PROFESSOR OWEN ON THE SPECIES OP PHASCOLOMYS. 489 



a difference of proportion corresponding with the indication afforded by the glenoid 

 cavity of the scapula ; its antero-posterior or short diameter is greater, in comparison 

 with its transverse or long diameter, in Phascolomys latifrons (ib. fig. 2, a), where it 

 extends lower down and is narrower at its termination at the back of the humerus, than 

 in Phase, platyrhinus (ib. fig. 4, a). The entire bone is stronger, broader in proportion 

 to its length, in Phase, latifrons (ib. figs. 1 & 2). 



In both species the proximal tuberosities are well developed, but they are relatively 

 more so in Phase, latifrons (figs. 1 & 2, S, c). In this species the ' ecto-tuberosity ' 

 extends its base over half the diameter of the fore part of the humerus (ib. fig. l,l)\ 

 in Phase, platyrhinus over two fifths (ib. fig. 3, h). 



The ento-tuberosity protrudes inward further in Phase, latifrons (ib. figs. 1 & 2, c) 

 than in Phase, platyrhinus (ib. figs. 3 & 4, c). 



The ridge {d) for the insertion of the conjoined ' teres major ' and part of the ' triceps' 

 is shorter, thicker, more prominent, and better defined in Phase, latifrons ; it is situated 

 chiefly on the thenal or fore part of the shaft, near the inner surface ; but more of it is 

 visible in the anconal view in Phase, latifrons (fig. 2, d) than in Phase, platyrhinus 

 (fig. 4, d). 



The line of insertion [e, e') of the large and complex 'pectoralis' extends from the 

 lower and fore part of the ecto-tuberosity to that of the deltoid ridge (f), nearly along 

 the mid line of the fore part of the humerus ; but it is to the inner side of that line in 

 Phase, latifrons (fig. 1, e, c'), and to the outer side in Phase, platyrhinus (fig. 3, e, d). 



The outer contour of the humerus curves almost parallel with the ' pectoral ' ridge to 

 the projecting angle of the deltoid one (/) in Phase, latifrons (fig. 1). This angle is 

 less prominent in Phase, platyrhinus (fig. 3, f), and the distance between it and the 

 ' predeltoid ridge ' {g) is less. 



The ' supinator ridge ' (A, li!) is strongly developed in both species, and terminates 

 above in a freely projecting, sometimes unciform process (/*) ; below, it rapidly expands 

 into the ectocondylar triangular surface (A'), giving attachment to the origin of the 

 ' extensor digitorum ' muscle. The entocondylar process {i) is more produced and angular, 

 and is largest in Phase, latifrons (ib. fig. 1). The bony bridge {k) extending from the 

 fore part of the humeral shaft to that angle (i) is thicker in Phase, latifrons (fig. 1) than 

 in Phase, platyrhinus (fig. 3). The foramen which it defines is large and elliptic in both 

 species. 



The radial division of the distal articular surface {I) is hemispheroid anteriorly (ib. 

 fig. 1, I), the convexity subsiding somewhat as it is produced backward ; the ulnar divi- 

 sion (m) is almost flat transversely, convex from before backward ; the joint in this 

 direction is narrowest at its middle, where the ulnar passes into the radial division 

 (PL LXXIV. fig. 13). Both dirisions are larger, especially the ulnar one, in Phase, 

 latifrons (fig. 1, m) than in Phase, platyrhinus (fig. 3, m). The shaft of the humerus is 

 least thick between the deltoid and supinator crests ; and a deep sulcus is continued from 



