328 PROF. OWEN ON THE CLASSIFICATION 
anterior ones not being produced beyond that line as in the Hypsiprymni; the third or 
external incisor is also broader in the Kangaroos, and is grooved and complicated by one 
or two folds of the enamel continued from the outer side of the tooth obliquely forwards 
and inwards, into the substance of the tooth. In most species the anterior fold is re- 
presented by a simple groove ; the relative size of the outer incisor, the extent and po- 
sition of the posterior fold of enamel, and consequently the proportions of the part of 
the tooth in front or behind it, vary more or less in every species of Macropus: there are 
two folds of enamel near the anterior part of the tooth in Macr. major ; the posterior 
portion is of the greatest extent, and the entire crown of the tooth is relatively broadest 
in this species. The middle incisor is here also complicated with a posterior notch and 
an external groove. These modifications of the external incisors have been pointed out 
in detail by M. Jourdan ; and subgeneric distinctions have been subsequently based upon 
them, but they possess neither sufficient constancy nor physiological consequence, to 
justify such an application. M. Fr. Cuvier has proposed a binary division of the genus 
Macropus as here defined, founded on the absence of permanent spurious molars’ and 
a supposed difference in the mode of succession of the true molars in certain species 
of Kangaroo, combined with modifications of the muzzle or upper lip, and of the tail. 
The dental formula which I have assigned to the genus Macropus is restricted by that 
naturalist in its application to some small species of Kangaroo, grouped together under 
the term Halmaturus, originally applied by Illiger to the Kangaroos generally. The rest 
of the Kangaroos, under the generic term Macropus, are characterized by the following 
ae 6 4—4 
dental formula :—incisors = ; molars 7 aarp 24. 
The truth, however, is, that both the Halmaturi and Macropi of Fr. Cuvier, have their 
teeth developed in precisely the same number and manner ; they only differ in the length 
of time during which certain of these teeth are retained. In the great Kangaroo, for ex- 
ample, the permanent spurious molar which succeeds the corresponding deciduous one 
in the vertical direction, is pushed out of place and shed by the time the last true molar 
has cut the gum: the succeeding true molar is soon afterwards extruded; and I have 
seen a skull of an old Macropus major in the Museum at Leyden, in which the grinders 
were reduced to two on each side of each jaw by this yielding of the anterior ones to the 
vis a tergo of their successors. 
1 M. Fr. Cuvier was aware that a deciduous spurious molar existed in the great Kangaroo and other species 
of his subgenus Macropus, but he believed that it was peculiar to an early period of life, and then existed only 
in a rudimental state or ‘en germe,’ and that instead of being displaced and succeeded in the vertical direction 
by a permanent spurious molar, as in the Halmaturi, it was displaced by the true molars, which are developed 
from behind forwards. I have however detected the crown of the permanent spurious molar in the jaws of the 
Macropus major in a concealed alveolus, and have observed it completely formed and in place in an individual 
which had nearly attained its full size. See F. Cuvier’s account of the Halmaturus Thetis in the ‘ Histoire des 
Mammiferes,’ folio. 
