a 
— 
1896.] MAMMALIAN DENTITION. 577 
successional teeth, shows conclusively to my mind that the first’ 
premolar is present as a calcified tooth in one dentition only, viz., 
a dpm. 1 
in the milk-dentition ; the milk-tooth Gane 1 
persisting in the adult along with the permanent teeth, a slight 
trace only of its successor being visible at a very early stage and 
only for a short period. 
I must furtber conclude that the teeth figured by Bate as 
' . fl 
—S e have no existence, his ppm 
pin. 1 ppm. 1 
teeth. 
I can only imagine that Bate was misled by the presence of the 
small needle-like teeth seen in connection with all the other ante- 
molars into the belief that he had lost a similar one in connection 
: pm. 1 
with ei 
Leche, while accepting Bate’s account, which he was bound to 
do from the limited material at his disposal, states that pm. 1 was 
much more backward than the other milk-teeth, for while the 
latter had well differentiated enamel-organs, that belonging to 
pm. 1 was still club-shaped or only slightly advanced. Thus his 
specimens form with mine a perfect series, which together show 
that at no time is there more than one representative of pm. 1 
differentiated as a tooth, 2. e. dpm. 1, and only fora short period is 
there any indication of ppm. 1. 
) being very large and 
being in reality persistent milk- 
during dissection. 
General Consideration of the Homology of Pm. 1. 
Although there is undoubtedly but one calcified representative 
of pm. 1 present in the Mole, it is possible that some may be 
inclined to regard that tooth as belonging to the permanent rather 
than to the milk series; in that case the lingual growth of the 
dental lamina would have to be regarded as the representative of 
the post-permanent series, similar to that seen in connection with 
the permanent incisors and canines (fig. 28, pe. d/.). Such an 
interpretation has been adopted by Tims (24) for pm. 1 of the Dog 
and Pig’, this author further stating his belief that in those cases 
(Hyrax, &c.) in which pm. 1 is duplicated, the two teeth repre- 
sent the permanent and post-permanent series, and not the milk 
and permanent sets as one might suppose them to do. Against 
this possible interpretation of pm. 1 in the Mole may be urged in 
1 With regard to Tims’s description of the 1st premolar of the Pig, in which 
he figures traces of three dentitions, I believe that there has been a mistake in the 
identification of the teeth, for which I am partially responsible, the sections and 
rough identification of the teeth being mine. On making a fresh and more care- 
ful examination of the sections, and comparing them with an older specimen, 
I find a very backward tooth-germ present between the canine and the supposed 
Ist premolar: this backward germ I take to be the true pm. 1, the tooth 
figured by Tims being dpm. 2; in that case the enormous development and 
swollen nature of the lingual growth of the dental lamina is accounted for, it 
being the germ of ppm. 2, while the labial growth must represent a trace of the 
pre-milk dentition. 
