188 H. SPENCKR HARRISON. 



orfoiu-of the uniform series. We see, then, that, whereas in 

 the maxilla the uniform series of teeth has not yet commenced 

 its development, and is represented by two early enamel 

 organs in the palatine, the teeth are already being rapidly 

 produced in the mandible as the jaws lengthen, ^riie only 

 evidence of the cessation of tooth formation in the mandible 

 was found at Stage T (see p. 180), when there were sixteen 

 teeth of the alternating series, followed posteriorly by one 

 early enamel organ. Stated briefly, then, the position is as 

 follows : — at a stage (differing secondarily, as I believe, in 

 point of time) in the dentition of the three bones under 

 consideration, when the mandible and maxilla have in the 

 alternating series about sixteen teeth each and the palatine 

 sis or seven, there is a more or less prolonged cessation of 

 tooth development, this being longest in the maxilla, shortest 

 in the mandible, and intermediate in the palatine. Up to 

 this stage the teeth have shown the alternation in size so 

 often mentioned here, this characteristic being least marked 

 in the palatine. After this period of inactivity, there is a 

 renewed formation of teeth from behind forwards,^ com- 

 mencing earliest in the mandible, latest in the maxilla, and 

 continuing during the whole period of growth of the animal. 

 I shall attempt to explain these facts in the next section. 



There remain to be discussed a few points of special 

 interest with regard to the succession of teeth. In my 

 description of Stage R, 1 put forward the view that the 

 smaller teeth of the alternating series represent an earlier set 

 than the larger. The evidence for this Avas more conclusive 

 in the upper jaw and in the anterior part of the lower than in 

 the posterior part of the latter, where, in my specimens, size 

 alone suggested any difference in the nature of the teeth. I 

 also found that the second palatine gave marked indications 

 of belonging to the earlier dentition. The mandibular alterna- 



' The posterior teetli of the alternating series are also, as we Jiave seen, 

 formed ou backward prolongations of tJie dental laniiiise. In the case of this 

 series, however, there is no cessation of tooth formation until the set is com- 

 ulete. 



