76 
BUiSCKTHElilA. 
CiTvier describes'^' the tibia of Carnivora as follows: “Quant h la tete 
inferieiire, tons les carnassiers se distinguent de I’liomme par sa figure plus 
dtroite du cote externe que le I’interne, et par sa division en deux fosses 
oWique, au moyen d’une arete arrondie qui repond h la poulie de I’astra- 
gale. ... Le phoque I’a cependant d’une forme tres-particuli^;re par 
I’excessif aplatissement de sa moitie supcirieure, et par sa facette particulaire 
inferieiire, qui est en concavite simple et pen profonde.” 
The astragalar articular face of the tibia, in the genera above named, 
is not divided into the two oblique fossm by “a rounded crest which cor¬ 
responds to the groove of the superior pulley-shaped face of the astragalus”. 
It is uninterrupted and more or less oblique in the transverse direction; 
always so at the posterior border. The inner malleolar process is produced 
downward, and rests in a concavity on the inner side of the neck of the 
astragalus. The astragalus, which I have seen in several of the species, 
presents a corresponding trochlear face; that is, instead of a groove, it 
presents an open angle upward, which separates the superior from the 
oblique internal face. The superior plane is flat, but is interrupted on the 
posterior side b}^.a groove. This groove is the posterior extremity of that 
which divides the superior face of the astragalus in- the higher Mammalia^ 
but here it contracts to a point and disappears next the fibular face just as 
it reaches the superior surface. The fibular face is vertical, and shares on 
its posterior part a large ligamentous fossa with the opposed part of the 
fibula. The distal end of the fibula is remarkably stout. 
This structure finds its counterpart in the internal half of the astrag¬ 
alus of the Opossum. The arrangement permits a rotary movement of the 
astragalus, and thus of the whole foot, on the tibia; the fibula, with its 
fixed articulation with the astragulus, rotating on the tibia, as in the Pedi- 
manous MarsujgiaVia. The flatness of the inner malleolus in some of the 
species indicates that the capacity for rotation was less in them than in 
others. This arrangement exactly reverses the extensive oblique fibulo- 
astragalar articulation seen in the Opossum, the Pctaurista., Dasynriis, &c. 
Professor Owen, in describing the astragalus of the Wombat (Phascolomys), 
says: “Tlie upper articular surface for the tibia is, as usual, concavo- 
* Ossemeus Fossiles, vii, p. 122. 
