TEETH OF PHYSETER 21 



I have in a few cases (Text-fig. 12) found an apparent absence 

 of a second outgrowth of the dental lamina. There is here 

 a specially long single outgrowth which is less like a residual 

 lamina than in other teeth, as may be noted by a comparison 

 with Text-fig. 9. Nevertheless, there are some reasons for 

 regarding this outgrowth as the representative of the residual 

 lamina though the usually present additional outgrowth seems 

 to be absent. I beheve, however, that this structure is not 

 absent, but present in the form of a process of epithelium of 

 a somewhat different appearance and origin. Close to the 

 stalk of the dental lamina, and close to its origin from the 

 oesophageal epithelium, is a pyramidal heap of cells which is 

 continuous with the stalk but also arises separately from the 

 oesophageal epithehum. This pyramid has its apex directed 

 upwards, its wider base being continuous with the oesophageal 

 epithehum. It is not large, as I could only find it in one to 

 three continuous sections. I think that this outgrowth may be 

 compared with that which I have described above as existing 

 in most of the teeth of the upper jaw. If this supposition is 

 wrong, I cannot at the moment compare it with anything else, 

 except perhaps as a dwarfed equivalent of the mass of indepen- 

 dent outgrowths which Pouchet and Beauregard have figured 

 as growing from the oesophageal epithelium in the immediate 

 neighbourhood of a tooth germ. 



It should be noted (as is shown in Text-fig. 13) that this 

 pyramidal outgrowth is received into an excavation of the 

 mesoderm tissue surrounding the tooth folhcle, as are other 

 parts of the developing tooth series. It is not, therefore, to 

 be looked upon as merely an outgrowth of the oesophageal 

 epithelium having no relation to a particular tooth germ. 



It is possibly the case that the absence of the basal pyramidal 

 outgrowth of the oesophageal epithelium to which reference 

 has just been made is not always a reality, for in the three 

 consecutive sections in one case (Text-fig. 12) I could find this 

 outgrowth in only one or two sections, and there but small 

 and rather of a rounded than conical form. It may be, there- 

 fore, that this structure has been missed or— if present— not 



