552 PEOFESSOE OWEN ON THE FOSSIL MAMMALS OE AUSTEALIA. 



The humerus in Marsupials is not described in either editions (1805, 1835) of the 

 'Le9ons d'Anatomie Comparee.' But in the ' Ossemens Fossiles' (4to, torn. iv. p. 284) 

 CuviER notes the precaution requisite in the examination of the distal articular surface 

 of the humerus in Marsupials on account of its resemblance to that in Carnivora. In 

 the posthumous 8vo edition of the ' Ossemens Fossiles,' tom. vii. p. 276, after the gene- 

 ralization as to the perforation of the inner condyle in Carnivora, is added : " ainsi que 

 chez les Didelphes et dans tons les animaux a bourse." So likewise De Blainville 

 states that the inner condyle of the humerus is perforated, " chez tons les Didelphes 

 sans exception," using the term in his peculiar taxonomic sense as equivalent to the 

 Marswpialia of other zoologists. I have, hov^ever, pointed out exceptions to this rule 

 in certain Dasyures [Basyurus Maiigei), Phalangers (Ph. Cookei), and Petaurists*. 



So much it seemed requisite to premise, because the imperforate condition of the inner 

 condyle also characterizes the bone in Biprotodon, differentiating it from the humerus 

 in Macropus and Phascolomys, without, however, affecting the marsupiality of the great 

 extinct Herbivore. To the description of this bone in Diprotodon I now proceed. 



The humerus (Plate XLVI.) is more nearly straight than in other Marsupials, and 

 is remarkable for the feeble development of the ridges for muscular attachments. At 

 a glance one sees its relations to the restricted offices of support and locomotion with 

 much less subserviency than in the smaller existing Marsupials to more varied applica- 

 tions of the fore limb. 



The head of the bone (ib. figs. 1 «& 2, a, and fig. 3) rises above the tuberosities [b, c), 

 forming a very large proportion of the upper end (fig. 3). It has the usual degree of 

 convexity, with a full oval contour, the long axis being transverse, and the smaller end 

 next the outer tuberosity ; it overhangs the back part of the shaft at its inner two-thirds 

 (fig. 1), but in a less degree than in the Kangaroo. The inner tuberosity [h) is represented 

 by a low broad, rough ridge, extending from the inner side along the fore part of the 

 periphery of the head to near the small outer end of the articular ball ; here it is inter- 

 rupted by a wide but very shallow representative of the " bicipital groove." The outer 

 tuberosity {c) projects in a greater degree from the outer side of the base of the head. 



The broad, low, rounded angle between the fore and outer sides of the humeral shaft, 

 continued from the fore end of the outer tuberosity (fig. 2, c), representing at first the 

 outer side of the bicipital groove, descends and assumes rather more of the character of 

 a muscular ridge at the mid length of the shaft (fig. 2, d) before subsiding. 



The liomologue (ib. c) of the short external ridge in Macropus here projects as strongly 

 from that side of the bone, but on the same transverse parallel with the lower, best deve- 

 loped part of the deltoid ridge [d). Consequently the external ridge is relatively lower 

 placed than in the Kangaroos ; it is also relatively shorter, lengthwise, and stands out 

 more abruptly at its upper part. 



The representative of the deltoid ridge divides the fore part of the shaft unequally, and 

 the broader division or tract (fig. 2, f) is internal, the narrower division or tract {ib. g) 



* Osteology of Marsiipialia, Joe. cU. p. 400. 



