576 
PROFESSOR OWEN ON THE AFFINITIES OF THYLACOLEO. 
of which it seems necessary to add to former figures the palatal view only for com¬ 
parison with fig. 3 of Plate 11 (Paper of 18 71). 
The foremost tooth (Plate 39, fig. 1 , i i) shows an exserted crown, 1 inch 3 lines in 
length, curved with the convexity forward, subcompressed, conical, pointed, obtuse 
anteriorly, trenchant behind where the enamel forms a finely serrate ridge; it is in 
shape and size a tooth suggestive of powers of penetration and prehension. It is deeply 
inserted by a stout cement-clad fang, indicative of limited growth. The entire length 
of the tooth, following the curve, is 2| inches. 
The second tooth, (ib., ib., i 2 ) projects behind and partly mesiad of the base of the 
first, its crown is but 5 lines in length ; other dimensions are shown in the figure, 
The working surface is bevelled off, before and behind, to a low ridge. 
Next to this tooth and partially overlapping the hind and outer part of its crown 
is that of a larger trenchant tooth, i 3, 7 lines in longitudinal, 5 lines in transverse 
diameters, but barely exceeding the second tooth in height. 
This is followed by a fourth, p 1 , about the size of the second, i 2 . Its crown is 
partly overlapped by the larger tooth, is; it is also subtrencliant lengthwise. 
External to the hinder part of p 1 , and about half the size, projects the crown of a 
tubercular tooth, p 2 ; it is immediately followed by a sixth tooth, p 3, of similar 
shape and size. This tooth is partly overlapped externally by the fore end of the 
great carnassial tooth, p 4. 
The homologies indicated by the symbols of the five teeth crowded between i 1 and 
p 4 may be questioned, but that of the latter with the trenchant premolar in existing 
phytophagous Diprotodonts is plain. In plate 100, pop. 381-394 of the undercited 
work,* the eight chief modifications of the comparable Diprotodont dentition in existing 
Marsupials are described and figured. Of these the genera Hypsiprymnus and 
Phascolarctos offer the nearest approach to Thylacoleo in the proportions of antero¬ 
posterior to vertical extent of the crown of p 4. But the size of this tooth in those 
existing genera is much less relatively to the other teeth, especially to the bruising 
molars, four on each side of the upper, as of the lower jaw, which in them follow the 
trenchant premolar. In those genera, as in Macropus , Petaurus and Phalangistci, 
three close-set incisors are lodged in the premaxillary ; and, in Mctcropus, the third 
incisor is as much larger than the second, as is the third tooth (Plate 39, fig. 1 , i s) in 
the series of upper teeth in Thylacoleo. 
In Phascolarctos and Hypsiprymnus a minute canine projects from the maxillo- 
premaxillary suture with a well-marked interval between the incisors in front and the 
trenchant premolar behind. In Petaurus and Phalangistci Cookii two small premolars, 
p 3, p 2, precede the tooth p 4, which is in contact with the foremost of the four 
crushing molars. 
With the five teeth, therefore, preceding the trenchant premolar, in the above-cited 
existing Diprotodonts may be homologized, in the aggregate, the five teeth between 
* ‘ Odontography,’ 8vo., 1840. 
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