1893.] DK. C. J. rORSTTH MA JOE ON MIOCENE SQFIEEELS. 201 



form by tlie addition of the so-called heel or ialon to the original 

 ti'igon. 



The name of heel or talon is borrowed from the teeth of Car- 

 nivora, where this part, as the name implies, generall}- appears 

 in a reduced form compared with the rest of the tooth. In 

 other orders the so-called talon is, as a rule, a well-developed 

 pai't of the inferior molar, so that it seems a priori highly improb- 

 able to consider as a later development that part ^hicli, in the 

 majority of Mammalia, constitutes the whole posterior moiety 

 of the lower molars. What we at present know of the oldest 

 forms of Perissodactyla, Coudylarthra, Eodentia, and eA en of some 

 forms of Creodonta, as revealed especially by the Cernaysian fauna 

 of Eeims\ does not in the least justify a similar assumption. On 

 the contrary, the " talon,'' far from showing a tendency to dis- 

 appear, is in several of these archaic Entheria very prominent, and 

 even more distinctly developed than in any later form, not only 

 in longitudinal extension, but partly even in the elevation of the 

 cusps, as compared with those of the anterior moiety. 



The question of the heel leads us to an objection made by 

 lleischmann, who on the whole accepts the tritnbercular theory, 

 but maintains that the cusps of npper molars are not directly 

 liomologous to those of the lo\\er molars ; or, in other words, that 

 not only does the internal side of upper molars correspond to the 

 external side of Xowev molars, as admitted by Cope and Osborn, 

 but that, besides, the anterior part of upper corresponds to the 

 posterior part of louer molars -. 



In reply to Fleischmaini, Osborn states that "this objection 

 would be fatal to a uniform system of nomenclature for the upper 

 and low er cusps if it could be sustained," but that it is disproved by 

 a comprehensive survey of the Mesozoic tritubex'culates, especially 

 of the Amblotheriidie and Spalacotheriidie '\ Neither Osborn nor 

 J-'leischmann seem to be aware that, if the latter is right, his 

 objection will be fatal not only to the homology of upper and lower 

 cusps, but also to the theory, for the primitive trigon which in- 

 cludes the protoconid, the supposed homologue of the reptilian cone, 

 would in that case be found 1o be formed for the greater part by 

 the very heel which the theory considers to be a late addition. 



There can be no doubt as to the corn^ctnoss of Fleischmann's 

 btatement, which is easy to verify. A left upper anterior milk- 

 tooth of Dvhlph.ijs, for instance, is at first sight very difficult to 

 distinguish from one of tlie right lower series. Even in such 

 specialized molars as tliose of modern Ruminants, in holding side 

 by side a right upper and a left lower molar, or vice versa, what 

 appear to be the mutual homologies are to be traced out even to 



' Lenioinc, •'Etude rl'en.seinblo s\ir Ics dents des Maimai teres fossiles dos 

 fiiviruns do Reims," Bull. Soc. Geul. de Fnince, iii'' bri-io, t. xir. 1801, pp. 

 L'r.;3-2sO, pis. x., xi. 



•* .V. l-"lci8c]iiii;iim, "Die Oriiudl'onii dor liiickziiline boi Siiiigetliieren iind die 

 Ifoinologie der eiii/.clnen Hooker " (Silzungslier. d. k, Preuss. Akud. d. Wiss. 

 Berlin, 1891). 



' Osborn nnd Wortnian, /. c. pp. R4. HA. 



