24 PRANK E. BEDDARD 



least and generally two such outgrowths in the teeth of the 

 upper jaw. The most anterior of these (i. e. that closest to the 

 persisting tooth rudiment) is to be regarded as the residual 

 lamina which is alone (?) met with in the teeth of the lower jaw. 

 Whether I am right or not in regarding the second outgrowth 

 as a milk rudiment, it is at least a point of difference between 

 these teeth and those of the lower jaw, where it appears to be 

 non-existent — at any rate in the embryo which I have 

 examined. 



This again may be a matter of age. As to the residual lamina 

 its exact likeness to that of the lower teeth is not absolute. 

 There is this important difference. While in the case of the 

 lower teeth the lamina is a lamina continuous from section 

 to section, it is not so with the upper teeth ; here in fact the 

 small process (see Text-fig. 10) which may be its equivalent 

 disappears and reappears every two or three sections, thus 

 indicating a series of processes and not a continuous lamina 

 (cf. Text-figs. 9, 10). There is next to be seen a difference — 

 perhaps more apparent than real — between the mode of origin 

 of what I regard as the permanent tooth in the upper and 

 lower jaws. 



As has been already mentioned, the tooth germ in both arises 

 as a thickening of the end of the dental lamina, which is con- 

 tinuous as a thickened edge to that lamina. In examining the 

 whole series of teeth rudiments in the lower jaw, from their 

 commencement at the condylar end of the jaw, the following 

 stages may be detected. The oval thickening, shown in 

 Text-fig. 5, persists in section after section, but gradually 

 alters its shape to a more triangular outline, and at the pointed 

 end away from the origin of the dental lamina the residual 

 lamina gets gradually to be free, the rest of the thickening 

 remaining behind, so to speak, as the actual tooth germ. 



In the upper jaw the series of events is rather different. The 

 same thickened edge appears at first, but its stalk grows 

 longer until a racket-like structure is produced, as shown in 

 Text-fig. 6. Instead of remaining as it is — as is the case with 

 the lower jaw teeth — it is bent over lingually, and the residual 



