301 



Marsupialia it assumes the character of a distinct process from the same part, and 

 attains its greatest development in the Wombat and Koala, in the latter of which it is 

 forcibly curved downward and inward. 



The humerus in the Dasyures resembles that of the Dog tribe in the imperforate 

 condition of the entepicondyle, but differs in the more marked development of the 

 muscular ridges, especially of that which extends upward from the ectepicondyle for 

 the origin of the great supinator muscle; this ridge is terminated abruptly by the 

 smooth tract for the passage of the musculo-spiral nerve. In all the other genera of 

 Marsupials, including Thylacinus and Phascogale, the humerus is perforated above the 

 internal condyle. It is so in Petaurus macrurus and Pet. taguanoides ; but in the 

 Petaurus sciureus the foramen is represented by a deep notch ; in Phalangista cookii 

 both foramen and notch are wanting. The supinator ridge is much developed in the 

 Petaurus macrurus and Pet. sciureus, and is notched at its upper part ; but this notch 

 does not exist in Pet. taguanoides. In the Kangaroos, Potoroos, Wombat, and Koala 

 the ridge extends in the form of a hooked process above the groove of the radial 

 nerve. In all these, and especially in the W ombat, the deltoid process of the humerus 

 is strongly developed : it is continued from the external tuberosity down the upper half 

 of the humerus — except in the Petaurists, where, from the greater relative length of 

 the humerus, it is limited to the upper third. The interspace above the condyles is 

 occasionally perforated in Macrotis and the Tasmanian Wombat. Both condyles are 

 convex anteriorly, the ulnar one is transversely concave behind. 



The bones of the forearm are always distinct and well developed ; and their adapta- 

 tion to pronation and supination is complete. The prehensile faculty and unguiculate 

 structure of the anterior extremities appear to have been indispensable to animals 

 where various manipulations were required in the economy of the marsupial pouch. 

 When, therefore, such an animal is destined, like the Ruminant, to range the wilderness 

 in quest of pasturage, the requisite powers of the anterior members are retained and 

 secured to it by an enormous development of the hinder extremities, to which the 

 function of locomotion may be and often is restricted. 



We find, therefore, that the bones of the forearm 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 proportional strength in the Wombat, and 

 the greatest proportional length and slenderness in the Petaurists, in which the radius 

 and ulna are in close contact through a great 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 widest in the Potoroos. The olecranon is well developed in 

 all existing Marsupials ; it is anomalously absent in Diprotodon and Nototherium. In 

 the Pet. taguanoides it is expanded, and truncate at the upper extremity ; 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 olecranon is the 



27* 



