566 ME. M. r, woouwABD oir [Mayo, 



probably would not cut the gum, although at times it may do so 

 (Thomas, 23). 



There is a complete replacement of the lower incisors, but the 

 successors develop at very different times, piTl and plTa maturing 

 long before pT^. Consequently in my fustus no sign of the future 

 1)172 was visible, although the enamel-organs of p[.'i and pITiT were 

 just recognizable. As a matter of fact pi.lj is, 1 believe, the last 

 permanent ante-molar tooth to cut the gum, appearing soon after 

 the eruption of ppm.^. 



The Canines. 



The milk-canines possess single roots, and are but slightly 

 larger than the incisors (tig. 13) ; whereas the permanent canines 

 are very large teeth, with pointed crowns, and each provided with 

 two fangs. 



The Premolars. 



Pm. 1 



^ are said to be present in one dentition only. If this be the 



Piu. 1 

 case these teeth would appear to belong to the milk-dentition, for 

 there is present on the lingual sides of their enamel-organs well- 

 marked continuations of the dental lamina, precisely similar in 

 their relationship to that seen by the side of <lo., whicji gives riwo 

 to the enamel-organ of po., only the inner ends of the former are 

 perhaps a trifle less swollen. It is just possible that these 

 structures may give rise to the enamel-organs of successors at a 

 late period, for the first premolar of the adult skull appears to be 

 a slightly stouter tooth than that of the young animal. 



The lingually situated dental lamina in both the upper and 

 lower jaws gets smaller and more irregular behind pm. 1, but soon 

 becomes definitely swollen, and forms the commencement of an 

 enamel-organ (figs. 11 & 12, ppm.2); this, from its position and 

 backward condition, is evidently that of a successional tooth, viz., 

 ppm. 2. This identification is rendered more certain by finding on 

 the labial side of this structure a small calcified tooth (dpm. 2), 

 devoid of enamel, but possessing a much reduced enamel-organ '. 

 In the case of the upper tooth this reduced enamel-organ is 

 attached to the gum close to, but independent of, the swollen, 

 lingually-situated dental lamina above referred to (ppm. 2). In the 

 lower jaw, liowever, the enamel-organ of the vestigial tooth 

 (fig. 12, dpm.'2) is apparently attached to the corresponding lingual 

 swelling of the dental lamina, thus exhibiting the normal relation- 

 ships of a milk and a replacing tooth. 



The deciduous 2nd premolar is then reduced and early lost, 

 while its succe«iSor is somewhat precociously developed (ef. tig. 11, 



' In a preliminary note, read before tlie British Association, 1895 (27). 

 I stated that there were traces of tive preuiolara in Gymnura : this is not the 

 case ■ tlie error arose through a misinterpretation of a curious development of 

 the pulp of this tooth, dpm. 2 (see PI. XXIV. tig. 11, p), which was mis- 

 taken for a successor. 



