2 FRANK E. BEDDARD 



able to set forth here, certain pecuHarities in the growth of the 

 teeth of Physeter macrocephalus are worth confirma- 

 tion, though I doubt whether I am able to settle definitely the 

 question of the homologies of the teeth of the adult, whether — 

 that is to say — they belong to the milk or permanent dentition. 

 The former view of the odontocyte dentition seems to be the 

 one generally held ; but by others the question is considered 

 to be still open. It should be added, however, that these views 

 are not at all based upon a consideration of the facts described 

 by Pouchet and Beauregard, whose memoir has been largely 

 overlooked. This is a further reason for again directing the 

 attention of zoologists to this subject. 



I may commence by directing attention to a matter not 

 illustrated in the figures of the teeth published by Messrs. 

 Pouchet and Beauregard ; this is the position of the teeth of 

 the upper and lower jaw with reference to each other. It will 

 be seen by an inspection of Text-fig. 1 that the teeth of the 

 upper jaw are divided from each other by a space that is less 

 than the space dividing the two teeth rows of the lower jaw — 

 that is to say, the upper teeth are distinctly within the lower 

 teeth. Furthermore, the upper teeth are quite vertical in 

 position, and at right angles with the longitudinal axis of the 

 head, while the two rows of teeth in the lower jaw are at an 

 angle to each other, and to the same axis of the head. Thus the 

 teeth of the lower jaw look outwards as well as upwards, 

 while those of the upper jaw are directed downwards only. 

 This state of affairs is more marked in the anterior region of the 

 lower jaw. It is due to the varying contour of the lower jaw, 

 which anteriorly is more rounded while posteriorly the upper 

 surface is straighter. Thus the teeth are, so to speak, carried on 

 to what is largely the lateral surface. 



This figure also shows a character which is to be seen more 

 in detail in su])sequent illustrations of the teeth of this foetus. 

 The cavity in which the tooth rudiments lie is not at all invaded 

 by the upgrowth from below forming the dental papilla, which 

 is only represented in this stage by a thickening of the meso- 

 dermic tissue sliown by a closer approximation of the nuclei 



