196 H. SPENCER HARRISON. 



step in the dentigerous edge of the bone, and on this higher 

 level are the much worn members of the original alternating 

 series. The first three on the one side, and two on the 

 other, judging by the space occupied by a smooth ridge, are 

 worn down to the bone, and posterior to this are four teeth 

 in each case alternating in size. Allowing each successional 

 tooth to equal two of the original set, and including the 

 teeth that are obviously worn away, the totals are thirteen 

 and fourteen respectively. The relationships are not always 

 so simple as this, but I believe it will be found that tooth 

 change is confined to the anterior third of the jaw, the first 

 four maxillary teeth being usually successional. This skull 

 has on the two maxillse respectively four and five teeth of 

 the uniform series. My remarks on the subject of the con- 

 tinuance of tooth change in the premaxiliee during further 

 growth will also apply to the maxilla. It is possible, though 

 not probable, that successional teeth are formed further back 

 than I have described, but at my latest stage there is no 

 independent residual dental lamina in the middle region of 

 the maxilla. This ai'gument, however, in the case of Hatteria 

 has little weight in view of what we have seen in other 

 regions, where the dental epidermal ingrowth may remain 

 latent, as it were, in the face of the internal groove which is 

 attached to the teeth. 



The right palatine of the same adult specimen has a large 

 anterior tooth, showing the same indications of its succes- 

 sional nature as do the first three or four maxillary. The left 

 palatine, on the other hand, terminates in a slightly sinuate 

 ridge. The successional tooth of the right side no doubt 

 corresponds with the one shown in fig. 28, and has replaced 

 Nos. 1 and 2 in ordero In another adult skull I find that the 

 large anterior palatine tooth is present on both sides. It is an 

 interesting example of the greater variability of the palatine 

 dentition, that whereas in the first of the adult skulls I have 

 described the proportion of uniform teeth in maxilla and 

 palatine respectively is 5 : 7, in the other it is 6 : 5. I be- 

 lieve that the tooth-change in the palatine will be found to 



