Devdopment I'f the Teeth of the Soriciila;. 



CI 7 



Tliis is not tlie only case in which a tooth-gcrni occurs in 

 this phice. 



In Krinarei's' europti'u.'t * a cnp-shapcd tooth-rudiment is 

 found behind i\l.j in the lower jaw. 



The milk-teeth. 

 The U2yper jaw. 



Tn stage T. some vesti<i;ial milk-teeth are present, viz. Id*, 

 I'd', and IM'. The first-tnentioned milk-tooth is about 

 to be absorbed. The two others are cup-shaped (PI. XVIII. 

 fig. 8). ViV is less reduced and is still connected with the 

 tooth-band (PI. XVIII. fig. 3). 



I have found no predecessor of P. 



The predecessor of 1'', which is present in both Sorex and 

 Neomys, has disappeared in Crocidura russiila, at least in the 

 stages in question. 



Of the greatest interest is, however, the occurrence of 

 another tooth-rudiment — i\Ix — situated between P* and M^ 

 on the labial side of the tooth-band like the milk-teeth, 

 belonging no doubt to the milk-dentition (text-fig. 9) . As 

 will be seen from the reconstruction figure, this tooth-germ 

 is not related to the preceding P' nor to the following M' 

 (PI. XVIII. fig. 3). 



Fiff. 9. 







j2e;ss^ss»^4 



'•^^-ni^gSEEiW- 



Crocidura russula. — Fc«tus (12| mm.). Upper jaw. Transverse section. 

 Mx, tooth-germ belonging- to the niilk-dention ; Zl, tooth-band. 

 X 220. The left side of the figure represents the lingual, the right 

 the labial side of the jaw. 



If it were regarded as a predecessor of M^ this tooth would 

 be a premolar, a supposition which — if we agree in tlie most 

 probable view that P* in Crocidura is the homologue of P* in 

 Sorex (and Neomys) — would involve that Crocidura, o\', 

 rather, its ancestors, once had five premolars. 



* Ledio, W., /. c. p. 23, pi. iii. figs 18 & 19. 

 Ann. & Mag. N. Hist. Ser. 8. Vol. ix. -11 



