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the tibia gradually contracts to a tuberosity (g), the non-articular surface behind which 

 is less rough, is moderately convex and undulated by a transverse rising and shallow 

 groove (ib. d) : there is a slight depression in front of each articular surface. 



The procnemial ridge (ib. fig. 1, h) extends from the tuberosity (g) 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 (h) ; 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) 

 of the shaft is smooth and flat, below which it gradually becomes convex, and is again 

 rather flattened at the distal third. 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 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,f) with that surface. 



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 distal articular surface of the tibia, also, 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 Bird. The inner articular part of the distal trochlea in the Bird, shows its 

 homology with that of the inner malleolus in the Marsupial by its greater production. 

 The length of the tibia in the male Wallaroo affording the bone here described is 

 1 foot 8 inches ; that of the fibula is half an inch shorter. 



The fibula (PI. LXXIV. figs. 8-11) has its proximal end expanded antero-posteriorly, 

 with a corresponding elongate angular articular tract (ib. fig. 10, a) fitting the angular 

 groove (ib. fig. 1, e) of the outer tibial condyle; a tuberous production (ib. figs. 8, 10, 

 b) of the hinder part, which does not rise above the level of the tibial condyle, and to 

 which is ligamentously attached the " fabella " in the tendon of the " gastrocnemius 

 externus," plays upon the hinder facet of continuity (ib. fig. 3, f) between the femoral 

 and fibular articular surfaces of the tibial condyle («). The fibula rapidly contracts 

 below its proximal and articular epiphysial end, joins the ectocnemial ridge (ib. figs. 2 

 & 3, i) about one fourth of the way down the shaft, becomes concave as that ridge 



39* 



