Dental Fornm/d of the Mmidji'. 1 (J!) 



uses sliould be applied to ^Juiiche other than voles, it is 

 almost self-evident that any foi'tnula that may be ap})lied to 

 the voles mnst apply e([nally to the Mmi(he at large. Having 

 ineurred a eertain amount oi* responsibility in the matter, 

 I had to prepare a statement of tlie theoretical questions 

 involved for the use of my colleague; and in accordanee 

 with his desire that statement is recorded in the present 

 paper. 



Kellogg's formula, viz., />. -, m.\'^^, is identical with that 



used by Owen, w^lio stated* that in the rodents ^^ the first 

 or anterior of the molar series, whether the number be 2 — 2, 

 3 — 3, or 4 — 4, is a premolar ; it has displaced a deciduous 

 predecessor in a vertical direction.^' But such a replace- 

 ment is entirely unknown in Muridse ; and Owen's formula, 

 lacking the support of any positive evidence, has been 

 abandoned for many years in favour of that now in common 



use, viz., m. \'l' 'l - 



So long ago as 1872, Forsyth Major t was led to suspect 

 that the anterior cheek-tooth, above and below, in Muridae 

 is neither a "molar" nor a "premolar" in the ordinary 

 sense of those terms, but is the posterior milk-molar, which 

 in this family has become persistent in each jaw, tiie per- 

 manent [)remolar {p. 4), normally replacing this toothy having 

 been suppressed. Long afterwards, but independently, 

 while working at Microtin?e, I arrived at a similar con- 

 clusion J. Adopting llensel's tooth notation (which per- 

 sonally I still prefer, although I realize that convenience 

 now forbids its use), both Forsyth jMajor and I used for the 



the Muridne therefore the formula dm. \, w-J"^, which in the 



more usual notation would be expressed as mp. \ m. ^. 



Kellogg cites the views of Forsyth ]\Iajor and myself, hut 

 does not indicate clearly whether he intends to agree with 

 us or not, although he seems to admit that the homologiza- 

 tion of the front lower cheek-tooth in Microtimx^ with mp^^ 

 would afford an explanation of its complexity. 



It is not possible in this place to present fully the case for 

 tlie homologization of the teeth in question with mp. -; but a 

 brief outline and a few facts in illustration of the argument 



* Owen, ' Anatomy of Vertebrates,' 18G8, vol. iii. p. 300. 



t Forsytb Major, "Materiali," Atti Soc. Ital. Sci. Nat. xv. p. 1 1 l' 

 (1872); '' Nageriiberreste," Palaiontogr. xxii. p. 75 (1873); " Tossilcn 

 rferde," Abhandl. scliwoiz. palilontol. Ges. iv. p. iJJ, footnote u (18/ 7). 



X Ilinton, Proc. Geol. Assoc, xxi. 1910. p. -lUO. 



