438 PEOFESSOE OWEN ON MACEOPUS. 



convex and undulated by a transverse rising and shallow groove (ib. d) : there is a 

 slight depression in front of each articular sui-face. 



The procnemial ridge (ib. fig. 1, h) extends from the tuberosity (ff) downward, 

 retaining a sharpish margin, slightly bent outward, for an extent of 3 inches, then 

 becomes thicker, smoothly rounded, and subsides ; it seems to be resumed as a low 

 angle between the outer and inner surfaces of the lower half of the shaft (ib. fig. 5, h). 



The ectocnemial ridge (ib. figs. 2 and 3, i) is sharper and less produced superiorly 

 than the preceding (/*) ; but it becomes rather more prominent as it descends, and 

 begins to thicken and subside near the lower half of the shaft. At 5 inches distance 

 from it its origin it is grooved behind by the tibial medullary artery, which enters the 

 bone an inch lower down : the canal runs distad. 



The proximal third of the inner surface (ib. fig. 2, r) is smooth and flat, below which 

 it gradually becomes convex, and is again rather flattened at the distal third of the shaft. 



The hind facet (ib. fig. 3, I) is the narrowest : it is slightly concave across at its 

 outer half, and convex at its inner half: the concavity deepens as the surface is 

 extended by the outgrowth of the ectocnemial ridge, where the medullary artery enters 

 the bone. The hind part of the outer condyle or articular surface (a) is produced to 

 give depth to the transverse fibular groove (ib. figs. 1 & 3, e), which becomes continuous 

 by the hind facet (fig. 3,/') with the surface for the external femoral condyle. 



The distal end of the tibia (ib. fig. 7) is more expanded transversely than from 

 before backward. The inner malleolus (m) has greater fore-and-aft breadth than 

 vertical extent: its outer surface is bituberculate ; the opposite or articular surface 

 (ib. fig. 6, n) is convex transversely, but extended vertically to join the horizontal 

 terminal articular surface ; this is feebly trochlear and bounded externally by the outer 

 malleolus, due to the distal epiphysis of the fibula. 



The likeness of the Kangaroo's tibia to that of a large Struthious bird is striking 

 and instructive, and is much closer than that ofiered by the tibia of Megalosaurus or 

 any other Dinosaur. 



The narrow posterior surface (ib. fig. 8, /) is bounded above by the convex promi- 

 nences of the two proximal articular surfaces and their intervening notch ; and, as in 

 the Bird, the posterior is the narrowest of the three surfaces. The summit of the 

 procnemial ridge is formed by an epicnemial tuberosity, which long retains, in both the 

 Bird and the Marsupial, its epiphysial distinctness. 



The "outer facet" of the shaft (ib. fig. 1, Jc) which the procnemial ridge bounds 

 and mainly forms, at the proximal part of the bone, is deeply concave across. The 

 inner surface, owing, in both, its proximal breadth mainly to the procnemial produc- 

 tion, is smooth and flat or but feebly convex across. 



The distal articular surface is supported on an epiphysis ; and this sends upward at its 

 fore part a process (ib. fig. 5, p) wedged, as in the Bird, into a groove of the corresponding 

 part of the diaphysis : the epiphysis is later in its confluence than in the Bu-d. The 



