PEOPESSOE OWEN ON MACEOPUS. 439 



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. This production is 

 exaggerated in the distal articular epiphysis of the Mammal, as the antero-ascending 

 process of the epiphysis, homologized by some with the astragalus, is exaggerated in the 

 Bird. 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. LXXXII. 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,/') between the femoral 

 and fibular articular surfaces of the tibial condyle {a). The fibula rapidly contracts 

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

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

 subsides into the rounded angle between the adjoining tibial facets, and is closely 

 applied thereto to near the distal end of the tibia. In this course the fibula is reduced 

 to a mere channelled plate, as shown in the transverse section (u a). It needs only 

 here to terminate in a point to complete the correspondence with the fibula of the 

 Moa or Emu ; but in the Marsupial the distal end of the fibula again slightly expands, 

 and contributes by its epiphysis an outer malleolar buttress (ib. figs. 9, 11, b) to the 

 mammalian ossifications in the tarsal segment of the foot. Had the fibula of the Bird 

 been so continued, it would have had its terminal epiphysis ; and this, like the tibial 

 one, would have supplied Gegenbaur and his followers with a tarsal ossicle. 



The ossified tarsal segment is singularly modified in Macropodidse (PL LXXXIII.), 

 in relation to the concentration of the powers of the hind feet, as saltatory locomotive 

 instruments, upon the outermost pair of toes, and mainly upon one of these, answering 

 to the fourth in the pentadactyle foot. 



The narrowness of the hind foot as compared with the fore foot, which leads to the 

 displacement of the tarsal homotype of the carpal scaphoid to a more distal position in 

 its segment, is extreme in the Kangaroos — and being associated with atrophy of the 

 inner or tibial side of the metatarsus, renders still more obscure the true character of 

 the "naviculare" (PI. LXXXIII. fig. 1, n): it will therefore be described in the order 

 followed in anthropotomy. 



The homotype of the carpal " lunare " almost monopolizes the distal articulation of 

 the leg-bones. In the tarsus it is the astragalus (ib. figs. 3, 4, 5), and, in the Kangaroos, 

 is subdepressed, triangular, with the base turned forward (figs. 3 & 4) : viewed from the 

 inner or tibial side (ib. fig. 5) it is arched, with the convexity towards the leg. 



The upper surface (fig. 3) is chiefly formed by the trochlear articulation ( i ) for the 

 tibia, convex from behind forward, concave transversely, passing into a convex outer 



