PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 563 



The femur, like the pelvds, of Biprotodon presents the greatest resemblance in general 

 form and characters to the corresponding bone in Proboscidia. The head is devoid of 

 the ligamentous pit ; the shaft is straight and antero-posteriorly compressed ; there is 

 little* or no medullary cavity. 



Passing to particulars of structure, there appear several more or less well-marked 

 differences. 



The head rises higher above the neck and trochanter in ElepJias ; it has a more directly 

 upward aspect, the neck is shorter, the great trochanter is absolutely, as well as rela- 

 tively, of less extent in Elephas. The trochanterian depression is less deep, and opens 

 nearer the exterior surface of the trochanter. A ridge is continued downward from the 

 border of the depression, which, with a second ridge continued downward from the outer 

 part of the trochanter, bounds a flat facet forming the outer surface of the upper half 

 of the shaft : there is no such definite facet in Biprotodon. At the upper and fore part 

 of the trochanter in Elephas there projects a tuberosity midway between the head of the 

 femur and the outer part of the trochanter, and the neck rising to support this tube- 

 rosity is somewhat convex transversely : there is no trace of this tuberosity in Bipro- 

 todon, and the fore part of the neck is concave transversely. The small trochanter, 

 which in Elephas, as in Biprotodon, is a long longitudinal ridge, is situated lower down in 

 Prohoscidia. The ridges continued from the great trochanter upon the shaft represent, 

 in that order, " linese asperse," of which there is no trace in Biprotodon. 



The difl'erences become more marked at the lower end of the bone. The rotular 

 surface or pulley is absolutely as well as relatively narrower in Elephas ; it has a more 

 anterior aspect, is supported on an anterior production or expanse of the femur ; the 

 sides of the pulley are parallel, subequally developed; there is no production of the 

 inner one as in Biprotodon. The outer as well as the inner part of the rotular articular 

 surface is distinct from that surface in the corresponding condyle. Both condyles are 

 convex and equally promment behind in Elephas ; in which genus there is no trans- 

 verse hollowing of the outer condyle, giving a trochlear character with production of 

 the outer border of that condyle as in Biprotodon. The intercondylar groove is deeper 

 and narrower in Elephas than in Biprotodon. 



Omitting the notes of comparisons of the femur of Biprotodon with that in other large 

 quadrupeds, the essential correspondence throwing true light on the determination of 

 the species to which it belongs, and the affinity of that species, is found in the Po 'ephaga 

 or Macropodidce exclusively. It is there only that one finds the transverse excavation 

 of the surface of the outer femoral condyle, producing the contrast of a trochlear cha- 

 racter of surface with the uniform convexity or ball-like prominence of the inner condyle. 

 In the Great Kangaroos {Macropus major, M. laniger) the character is exaggerated, the 

 channel is deeper, and its outer border is more produced. The rotular surface is broad, 

 with unsymmetrical sides in Macropus, the inner border being sharpest, though less 

 produced anteriorly than in Biprotodon. 



* See Osteological Catalogue of the Museum of the Royal College of Surgeons, 4to, p. 481. 



