560 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
from the structure and proportions of the limb bones. Biprotodon, by the equable and 
massive development of fore and hind limbs, must have progressed on dry land, like the 
Elephants and Megatherioids, with a regular, quadrupedal, gravigrade pace, though no 
doubt less sluggishly than either Mylodon or Megatherium. It is evident that it could 
not depend on the hind limbs alone for rapid escape from enemies as do the Kangaroos. 
The powerful exertions those singular marsupial animals impose upon their long legs in 
the successive hounds by which they rapidly traverse the plain, call for the provision of 
long muscles and of strongly contracting ones, indicated by the long, strong, three-sided, 
and three-ridged ilia, in which both sides of the prism destined for muscular attachments 
are deeply hollowed. The corresponding pelvic muscles in Biprotodon must have been 
relatively shorter, less thick, but broader, and, in relation to the thigh bone, arranged 
and disposed more or less as in the Elephant. 
Amongst minor differences between Macropus and Biprotodon in the anatomy of a 
part of the skeleton in which they agree in more essential characters, I note that the 
outer margin of the sacral apophyses (Plate XLVII. tig. \,pl i, pi 2 ), uniting with the ilia 
at p,p, do not curve haem ad as in Macropus, making that surface transversely concave. 
The outlet of the anterior canal communicating with the wide intervertebral nerve- 
passage, answering to that marked g in Biprotodon (ib. tig. 2), is relatively smaller and 
more in advance of the soldered zygapophyses uniting together the two sacrals in 
Macropus. The “ spine of the ilium ” in Macropus is represented by a relatively nar- 
rower and less prominent surface than in Biprotodon, is further from the ischial spine, 
nearer the middle of the back wall of the acetabulum in Macropus. The breadth of 
this wall is almost equal in the Great Kangaroo, and the hind contour of the acetabular 
brim is almost parallel with the coextensive inner and hinder border of the innominatum. 
The ischium, as it is produced backward beyond the acetabulum, is relatively more 
compressed and lamelliform in Macropus than in Biprotodon, and, most probably, is 
relatively longer. In the acetabulum itself the vascular groove and the ligamentous 
depression are relatively deeper in Macropus than in Biprotodon. 
§ 9. Femur. — The femur is remarkable for the length, breadth, and depth of the 
proximal end, including the “ head,” “ neck,” and “ trochanters,” for the rise of the head 
above the great trochanter, for the fore-and-aft flattening of the shaft, and for the extent 
in the same direction of the inner condyle chiefly due to the prominence of its narrow 
anterior tuberous end. 
The chief dimensions of this bone are given in the 4 Table of Admeasurements,’ p. 574. 
The “head” (Plates XLYIII. & XLIX. fig. 1, a) is egg-shaped, the great end hemi- 
spherical with the articular surface produced upon the upper part of the neck, contracting 
and representing the small end of the egg (Plate XLVIII. fig. 1, h). There is no pit for 
attachment of a ligamentum teres ; the sole indication of any special addition to the fibres 
of the capsule of the joint is a rough shallow indent of an angular form, encroaching on 
the ball from the under part of its periphery (Plate XLIX. fig. 1, c ). The fore-and-aft 
diameter of the head is 4^ inches ; the transverse extent to the end of the supracervical 
