92 REPORT—1848. 
m4—the last true molar—comes into place, and in Macropus gigas the premolar is 
simultaneously shed. 
Thus four individuals of the great kangaroo may be found to have the same nume- 
rical molar series, viz. m = and yet not any of them have the same or homologous 
teeth. The four grinders, for example, may be— 
d3,d4,m1,m2; or 
d4,m1,m2,m3; or 
pil,m1,m2,m3; or 
m1, m 2,m 3, m 4. 
Prof. Owen, not having traced out when he published his ‘Odontography’ all this 
complex interchange and alternating sequence of the dentition of the kangaroo, had 
been compelled to postpone any definition of the deciduous formula until all the 
stages had been observed. The order described was not that followed in some of the 
smaller kangaroos. In Macropus Bonetti, e. g. the acquisition of m3 is not accom- 
panied by the shedding of d3: a skull of that species 5 in. in length, hadm = being 
d3, d4, m1, m2, and m3: both milk molars are shed and replaced by the single 
premolar p4, but this tooth is not pushed out by the rising into place of the last 
molar, m4: hence the mature dentition shows five grinders on each side, or 
Pr m — . Thus the total number of molar teeth developed in the kangaroos 
is 28, consisting of 2 deciduous molars, 1 premolar and 4 permanent molars on each 
side of both jaws. The deciduous molars were the homologues of those in the 
human subject, viz. d m3 and 4; the premolar is the homologue of the second 
bicuspid, or p4; the three anterior molars answer to the three true or tuberculate 
molars in man, viz. m1, 2 and 3: the fourth molar in the kangaroo is a supernu- 
merary tooth. 
After describing other particulars in which the proposed notation for the indivi- 
dual teeth was exemplified, Prof. Owen proceeded to observe, that the substitution 
of signs for verbal descriptions was at once the power of the algebraist and the proof 
of the exactness of mathematical reasoning. To gain the like power for anatomical 
science should be the chief aim of its cultivators; to this end the determination of 
the homologies of parts was the indispensable step which should be followed by de-- 
noting the part by a symbol representing it under all its modifications of form and 
in all the species of animals in which such part existed. 
As an example of the amount of information which might thereby be conveyed in 
a small compass, several illustrations were given, amongst which were the follow- 
ing :—The permanent dentition of the Anoplotherium was— 
p23 gual 4—4 Oars 44 
ar A TH Pony | 
This was stated to be an example of the typical series of teeth in the placental mam- 
malia with true premolars. The deciduous dentition of the Anoplotherium was-— 
as = in — = 32: dm1 was succeeded by p1, dm2 by p2, dm3 by 
p3, dm4 by p4: but m1 was in place before dm1 was shed; m 2 was coincident 
with p1 and p2; next came m3 and p 3; and then, coincidently, p4 and m3. 
—3 1-1 3-3  3-3_ 
5-3. 1—1 ares 
its deciduous, dentition is 7 a —> m = = 32: dm 1 is not succeeded by 
p 1; the other three dmm are succeeded by teeth which answer to p2,p3 and p4 
of the Anoplotherium. 
The permanent dentition of the horse was i 40: 
ye 
ae 
4 3—3 ‘ 
a but only dm 5—,' p 1 is not 
In the dog, on the other hand, there are p 
