140 



and Phalangers the acromion is, as it were, bent downwards, so as to 

 present a flattened surface to the observer. In the Potoroos and 

 Opossums this appearance is produced by a true expansion of the 

 acromion. In the Perameles the caracoid process is merely repre- 

 sented by a slight production of the superior part of the glenoid ca- 

 vity. In the Kangaroo and Potoroos it forms a protuberance on 

 the upper part of the head of the scai)ula. In the other Marsupiatu 

 it assumes the character of a distinct process from the same ])art ; 

 and attains its greatest develojiment in the Wombat and Koala, in 

 the latter of which it is forcibly curved downwards and inwards. 



" The humerus m the Dasyures and Thjdacine resembles that of the 

 dog-tribe, in the imperforate condition of the inner condyle, but dif- 

 fers in the more marked development of the muscular ridges, espe- 

 cially that which extends upwards from the outer condyle, for the 

 origin of the great supinator. This ridge is terminated abruptly by 

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

 Phal. Cookii the internal condyle is imperforate, and in Petavrvs 

 Sciureus iti^ deeply notched ; but in other Phalangers and Petaurists, 

 as also in all the other genera of Marsupials, the internal condyle 

 of the humerus is perforated. 



" The ridge above the external condj'le is much developed in the 

 Petaurus macrurus and P. sciureus, and notched at its upper part ; 

 there is the same structure in Phal. Vulpina, but it docs not exist 

 in Phal. Cookii. I find similar difi^erences in the develoi^ment of 

 the supinator or outer ridge in the genus Perameles ; in the Per. 

 lagotis it is bounded above by a groove ; in Per. grtsca it is less 

 developed and less defined. In the Kangaroos, Potoroos, Wombat 

 and Koala, the outer condyloid ridge extends in the form of a 

 hooked process above the groove of the radial nerve. In all these, 

 and especially in the Wombat, 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 of the condyles is occasionally 

 perforated, as in the Perameles lagotis and Wombat. The articular 

 surfaces at both extremities of the humerus have the usual form ; 

 but it may be observed, that in some Marsupials, as the Koala, the 

 external convexity at the distal articulation for the radius has a 

 greater relative extent than usual, and the ulnar concavity is less deep. 



" The bones of the fore-arm present little to detain our notice. 

 They are always distinct and well-developed, and their adaptation 

 to pronation and supination is comi^lete. The prehensile faculty 

 and unguiculate structure of the anterior extremities appear to have 

 been indispensable to animals requiring to perform various manipu- 

 lations in relation to the oeconomy of the Marsupial pouch, and when 

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

 in quest of pasturage, the requisite powers of the antei-ior members are 

 retained and secured to it by an enormous development of the hinder 

 extremities, to which the function of locomotion is almost restricted. 

 " We find, therefore, that the bones of the fore arm of the Kangaroo 

 dlfFcr little from those of the burrowing Wombat, the climbing 



