564 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
Macropus further agrees with Diprotodon and differs from JElephas in the continuity 
of the articular surface, giving that of the synovial cavity, of the rotular and condylar 
joints; but in Macropus the inner as well as the outer condyle is so continuous. The 
intercondylar groove is relatively wider in Macropus than in Diprotodon, and, the 
condyles being more backwardly produced, it is deeper. The longitudinal ridge-like 
small trochanter is placed higher in Macropus as in Diprotodon than it is in Elephas. 
The attachment of that muscle, which leaves a circular rough patch at the back of the 
*emoral shaft in Diprotodon , is developed into a tuberosity in Macropus. The trochan- 
terian depression is very deep in Macropus as it is in Diprotodon. The great trochanter 
is bilobed exteriorly in Macropus , but with a deeper and differently directed dividing- 
channel than in Diprotodon. 
I discern in the foregoing correspondences the essential marks of affinity, and view 
the greater elevation of the trochanter major in Macropus , the greater length and cylin- 
droid form of the shaft of the femur, the greater relative antero-posterior extent of the 
distal end, and especially of the outer condyle, with the stronger indications of muscular 
attachment, as adaptive characters in the smaller Marsupial related to its more rapid and 
vigorous modes of locomotion. 
§ 10. Tibia. — The tibia, of the general dimensions given in the Table of Admeasure- 
ments, p. 574. I conclude, by the agreement in size and character of the upper articular 
surface (Plate XLIX. fig. 4) with the lower one of the femur (Plate XLVIII. fig. 4), to 
belong to the same leg, viz. the right one, of Diprotodon. 
The external upper articular surface (Plate XLIX. figs. 3 & 4, a) is gently undulated, 
with a transverse convexity adapted to the corresponding concavity on the outer femoral 
condyle, and with the concavities, though slight, answering to the convexities of that 
condyle. The inner articular surface (ib. fig. 4, b) is larger, and presents a uniform con- 
cavity to the convex inner femoral condyle. The ridge or spine (ib. figs. 2, 4, c) between the 
articular surfaces extends 2 inches from behind forward and a little outward ; it is from 
6 lines to 10 lines thick, and is roughly excavated above. The rough part of the upper 
surface of the tibia (ib. d), in advance of the articulations, is more extended transversely 
from behind forward. The breadth of the upper surface exceeds by two-fifths the fore- 
and-aft diameter. The articular surface for the head of the fibula (ib. fig. 3, e) is con- 
tinuous with the outer articular surface ( a ), and extends from its outer and hinder 
margin at a rather acute angle or nearly a right angle, 1 inch 4 lines down the shaft, 
the breadth of the surface being 1 inch 6 lines. In advance of this surface proj ects the 
external tuberosity (/), from which a thick (epicnemial) ridge-like rising of bone (ib. 
fig. 2, g, g) extends in front of the upper end of the tibia for about 5^ inches. This 
ridge or prominent tract is longitudinally striate or scratched, as if it were an ossified 
ligamentous attachment. At the middle of the fore part of the tibial head a narrow 
ridge (ib. fig. 2, h) is continued from the transverse one 2 inches down the shaft, like 
the procnemial ridge in birds, but much less produced. From the junction of the 
“ epicnemial ” ridge with the outer tuberosity a narrow “ ectocnemial ” ridge (ib. i) 
