564 



PKOFESSOE OWEN ON THE EOSSIL MAMMALS OF AUSTKALIA. 



Macropus further agrees with Biprotodon and differs from Elephas 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 Biprotodon, and, the 

 condyles being more backwardly produced, it is deeper. The longitudinal ridge-like 

 small trochanter is placed higher in Macropus as in Biprotodon than it is in Elephas. 

 The attachment of that muscle, which leaves a circular rough patch at the back of the 

 Amoral shaft in Biprotodon, is developed into a tuberosity in Macropus. The trochan- 

 terian depression is very deep in Macropus as it is in Biprotodon. The great trochanter 

 is bilobed exteriorly in Macropus, but with a deeper and differently directed dividing 

 channel than in Biprotodon. 



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 Biprotodon. 



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, h) is larger, and presents a uniform con- 

 cavity to the convex inner femoral condyle. The ridge or sj)ine (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 («), 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 {f), from which a thick (epicnemial) ridge-like rising of bone (ib. 

 fig. 2, g, fj) 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) 



