38 G 



bone is occupied by the two tuberosities and their intervening (bicipital) groove,^). The 

 ectotuberosity (ib. c) is a long thick ridge ; the entotuberosity (ib. b) is shorter and 

 thicker ; both rise above the level of the head (ib. fig. 2). The proximal third of the 

 shaft is four-sided ; the two broader sides (ib. fig. 2, 1, r) are on the anconal aspect, and 

 meet at the round or obtuse ridge (ib. h) continued from below the overhanging head 

 one third down the bone. The facet on the ulnar side (I) of the ridge is bounded at its 

 lower half by the ridge (e) for the insertion of the " pectoralis." The two facets on the 

 thenal side of the proximal part of the shaft are of unequal breadth ; the broader one 

 (ib. fig. 1, g) is fiat, and is bounded below by the ridge e and the stronger deltoid ridge 

 (ib. d), which is continued below the middle of the shaft. The fourth facet (ib./) is 

 the narrowest ; it is bounded on the outer (radial) side by the deltoid ridge, which is 

 continued from the ectotuberosity downwards ; a thicker ridge from the entotuberosity 

 (ib. t) subsides upon a roughish surface (ib. fig. 3, v) about one third down the bone. 

 The shaft contracts below the deltoid region, assumes the cylindrical form for a short 

 extent, and sends off the supinator ridge (ib. figs. 1 & 2, Jc'). 



A strong bony column (ib. figs. 1 & 3, s) rises more gradually, at a lower part of the 

 shaft, from the fore and inner part of the distal expansion, then springs from the 

 surface and extends freely downward and inward for about half an inch, and again 

 unites with the bone, subsiding above the entepicondyle (ib. fig. 1, i). The column (s) 

 bridges over a canal, 5 lines in long diameter, for the passage of the median nerve and 

 an artery. The supinator ridge (ib. k, H) commences abruptly at the outer side of the 

 distal third of the shaft : its rough thin border is slightly bent forward, and thickens a 

 little before it is lost in the ectepicondyle (k). The distal end (ib. fig. 5) is subcompressed 

 antero-posteriorly ; the transversely extended articular surface is divided into two parts 

 by a broad groove, shallow anteriorly, deeper behind, and is slightly produced forward 

 or " thenad," and more so at its outer or radial end. This articular surface presents 

 a convexity broadest in front (fig. 1, n), contracting to a point or ridge behind (fig. 2, n) ; it 

 is the " radial " condyle, and articulates with the shallow circular cavity (PI. LXX. 

 fig. 7) at the proximal end of the radius. The inner or ulnar surface is slightly convex 

 transversely at its fore part (PI. LXIX. fig. 1, o), but is mostly concave transversely, 

 and convex from before backward, forming a trochlear surface with two parallel 

 borders, the inner of which is the most prominent (ib. fig. 2, o). The fore part of the 

 articular surface (fig. 1, n, o) is undulated transversely, a feeble convexity intervening 

 between those of the ulnar (o) and radial (n) divisions. There is no coronoid depres- 

 sion, and only a shallow olecranal one (ib. fig. 2, m). 



In the Kangaroo, as in all Mammals charged with the manipulation of a nursing- 

 pouch, the elbow-joint is fashioned to facilitate the movements of pronation and supi- 

 nation of the fore paw 1 , as well as those of flexion and extension of the forearm. The 



1 These movements are least free in Chceropus, in which the functional digits of the fore paw are reduced 

 to two (n. & ni.). 



