Development of the Teeth of the Sovicidfo. 



()03 



SoREX ARANKl'S. 



Hie geiii\s of the pennanevt teith. 



Tlie iij)pcr jdtr. 

 Foetus: ho(hf-len;/th about 11 mm. 



At this staije the tooth-band forms a continuous curve, 

 its two halves being connected in the middle. The anterior 

 part of the tootli-band, i. e. the part situated in front of the 

 large functional incisors, is well developed. The tooth-band 

 projects dcoi)ly into the mesoderm, especially the anterior 

 and posterior parts, from which the largest enamel-organs 

 arise. 



The germs of the three functional incisors are well deve- 

 loped. In front of the largest incisor two more tooth-germs 

 are observable, most probably representing two suppressed 

 incisors, V and P (text-figs. 1 & 2; PI. XVIII. fig. 1). As 



Fi- 1. 



Fig. 2. 



e^^\v^ 



rfc^jS 





>? 



:'':fV;!k\ 





Sore.v aranem. — Foetus (11 mm.). Upper jaw. Transverse section. 

 Fig. 1. I'. Fig. 2. r-, witli vestigial milk predecessor (Id-). X 220. 

 The left side of the figm-e represents the lingual and the right the 

 labial side of the jaw. 



appears from the figure, these rudiments are very distinct, 

 seen from the inner side of the tooth-band. We can thus 

 distinguish germs of five incisors, i. e. V, P, P, P, p. I^ 

 and P arc bud-shaped, as are also P and \^, the rudimentary 

 V and P being of course much less differentiated than 1* and 

 I*". I^, the functional first incisor, is bell-shaped. On the 

 lingual side of this tooth the free deep end of the tooth-band, 

 is swollen, forming a bud (PI. XYIII. fig. 1, Zf). Whether 

 this be a tooth-germ or not may be an open question. 



40* 



