580 
PROFESSOR OWEN ON THE AFFINITIES OF THYLACOLEO. 
lateral borders of the base of a bony sheath (fig. 6, b), which overarches the proximal 
three-fourths of the claw-bearing’ part (c) : this sheath is also continued from the sides 
of the broad, somewhat flattened under portion of the articular division of the phalanx, 
which terminates (fig. 8, cl) where the compressed claw extends freely forward. The 
under surface (fig. 7) of the sheath-supporting division of the phalanx is perforated by 
a pair of canals, which transmitted the blood-vessels and nerves to the formative and 
reproductive organ of the talon. 
I have not found any instance of such sheath claw=plialanx in the existing or extinct 
kinds of diprotodont .Marsupials, other than Thylacoleo. 
The placental Mammals which possess such claw-sheath are amongst the carnivorous, 
and, most conspicuously, the Feline species; also certain Edentates, more especially the 
great extinct Megatherioids. 
The chief difference, in these placentals, is that the articular surface, in Felines, 
ends nearer the lower or palmar surface of the joint, which is overtopped by the pro¬ 
minence for insertion of the retractor tendon of the claw ; while in Edentates the 
articular surface leaves a larger proportion of the under part of the base of the phalanx 
free and tuberous for insertion of the powerful muscles which deflect the claw.* In 
all Edentates the claw-bearing part of the slieathed-phalanx is relatively longer, 
thicker, and commonly less acute than in Felines. 
In this comparison the ungual phalanx of Thylacoleo much more closely resembles 
that of Fel is Leo or Fells Tigris .f 
Mandible of Thylacoleo.—I finally submit a description and figures (Plate 41) of 
the fossil mandible with the Tliylacoleon dentition, as the osseous evidence testifying 
most directly to the matter at issue. 
Plate 41, fig. 1, gives the outside view of a mandible of Thylacoleo carnifex, in 
which a carnivorous modification of the dentition has been engrafted, as in the older 
extinct form Plagiaulax (ib., fig. 5), on a Marsupial and Diprotodont type. 
In comparison with the mandible of the Koala ( Phascolarctos , Plate 41, fig. 3) and 
Potoroo (Hypsiprymnus) , which are selected by Professor Flower, F.R.S.,j as most 
nearly resembling that of Thylacoleo, may, first, be noted in Thylacoleo , fig. 1, the 
relative shortness of the dentigerous part of the mandible to its depth, especially at the 
fore end, and the outs welling wall of the socket of the great carnassial premolar (ib., 
* ‘ Memoir on tlie Megatherium,’ 4to., 1860, plate 25, fig. 1, iii.; and ‘ Memoir on the Mylodon,’ 4to., 
1840, plates 15 and 17. 
f The following is Cttviee’s description of this phalanx in the Feline family:—“ La figure de cette 
phalange est celle d’un crochet fait des deux parties: l’une dirigee en avant, courbee, tranchaute et 
pointue, re 90 it l’ongle, dont la forme est a peu pres la meme: la base de cette premiere portion fait une 
espece de capuchon osseux, dans lequel est regue la base de l’ongle comme dans une game.” ‘ Lemons 
d’Anatomie comparee,’ 8 vo., ed. 1835, tome i, p. 434 : “ Les dernieres phalanges dans la famille des 
Chats. ,, It is equally applicable to the subjects of figures 6 and 8 in Plate 40. 
X “ On the Affinities and probable Habits of the extinct Australian Marsupial, Thylacoleo carnifex, 
Owen,” Quarterly Journal of the Geological Society of London, March, 1868, vol. xxiv., p. 307. 
