MURINE 499 
This system is based upon the work of Winge, Fleischmann, 
Osborn, Forsyth Major, and Hinton’; it is illustrated in 
Plate XXVIII., in which cheek-teeth of Cricetine, Microtine, 
and Murine are comparatively represented. 
In upper cheek-teeth the tubercles of the median row 
(z, y, 2) are usually conspicuously larger than those of the 
outer or inner rows; those of the inner row have their axes 
more nearly vertical than have those of the outer and median 
rows, and in the various sub-families and individual genera of 
Muride this row of tubercles has suffered numerical reduction 
to a more marked extent than have the others. In Afodemus, 
for example, 7z' has three inner tubercles (Pl. XXVIIL., Fig. 4, 
x’, 6, 7); in Epzmys this tooth has two, cusp 7 being lost ; and 
in Dendromyine—an African group—only cusp6 remains. The 
1 Winge (Vid. Med. Nat. For. Kjob., 1882, 15) came to the conclusion that 
three cusps, numbered by him from before backwards, 1, 2, and 3, which are 
prominently developed upon the outer sides of upper and the inner sides of lower 
molars in some Marsupials, Insectivora, and Chiroptera, are the most ancient 
elements of the mammalian molar ; he identified their homologues, or worked out 
their fate, in the teeth of other mammalian orders. Two other cusps, internal in 
upper, external in lower teeth to cusps 1, 2, and 3, were regarded by Winge as later 
additions, and were numbered as 4 and 5. Here, according to Winge, the develop- 
ment of the lower molars stopped ; but in the upper teeth, internally to cusps 4 and 
5, two new ones, 6 and 7, successively appeared. In his great papers on the 
Lagomorpha (Trans. Linn. Soc., Zool. {2), vii. 433, Nov. 1899), and on the genus 
Brachyuromys (Proc. Zool. Soc., 1897, 695), Forsyth Major adopted Winge’s notation 
for the cusps of upper molars ; but he recognised the fact that the evolution of the 
lower molars is in a more and not a éess advanced stage than is that of the upper 
teeth—a result confirmed by Stehlin’s researches upon the dentition of the pigs 
(Abhand. Schwetz. Paleont. Gesellsch., xxvi., 22 e¢ seg,, 1899). Forsyth Major was 
therefore able to identify in lower molars the homologues of the cusps 6 and 7 of the 
upper ones ; in addition he took into account some other elements not recognised by 
Winge, viz., the “intermediate” tubercles. 
It has long been known that the inner and outer sides of upper molars correspond 
respectively with the outer and inner sides of the lower teeth; Fleischmann 
(Sttzungsber. Preuss. Akad. Wiss, Berlin, 1891, ii., 891) went a step further and 
asserted that the anterior and posterior ends of upper molars are respectively 
homologous with the posterior and anterior ends of the lower cheek-teeth ; a lower 
molar is therefore a completely, inverted image of an upper one. This view was 
contested by Osborn (Lull. Amer. Mus. Nat. Hist. 1892, 84), but it has been 
endorsed by Forsyth Major (Proc. Zool. Soc., 1893, 201), and it is supported by 
Hinton’s work. Forsyth Major thought that the cheek-teeth of rodents were derived 
by a process of simplification or reduction from a multituberculate prototype, and in 
this he is followed by von Méhely and Hinton. The latter, in his system of cusp 
notation, takes notice of some ancient elements of the rodent molar which, hitherto, 
have escaped recognition, and gives effect to the results of all the work briefly 
reviewed above, 
