LÖNNBERG, THE DENTITION OF DELPHINAPTERUS LEUCAS. 15 



may correspond to the apical layer of dentine described above 

 in the tooth of Delphiiiaj^terus. Otherwise the dentine of 

 Delphinus is not stratified in the same way as in DelyJiinap- 

 terus, but in the root two iayers are plainly visible with low 

 magnifying power, although with liigher the dentinal tubes 

 are seen running directly from one layer into the other. The 

 dentine of the Dolphin is remarkable for its great number of 

 »calcigerous cells» first seen by Anders Retzius^ and then 

 by OwEN.^ These cells are chiefly situated in the most peri- 

 pheric part of the dentine where they form an irregular stra- 

 tum. Towards the basal parts of the root they increase in 

 size and number more and more. Near the end of the root 

 they form a veiy thick exteriör layer with so many large 

 cells that the tissue should have quite the appearance of 

 cement if it was not for the dentinal tubes with which the 

 cells stånd in connection. The outer coat of cement is even 

 at this place sharply defined from the cellulär dentine, 



The teeth of Sieiio frontatus are in its main features built 

 after the same plan as those of the Dolphin, although there 

 are several less important differences. With regard to the 

 outer shape the teeth ot Steno are strongly curv^ed which 

 makes it impossible to obtain a central longitudinal section 

 in one plane. The curving is double. The root is strongly 

 curved backwards and the crown somewhat inwards with the 

 tip. The enamel is in this genus, as is well known, rugose and 

 thus of unequal thickness. The coat of cement on the root is 

 comparatively thin and measures on my sections not more 

 than about 0,2 5 mm. In the dentine of the crown a com- 

 paratively thin stratum of »calcigerous cells» is seen below 

 the apical layer of dentine. In the root these cells become 

 more numerous in a layer under the cement which increases 

 towards the end of the root. 



When studied with a low magnifying power it looks as 

 if the side wall of the pulpcavity should have an interiör 

 layer of cement as .welL but if the section is more highly 

 magnified this proves to be a mistake. It is a layer of »calci- 

 gerous cells» or odontoblasts imbedded in a calcified matrix 

 and with numerous branched processes which finally pass 

 över into the dentinal tubes which are directed radially, and 



^ Mikroskopiska vmdersökningar öfver tändernes, särskildt tandbenets, 

 struktur. K. Vet. Akad. Handl. 1836. Stockholm 1837. 

 - Odontography. London 1840 — 45, p. 355. 



