DEVELOPMENT OF TEETH IN HATTERIA PUNCTATA. 181 



lies in the premaxillary teeth (figs. 17 and 20). Here we find 

 that the second tooth has remained of about the same size as 

 at Stage S, whilst the 6rst has grown considerably. The 

 third is still the largest. A stained and mounted preparation 

 of the premaxilla shows that No. 2 is evidently about to be 

 shedj and that there has been a large absorption of bone at 

 its base internally. From the evidence of sections of this 

 stage (see below), there was no doubt a successional tooth at 

 this point, unfortunately removed in making the preparation 

 (fig. 20). 



In the lower jaw the teeth have increased to sixteen on 

 each side. The alteration in size is fairly regular, except in 

 the case of the first five teeth. There is a short gap ante- 

 riorly between the teeth of the two sides over the mandibular 

 symphysis. 



Sagittal sections of the premaxilla of another individual 

 of this stage show that the labio-dental groove has been 

 formed ; the internal dental fossa is not typically developed 

 in this region (fig. 18). From the deepest portion of the 

 epithelium of the internal fossa a dental lamina projects into 

 the mesoderm. This is found in the whole premaxillary 

 region, and opposite the second functional tooth it bears a 

 well-developed enamel organ with a calcified tooth (fig. 18, 

 t. s. 1). A similar condition of the dental lamina is found in 

 the lower jaw at this stage (fig. 19, r. d. I.), but there are 

 at present no signs of successional teeth. The second pre- 

 maxillary is shoAvn to be separated from the inner table of 

 the bone, absorption having taken place at the base of the 

 tooth. In some sections a portion of bone is seen to be still 

 attached to the latter, and is probably cast away with it, 

 perhaps representing what Tomes {' Manual of Dental Ana- 

 tomy ') calls " bone of attachment.'^ On the labial side also 

 bone absorption has commenced. As is seen in fig*. 20 the 

 absorption on the lingual side extends to the bases of the 

 first and third teeth, and in addition, sections show that 

 there is a separate small area of absorption at the base of 

 the third. I shall prove later that each of these three teeth 



