560 



PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



from the structure and proportions of the limb bones. Diprotodon, by the equable and 

 massive development of fore and hind limbs, must have progressed on dryland, 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 bounds 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 Avliich 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. fig. l,pl i, pi 2), uniting with the ilia 

 a,t p,p, do not curve hsemad 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 (/ in Biprotodon (ib. fig. 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 Macrojms 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 ' Table of Admeasurements,' p. 574. 



The "head" (Plates XLVIII. & 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 tlie small end of the egg (Plate XLVIII. fig. 1, b). 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. ], c). The fore-and-aft 

 diameter of the head is 4^ inches ; the transverse extent to the end of the supracervical 



