Fig. 9. 



Fig. 10. 



EXPLANATION OF FIGURES. 



CROWN VIEWS OF SLIGHTLY WORN CHEEK-TEETH OF MURID^. 



a, Right Upper Teeth ; i, Left Lower Teeth. 



All the figures, with the exception of Figs. 2 and 3, are from Miller's " Catalogue of the Mammals of 

 Western Europe " (by kind permission of the Trustees of the British Museum). 



Fig. I. — Cricetus cricetus (five times life size). 

 „ 2. — Dicrostonyx sp., »z' and OTj (ten times life size), of a very young animal from 



Floeberg Beach, Grinnell Land (B. M., 78.5.13. l). 

 „ 3. — A rvicola amphibius (seven times life size). 

 „ 4. — Apodemus epimelas (ten times life size). 

 ,, 5. — Apodemus'syhaticus (ten times life size). 

 ,, 6. — Apodemus agrarius (ten times life size). 

 ,, 7. — Micromys minutus (ten times life size). 

 ,, 8. — Epimys rattus (five times life size). 

 ,, 9. — Epimys norvegicus (five times life size). 

 ,, 10. — Mus musculus (ten times life size). 



The homologous cusps of upper and lower cheek-teeth are similarly lettered or numbered in 

 the figures. In upper teeth cusp 6 equals the " protocone " of trituberculy (cf Vol. I., PI. II., 

 Fig. I a) ; 7 is the " hypocone " ; 4 and 5 are the " para- " and " meta-cones "' ; i and 3 are the 

 " para- " and " meta-styles " ; and y and z are the " proto- " and " meta-conules " respectively. 

 In the microtine tooth (Fig. 2a) the cusps marked 4, 5, 6, and 7 correspond with those so 

 numbered by Winge in upper teeth of Evotomys and Microtus {Danmarks Pattedyr, pp. 70, 77, 

 Figs. 27^, ioh). In Murinix, Winge regards the cusps here called x^ and 6 as the homologues of 

 6 and 7 in the Microtinw ; he further regards y as the major part of 4, and similarly his cusp 5 

 in this sub-family is a compound of the cusps 5, z, 3, and 7 (see Vid. Medd. Nat. For. Kjdb, 1882, 

 PI. in., Fig. loi, and Danmarks Pattedyr, pp. 86, 93, Figs. 33^, 42^). The view of the homo- 

 logies expressed in this plate has been gradually arrived at in the course of many years' work 

 upon the dentition of rodents, and with a knowledge of many facts which cannot be discussed here. 



The ancient cusp 2 (Vol. I., Plate II., Fig. lA, ms) which, according to Winge, is the 

 homologue of the Reptilian cone, and is, therefore, the true " protocone," is present in the teeth 

 of many low Muridce, e.g. some of the American Cricetince and the Malagasy Nesomyince ; in all 

 MicrotincE and Murines 2 has fused with cusp 4, and has completely disappeared. 



