 

 fact that the chief points of wear are on the inner side in the upper, on the outer in the 

 lower molars, and that these parts are the first to appear lengthened (vertically) in 

 teeth in a condition intermediate between brachyodonty and hypselodonty, while the 

 outer sides of upper, and the inner sides of lower molars remain, as it were, in a passive 

 condition (for upj)er molars of Titanomys see PI. 39. figs. 1, 2, 5, 13, 14, 19). It then 

 appeared to me that the upper teeth of Titanomys showed the hypselodonty — which, 

 as above demonstrated, is here in fact " accompanied by a gradual and essential change 

 of the pattern of the crown "f — to extend gradually towards the outer side. In the 

 description of the pattern of the ProZ«Y/?is-molars (pp. 452, 453) I have reconsidered my 

 former ^dew, and have been able to show that the obliteration of the original pattern is 

 chieflv the consequence of an atrophy on the outer side ; whereas the secondary pattern 

 is brought about by a new addition, starting from the inner side and directed chiefly 

 inward. It remains none the less true " that the vertical elevation of the crown, the 

 first stage towards hypsodonty, always has its starting-point from the inner side of 

 upper molars "+. I added at the same time that "the inner root (of the upper molars) 

 which ultimately will remain open, gradually extends outward, increasing in size, and 

 receives a coating of enamel "§. It is agaiiist this latter assertion especially that the 

 Hev. Pcre Heude has directed a criticisni, couched in energetic terms Ij. When he 

 begins by saying that I had not demonstrated my assertion, he is perfectly riglit; but I 

 had at the time no other intention than to assert, reserving full demonstration for a 

 work on the Lagomorpha under preparation, as intimated on p. 208. 



The Rev. Pere's arguments are to the effect that the roots of teeth cannot be imagined 

 to receive a coating of enamel, because brachyodonty " est un arret de dcveloppement, 

 une fixation par cessation de mouvement, une deterioration du fut transforme en racine. 

 Consequemment la dent ne jieut revenir a son mouvement initial." In order to 

 demonstrate that " logiquement " hypselodonty is more primitive (" plus ancien ") than 

 brachvodouty, and that " rcellement ces deux faits sont phylogeniquement independants," 

 the Rev. Pere adduces the incisors of Rodentia. " D'aatre part toutes les incisives des 

 Rono-eurs etaut essentiellement hypsodontes et a toutes les epoques, au point qu'elles 

 emportent la definition de I'ordre, il faut admettre qu'elles n'ont pas varie, qu'elles ont 

 un caractere commun fixe, et qu'a ce litre I'hypsodontisme est plus general que le 

 brachyodontisme." 



It is not hypselodonty, as such, which is the more jirimitive condition, but tlie 

 o-rowini;- of a tooth by a persistent pulp. And, since hypselodont teeth continue to 

 o-row by persistent pulps during the greater part or the whole of the animal's life, 



* Proc. Zool. Soc. London, 1S93, p. 206. t //). t Il>. § L. c. 



II ' Memoires coiicernant I'Hist. natiirelle de TEmiare Chinois, jiar dcs Pures de la Compagnie de Jesus,' t. ir. 

 p. 75 (1808). 



