TEETH OF PHYSBTER 19 



Woodward (9, PI. xxlvii, figs. 25 a and h) to similar out- 

 growths, which (in Petrogale) the latter regarded simply 

 as tooth germs. Wilson and Hill, however, find that these 

 outgrowths (in Perameles it must be remembered, not 

 Petrogale) are really sheets arising from the dental lamina, 

 and not to be confused with dental rudiments. They refer 

 them to the ' labio-alveolar lamina ' and trace them back in 

 their origin to the oesophageal epithelium, finding sometimes 

 no connexion at all with the dental lamina. I do not attempt 

 to criticize, and content myself with the briefest account 

 of this view of the labial outgrowths in question. I am con- 

 vinced, however, that the structures which I describe here in 

 Physeter macrooephalus really originate from the 

 dental lamina, and are limited to narrow outgrowths like 

 tooth germs. They are not to be seen throughout a long series 

 of continuous sections ; but only in three or four consecutive 

 sections. I have dwelt upon their resemblance to the undoubted 

 tooth germs in this cetacean ; indeed, the only difiiculty in 

 the way of regarding them as tooth germs might be considered 

 to be their origin from the labial instead of from the lingual 

 side of the dental lamina. But in the first place these rudiments 

 do occasionally originate from the lingual side, as I presume 

 from the figures of Pouchet and Beauregard ; and in the second 

 place in a vertically developed dental lamina the actual side 

 of origin seems less important than in an obliquely disposed 

 dental lamina. 



Woodward also found no difficulty in referring such out- 

 growths to a milk dentition, while in the case of the incisors 

 he referred a lingual outgrowth to the permanent series. 

 This position as to the nature of a particular rudimentary 

 tooth is accepted and asserted by Tomes, who writes (6, p. 356) : 

 ' we are justified in saying that any additional specialization of 

 the dental lamina which is situated on the lingual side of 

 a formed germ belongs to a later generation of teeth, and con- 

 versely that any similar outgrowth of the lamina which lies 

 on the labial side of a formed tooth germ belongs to an ante- 

 cedent generation.' But it would, as I think, be pushing this 



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