208 H. SPENCER HARRISON. 



The anterior palatine tooth is clearly the successional 

 tooth I mentioned in describing my last specimen^ and judg- 

 ing from the space it occupies^ has replaced at least two of 

 the alternating series. Of the latter there are four to five, 

 posterior to which are two of the uniform series, these being 

 no doubt the representatives of the two enamel organs 

 described in my 21'2 cm. specimen. 



The left vomer has a small though well-developed tooth. 



In the mandible the anterior region is beginning to 

 assume the appearance characteristic of the young adult, 

 that is to say, the teeth and bone are becoming related to 

 one another in such a way as to foreshadow the two large 

 anterior " teeth." At this stage the components are clearly 

 two in each case, the anterior being the first successional 

 (fig. 26, t. s. 1), while the posterior is the second successional 

 {t. s. 2). The latter is a very large tooth, and, from comparison 

 of this stage with adult individuals, I have come to the con- 

 clusion that it eventually forms practically the only actual 

 dentinal portion of the adult compound tooth, the remainder 

 consisting of bone. In the body of this paper I have stated 

 that I consider these front teeth to have each three compo- 

 nents. I am now of opinion that there are only two 

 concerned, and that the anterior of these is worn away at 

 a stage very little beyond that we are now considering. The 

 most anterior tooth of fig. 26 is not to be found in the present 

 specimen, and has probably been shed. 



Posterior to the large successional tooth are the remaining 

 members of the alternating series, now only seven in number. 

 Since there were originally sixteen alternating teeth on each 

 side, it is evident that the space formerly occupied by nine 

 teeth is now taken up by two only. From this comparison, 

 and from the space in the jaw occupied by the second suc- 

 cessional, the latter has obviously displaced six or seven of 

 the alternating series. This would at first sight appear to be 

 very contradictory to my view that a tooth of the fourth 

 dentition usually replaces two teeth, one each of the second 

 and third. The conspicuous irregularity in this case is, how- 



