

Nan 
Piow Bc—uN Sc - 

abou Bc-o Po 

EXPLANATION OF FIGURES. 
CROWN VIEWS OF SLIGHTLY WORN CHEEK-TEETH OF MURID#. 
a, RIGHT UPPER TEETH; 4, 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. 1.—Cricetus cricetus (five times life size). 
y) 2.—Dicrostonyx sp., m! and my, (ten times life size), of a very young animal from 
Floeberg Beach, Grinnell Land (B. M., 78.5.13.1). 
9) 3-—Arvicola amphibius (seven times life size). 
» 4.—Apodemus efimelas (ten times life size). 
5A podemus*sylvaticus (ten times life size). 
» 6.—Apodemus agrarius (ten times life size). 
4 7-—Micromys minutus (ten times life size). 
» 8.—£pimys 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 (cé Vol. I., Pl. II., 
Fig. 1A); 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 Zvotomys and Microtus (Danmarks Pattedyr, pp. 70, 77; 
Figs. 274, 306). In Murine, Winge regards the cusps here called x! and 6 as the homologues of 
6 and 7 in the Microtine ; 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. Kjib, 1882, 
Pl. ii., Fig. 10/, and Danmarks Pattedyr, pp. 86, 93, Figs. 334, 424). 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. 1a, 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 Muride, e.g. some of the American Cricetine and the Malagasy Nesomyzne ; in all 
Microtine and Murine 2 has fused with cusp 4, and has completely disappeared. 
