1896.] MAMMALIAN DBNIITIOK. 561 



The Upper Incisors. 



I- 1 & '• 2 are present as functional teeth both in the milk and 

 replacing dentition, but the latter (pi- 1 & pi. 2) develop late, and in 

 my sections are only indicated by vvell-raarifed lingual growths of 

 the dental lamina. Pi- 2 is the most variable in the different 

 species, and in the younger stage examined no signs of it are yet 

 visible. ]^ as a functional tooth is known only in the adult 

 dentition. Leche refers this to the replacing series, because he 

 finds a bud-shaped labial outgrowth of the dental lamina related 

 to the enamel-organ of this tooth. In both my specimens I find 

 a calcified structure connected with this labial growth (fig. 2, cli.3 ) ; 

 this in the younger stage is a distinctly cup-shaped dentinal body, 

 while in the older specimen (fig. 2 a) the condition is more like that 

 figured by Leche (Taf . vii. fig. 52, Jd. 3), save there is a small calci- 

 fication indenting his Jd. 8 from behind. A comparison of this 

 labial calcification (di. 3) with the reduced ^ (fig. 1 a) shows that 

 these two structures evidently belong to the same order, i. e. are 

 reduced teeth of the milk series, the incisior being more vestigial. 



This confirms Leche's view that the adult JJ* belongs to the 

 replacing series, and is the true P'-3 . 



ITie Lower Incisors. 



The first enlargement of the dental lamina in the lower jaw is 

 situated in front of the enamel-organ of the first functional incisor ; 

 it is a very conspicuous structure in the younger stage, being 

 slightly bell-shaped and possessed of a small labial outgrowth 

 (Plate XXTll. fig. 3) ; this evidently corresponds with what Leche 

 believes to be a remnant of the true O (see Taf. ii. figs. 13 & 14), 

 which is here possibly represented both in the raUk and permanent 

 series. 



The second incisor, i. e. the anterior functional one, is a very 

 large and highly differentiated tooth in both specimens, and 

 exhibits a strong lingual growth of the dental lamina, which even- 

 tually forms the enamel-organ of the successor, this tooth 172 being 

 well developed in both dentitions. 



The posterior functional incisor UB is very backward in its 

 development and variable, for it is larger in the younger of the 

 two specimens examined. A long, narrow, cord-like (in section) 

 band of cells grows out from the neck of the enamel-organ of this 

 tooth on its labial side (fig. 4, dTs), being sometimes swollen at its 

 free end and slightly indented ; this evidently represents the last 

 trace of an earlier dentition, and from a comparison with di.3 in 

 the older stage, one is justified in concluding that it represents the 

 enamel-organ of di73 undergoing suppression. 



Between iTa and o. the dental lamina is very strongly developed, 

 and suggests the possible presence of the last trace of one of 

 the missing Marsupial incisors. 



The lower canine is represented by a bell-shaped enamel-organ 

 attached to the buccal epithehum by a well-marked neck of dental 



