Devlopmciil of the Teeth of the Soriolcliu. (ll'J 



!^. Tlio presence of a liiglily rudimentary niilk-dcntition is 

 ascertained. The milk-teeth do not calcify and are 

 resorhcd before birth. 



'.). A rudimentary tooth-germ situated between the npper P' 

 and M', belonging to the milk-dentition and probably 

 representing a suppressed molar, is present. 



10. The result of the tooth-development in Crocidum mssula 

 may be expressed throngh the following formula : — 



r I' r P' P^ P' Mx M^ W W 

 Id' Pd^ PJ ' 

 Pdi Pd. Pd, 

 I. Pi p., P. — M, M, M,. 



The functional set of teeth consists of: — 



PJ'_P F P^ W M- M' 



I. Pi P4 MiMiM," 



Fiitid apecvnen of a Shrew (Crocidura), hodi/-len(jth about 10 mm. 



Tn the collection of microscopic preparations of the 

 Zootomical Institute of the University in Stockholm there 

 are serial sections through the head o£ a foetal shrew, labelled 

 as Neomys fodiens. By a comparison with my own prepara- 

 tions I have come to the conclusion that the object is not a 

 Neomys, but probably a Crocidura, with which animal it 

 agrees above all with respect to the teeth in all essential 

 points. 



The tooth-band is continnous in the upper jaw, but divided 

 into two halves in the lower. 



In neither jaw did I find any traces of suppressed incisors 

 in front of the functional large ones. 



The examination of this foitus confirms the aforesaid 

 result that there are two dentitions in the Sorieidai. 



The teeth are not very ranch differentiated, which was to 

 be expected. On the labial side of the tooth-band the cup- 

 shaped germs of the milk-teeth are to be seen, and on the 

 lingual side the bud-like germs of the permanent teeth are 

 sitiiated. 



The germs of P and P' in the upper jaw and those of I4 

 and P4 in the lower jaw are in advance of the other teeth 

 and are cup- shaped. 



In this foetal specimen, the youngest at my disposal, a 

 predecessor of I4 — the large procumbent incisor — is present. 

 Thus, by the presence of lA^ it is established that the large 



41* 



