30 ARKIV FÖR ZOOLOGI. BAND 3. :f^:0 3. 



especially if it is made near the base of the tooth, a number 

 of sections of canals irregularly placed and of different size. 

 In the peripheric part of the section the canals are evidently 

 directed towards the periphery. The teeth which already 

 ha ve assumed the columnar shape (as for instance fig. 9 d) 

 have the canals more longitudinally stretched than in the 

 others, but even in them branches, a t least partly loop-shaped, 

 tiirn off from the main longitudinal direction and extend 

 towards the periphery of the tooth; and this is not a singular 

 occurrence but it is the regular structnre of the whole peri- 

 pheric layer of dentine (fig. 10). The central canals divide 

 also pretty of ten in to branches, but these branches are, on 

 the whole, parallel. Considering these facts it is quite appa- 

 rent that the tooth of Orycteropus is a simple unit and not 

 compound of several »denticles» or any other kind of pri- 

 mary elements. Secondarily the teeth developed gradually 

 into such a direction that their structure appears to indicate 

 that they really were compound. This is effected by a spe- 

 cialisation in such a manner that all the different nutritive 

 canals become quite straight and parallel. They cease to 

 branch and a section through one of the molars proves that 

 there are no canals bending towards the periphery, but all 

 of them run parallel with the peripher}^ Avhich has a very 

 thin layer of cement. Round each of the canals a layer of 

 dentine is formed which is more or less regularly prismatic. 

 If only the structure of the molars is studied one might feel 

 tempted to speak of »prisms» of dentine, »denticles» and 

 such, but these things are all of them coenogenetic products. 

 The authors who have interpreted these elements as primary 

 have thus made a mistake and considered the final results 

 of a peciiliar secondary specialisation as remains of a primary 

 and primitive structure. 



A study of the transformation to which the central or 

 main pulp of the single teeth has been subjected, leads to a 

 similar conclusion. As long as the teeth had a limited growth 

 and closed roots the situation of the pulp was about central 

 as in other mammalian teeth with normal structure. A long- 

 itudinal section through the tooth Avhich has been the (origi- 

 nal to fig. 9 a., proves this fully. There is a large central 

 pulp (conf. fig. 11) extending into the small crown and 

 occupying the whole centre of the root the tip of which con- 



