SKELETON OF MARSUPIALIA. 



353 



Humerus of the 

 Koala. 



be observed in some Marsupials, as the Koala, that at the distal 

 articulation the external convexity for the radius has a greater 

 relative extent than usual, and the ulnar concavity 

 is less deep. 



The bones of the fore-arm are always distinct and 

 well developed, and their adaptation to pronation 

 and supination is complete. The prehensile faculty 

 and unguiculate structure of the anterior extre- 

 mities appear to have been indispensable to ani- 

 mals where various manipulations were required in 

 the economy of the marsupial pouch. When, 

 therefore, such an animal is destined like the rumi- 

 nant to range the wilderness in quest of pasturage, 

 the requisite powers of the anterior members are 

 retained and secured to it, as has been already 

 observed, by an enormous developement of the 

 hinder extremities, to which the function of loco- 

 motion is restricted. 



We find, therefore, that the bones of the fore- 

 arm of the Kangaroo differ little from those of the 

 burrowing Wombat, the climbing Koala, or the carnivorous 

 Dasyure, save in relative size. They present the greatest propor- 

 tional strength in the Wombat, and the greatest proportional 

 length and slenderness in the Petaurists or Flying Opossums, 

 in which the radius and ulna are in close contact throuo^h a grreat 

 portion of their extent, and thus lend a firmer support to the 

 outstretched dermal parachute. They are also long and slender 

 in the Koala. In general the radius and ulna run nearly parallel, 

 and the interosseous space is very trifling. It is mdest in the 

 Potoroos. The olecranon is well developed in all the Marsupials. 

 In the Virginian Opossum and Petaurists we find it more bent 

 forward upon the rest of the ulna, than in the other Marsupials. 

 In the Wombat, where the acromion is the strongest, and rises an 

 inch and a half above the articular cavity of the ulna, it is ex- 

 tended in the axis of the bone. The distal end of the radius in 

 this animal is articulated to a bone representing the os scaphoides 

 and OS lunare. 



The ulna, which in the same animal converges toward a point 

 at its distal end, has that point received in a dej)ression formed by 

 the cuneiform and pisiform bones ; these are bound together by 

 strong ligaments, and the pisiform then extends downward and 

 backward for two-thirds of an inch. The second row of the 

 carpus consists of five bones. The trapezium supports the inner 



VOL. II. A A 



