3.')2 ANATOMY OF VERTEBRATES, 



a remarkably deep notch ; they become compressed as they ap- 

 proach the acromion, to which they are attached by an extended 

 narrow articular surface. 



In the Koala the clavicles are also very strong, but more com- 

 pressed than in the Wombat, bent outward in their Avhole extent, 

 and the convex margin formed, not by a continuous curve, but 

 by three almost straight lines, with intervening angles ; progres- 

 sively diminishing in extent to the outermost line which forms 

 the articular surface mth the acromion. In the Myrmecobius 

 the clavicles are subcompressed and more curved at the acromial 

 than at the sternal end. In most of the other Marsupials the 

 clavicle is a simple compressed elongated bone, with one general 

 outward curvature. 



The humerus in most Dasyures resembles that of the Dog-tribe 

 in the imperforate condition of the inner condyle, but differs in 

 the more marked developement of the muscular ridges, especially 

 of that which extends upward from the outer condyle 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 that I have examined the 

 internal condyle of the humerus is perforated. But in some 

 species of Petaurus, as Petaurus sciureus, the foramen is repre- 

 sented by a deep notch ; and in the Phalangista CooMi, both 

 foramen and notch are wanting, i The ridge above the external 

 condyle is much developed in the Petaurus macruriis and sciureus, 

 and notched at its upper part, but this notch does not exist in 

 Pet. taguanoides. I find similar differences in the developement 

 of the supinator, or outer ridge, in the genus Perameles ; in the 

 Per. lag Otis it is bounded above by a groove ; in Per. Gunnii it is 

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

 Wombat, and Koala (fig. 225), the outer condyloid ridge ex- 

 tends 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, fig. 212, 53, 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 



^ In the other species of Phala7igista, and in the Petaurus taguanoides and macrurns, 

 the internal condyle of the humerus is perforated. In a Thyjacine I found it per- 

 forated ; and in one Ursine Dasyure in the left humerus, but not in the right. 



