TOOTH-GERMS IN A WALLABY. 



935 



of a predecessor (PL XLYII. figs. 2 & 3). The importance of 

 this will he discussed later. The last tooth of the series (L) is 

 uiicalcified and at an earUer stage of development than the 

 maxillary teeth in front of it. It lies much nearer to the alveolar 

 margin than do the others, and there is this further point of 

 interest, that the antei'ior end of this tooth overlaps superficially 

 the posterior end of the tooth in front, which is distinctly not the 

 case with the more anteriorly situated teeth. 



According to our identification we recognise at this stage six 

 incisors, one canine and five maxillary teeth. 



LoiverJaw. — The difficulty of interpreting the appearances in the 

 region of the mandibular symphysis is even greater than in the 

 earlier stage. The enormous development of the lower functional 

 incisor, extending as it does through thirty slides*, has disarranged 

 all the parts, more particularly anteriorly where the tip of the 

 tooth becomes more superficial and where it now reaches well in 

 front of the point at which its young enamel organ connected with 

 the oral epithelium. 



Text fig. 188. 





Section showing involution of the oval epithelium 

 at the mandibular symphysis. 



At the symphysis the oral epithelium is turned inwards in the 

 middle line so as to partially cover the opposing ends of the 

 mandibular rami. At this point there is a definite involution 

 of the epithelium into the subjacent tissues. The section being 

 cut at this point in a plane parallel with the anterior surface, the 



* A rough estimate ma}"^ be obtained by stating that a slide carries an average 

 gf twelve sections, each section being yjg mm. in thickness. 



64* 



