LÖNNBERG, THE DENTITION OF DELPHTNAPTERUS LEUCAS. 17 



dentine of the root. The pulpcavity in this comparatively 

 not very old tooth is large, and there is no ossified pulp^ the 

 dentinal tubes radiating straight away from the surface of 

 the pulpcavity. At the tip of the tooth several dentinal tubes 

 can be seen penetrating into the enamel layer. 



With regard to their outer shape 

 the teeth of the Black whale are 

 more stout than those of the two 

 foregoing species. The root is as a 

 rule more or less compressed and 

 often a longitudinal furrow is found 

 along the side which has quite such 

 a situation and appearance as if it 

 was the last trace of a division in 

 two roots and it does not seem im- 

 probable that this really is the case. 



In spite of the different shape 

 of the teeth of the Porpoise (Pho- 

 coena) with their spade-like crowns 

 and cylindrical roots their structure 

 is essen tially the same as in the 

 Dolphin. The crown consists of den- 

 tine and is surrounded by an enamel 

 cowering which has a thickness on 

 my sections of O, i62 mm. The ena- 

 mel covering ends rather abruptly at 

 the base of the crown and then there 

 is a gap before the coat of cement 

 which surrounds the cylindrical root 

 puts in appearance. The cement 

 increases in thickness basally but it 

 is everywhere rather thin and does 

 not attain even the thickness of the 

 enamel. The greatest diameter of 



the cement layer, which I have measured on my sections, is 

 only about one tenth of a millimetre. 



The correspondence in structure between the teeth of 

 the four species now described proves that they all have been 

 developed in a similar way. It proves also that with regard 

 to the microscopical structure and the arrangement and mu- 

 tual relationship of the three different tissues (enamel, den- 



Arkiv för zoologi. Band 7. N:o 2. 2 



Fig. 7. Longitudinal sec- 

 tion through a tooth of Glo- 

 bicephalus melas. e enamel, 

 d dentine, c cement- 



