16 ARKIV FÖR ZOOLOGI. BAND 7. N:0 2. 



vertically to the surface. In some places regular bushes of 

 dentinal tubes are sent off from such cells. This layer may 

 be rightly regarded as ossified pulp which finally may fill up 

 the cavity of the root more or less completely. 



A section through the side wall of the pulpcavity in 

 this stage of development (fig. 6) shows thus four layers l:o 

 the exteriör coat of cement (c), 2:o the Jayer of »calcigerous 

 cells» belonging to the dentine proper (cd), 3:o the layer of 

 dentinal tubes [d), and 4:o the layer of ossified pulp [ojj) with 

 odontoblasts with branched prolongations. 



At the upper end of the pulpcavity this fourth inner 

 layer of ossified pulp is not developed as yet and the layer 

 of normal dentine is there the thickest. 



c cd cL 



Wl^^ 



Ipl 





Fig. 6. Longitudina] section through a portion of the side wall of the 

 pulpcavity of a tooth of Steno frontatus. c cement, cd layer of calcigerous 

 cells in the dentine, d dentine, op ossified pulp. 



The teeth of the Blackwhale (Globicephalus) have also a 

 structure similar to the same in the Dolphin. A tooth mea- 

 suring about 35 mm. of a semiadult Globicephalus has been 

 sectioned (fig. 7). It has a conical crown which is about 11 

 mm. in length and capped with a layer of enamel which near 

 the tip has a thickness of O, is to 0, 2 o mm. The coat of 

 cement is in this not very old tooth quite thin to begin with 

 and does not in any place on my sections attain a thickness 

 which is equal to the enamel cap. With low magnifying 

 power the dentine looks stratified but the different strata are 

 not very sharply defined. The »calcigerous cells» are found 

 as usual chiefly in a layer inside the coat of cement in the 



