TEETH OF PHYSETER 



growing tooth is represented us the dental papilla <»nly, growing 

 upwards into a cavity. . 



A rough survey of the series of sections, one of which is 

 shown in Text-tig. 1, shows also that there is apt to be con- 

 siderable difference in size between some of the tooth cavities 

 of the upper jaw and those of the lower. This is not always the 

 case ; but posteriorly (i. e. nearer to the condyle of the jaw) 

 the follicles of the upper jaw teeth are deeper than those of the 

 lower jaw, even twice as deep, in that and other regions. This 

 is correlated with a greater length of the dental lamina, which 

 will now be described. 



It seems to be a general rule — so general that Sir Charles 

 Tomes (6) makes his diagrams of the developing teeth conform 

 to it — that the dental lamina is oblique in direction, running 

 indeed at times almost parallel with the oesophageal epithelium, 

 of which it is a downgrowth. In Physeter, as the figures 

 of Pouchet and Beauregard indeed show, this lamina is 

 absolutely at right angles to the oesophageal epithelium. 

 This will be apparent from an examination of Text-figs. 3 and 4, 

 &c., annexed hereto. The origin of the lamina shows no points 

 of particular interest. It arises from the malpighian stratum, 

 at both sides of an ingrowth of the superficial layer of cells 

 which thus forms its core. 



The histological condition of the material was good enough 

 to show the difference between the central core of the lamina 

 and the often cubical layer of epidermis which surrounds it 

 externally. I do not, however, attempt any special description 

 of the various cells, as they do not seem to present any features 

 of disagreement with those of the developing teeth in other 

 mammals. 



Teeth of the Lower Jaw\ 



My examination of the teeth of the lower jaw was hindered by 

 the condition of the sections of the anterior region of these 

 jaw rami. The tooth follicles upon which I have already com- 

 mented were often entirely empty of contents, the jaws being 

 here obviously more exposed to external injury. I have, how- 



