DEVELOPMENT OP TEKTH IN HATTERIA PUNCTATA. 175 



(fig. 9, jp. lin.), and in others tliey nre quite independent of 

 the latter (fig. 8, man. lin. ; fig. 9, m. lin.). 



In the maxillary region we find that the labial ingrowth 

 appears in sections at or near the middle of an}' one of the 

 posterior teeth, in the form of a more or less lobed projection 

 from the side of the enamel organ (fig. 9, m. lah.). In the 

 space between two teeth it arises independently from the 

 epidermis, and this is also the case opposite the anterior 

 maxillary teeth. Its deepest portion is close to the developing 

 maxilla, and the intervening mesoblast is denser than else- 

 where. The lingual ingrowth appears anteriorly in the form 

 of a simple baud of cells projecting from the sides of the 

 enamel organs, and having here the appearance of a residual 

 dental lamina. Posteriorly it is free from the enamel organs 

 (fig. 9, m. lin.). The alternating character of the maxillary 

 teeth is now expressed chiefly in their sizes. 



The anterior indication of the palatine ingrowths is found 

 as a mass of cells attached to the epidermis, and already un- 

 mistakably glandular in arrangement. These cells can be 

 traced backwards into the labial and lingutil ingrowths, and 

 in the space between these the enamel organs and teeth 

 appear. The relation is, as before, closest between the lingual 

 ingrowth and the enamel organs, and fig. 9, j^- lin., represents 

 the condition for all four palatine teeth. The labial ingrowth 

 is more conspicuous than the lingual, and is throughout 

 independent of the enamel organs. The two fuse posteriorly, 

 and are continued backwards for a little distance as an 

 epidermal groove, as in Stage E. In the maxilla there is a 

 short continuation of the ingrowths posteriorly, free from 

 the epidermis. 



The teeth are well calcified, and have a conspicuous laj'er 

 of t'namel (figs. 8 and 9, en.). The}' are not yet fused with 

 the bone, but are in close proximity to it. 



In the lower jaw the teeth are more advanced than in the 

 upper, and are separated from the bone by a very short 

 interval, especially on the outer side. The line of subsequent 

 union is indicated by a band of mesodermal cells. On each 



