PROrESSOE OWEN ON THE FOSSIL MA]MMALS OF AUSTRALIA. 



549 



the articular end of the bone (ib. a, c) the base of the triangle, which is elongate and 

 irregular. 



The articular or glenoid cavity (ib. d) presents the usual oval shape with the small 

 end upward (ib. fig. 3) ; the concavity is deepest lengthwise, and the apical part is most 

 produced. The outer border beneath the acromion (e) has been broken off, indicative 

 of its prominence, which is better preserved in the articular cavity of the fragment of 

 the right scapula, showing its resemblance to that part in Macropus. This border 

 subsides, becoming thick and convex as it approaches the small or coracoid end of the 

 cavity. The lower border is continued into Yig. 6. 



a rugged triangular surface beneath (fig. 3, a) 

 for the attachment of the long head of the 

 triceps ; the upper apical part is produced, 

 beak-like, beyond the base of the coracoid 

 [c). The inner margin is low near the apex, 

 but less obtuse than the corresponding part 

 of the outer one ; it is more produced as it 

 descends ; but this margin subsides gradually 

 into the subscapular one. 



The spine (ib. fig. 1,/") begins by a gradual 

 elevation of the lower or hinder half of the 

 hinder surface of the "base" (J), which ele- 

 vation contracts as it rises from that surface 

 to a thickness of 1^ inch. The free border, 

 of this thickness, is also flat ; the spine gra- 

 dually rising as it advances, describes a 

 slight curve toward the upper or anterior 

 costa {g) ; the lower margin of the free border 

 becomes most produced, and, as the spine 

 expands into the acromion (e), this margin 

 also expands and becomes rough for muscular 

 attachments, and in the present specimen 

 forms the most prominent part of the acro- 

 mion ; but the end of this process is broken 

 off. From a pencil-sketch of this scapula 

 made by Sir Thomas Mitchell when it 

 arrived at Sydney (Woodcut, fig. 6), the acro- 

 mion [e) continued to expand to an obliquely 

 truncate end, having the upper or fore angle most produced, and, as it were, slightly 

 twisted towards the coracoid (c) (indicated by the dotted line in fig. 1, Plate XLV.). As 

 the spine (ib. /') rises from the scapular plate, it becomes compressed or thinner beneath 

 the free margin, and presents a smooth concave surface to each scapular fossa (^,y). 



Scapiila of Bijorotodon : one-fifth nat. size. 



