1896.] MAMMALIAN DENTITION. 561 
The Upper Incisors. 
I.1&i.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 well-marked 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. 1.3 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, di.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 de. (fig. 1 a) shows that 
these two structures evidently belong to the same order, 7. ¢. are 
reduced teeth of the milk series, the incisior being more vestigial. 
This confirms Leche’s view that the adult i3 belongs to the 
replacing series, and is the true pi. 3. 
The 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 XXIII. fig.3); this evidently corresponds with what Leche 
believes to be a remnant of the true i. 1 (see Taf. ii. figs. 13 & 14), 
which is here possibly represented both in the milk and permanent 
series. 
The second incisor, 7. ¢. 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 j.2 being 
well developed in both dentitions. 
The posterior functional incisor j.3 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, di.3), 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 di.3 undergoing suppression. 
Between i.3 and ¢. 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 epithelium by a well-marked neck of dental 
