554 PKOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



olecranon not quite entire ; it is a strong but low trihedral process, smooth and concave 

 on the inner side, roughish and flattened behind ; with a smooth almost horizontal tri- 

 angular surface at the upper part. The breadth of the base of the olecranon is 3 inches 

 10 lines; the circumference of the base is 13 inches. The articular surface answering 

 to the " greater sigmoid cavity " is concave, longer and deeper from before backward 

 than from side to side. From its upper and outer part a less concave articular surface 

 is continued upon the inner side of the base of the olecranon. The lower part of this 

 surface, which may have afforded the " lesser sigmoid cavity " to the radius, is broken 

 away. The rough tract for syndesmotic junction with the radius extends down the outer 

 side of the shaft inclining obliquely forward : it is about an inch in breadth. There is 

 a small but well-marked tuberosity and depression, on the outer or radial side of the 

 ulna, 1 J inch below the " greater sigmoid cavity," answering to a corresponding process 

 in the Wombat. The elongation of the olecranon in that burrowing Marsupial, aug- 

 menting the lever for working the fore paw, does not exist, and was not needed in the 

 gigantic gradatorial Biprotodon. The portion of ulna above described indicates a massive 

 and powerful fore arm, and has encouraged me to indicate the continuation of the ulna, 

 as a distinct bone, to the carpus, in my restoration of Biprotodon (Plate L.). The canal 

 for the medullary artery enters the bone on the inner side (that next the radius) below 

 the '-sigmoid" articular cavity, and the canal is directed inward and a little upward. 

 This fossil was obtained in the bed of the Condamine River, west of Moreton Bay, 

 by Sir Thomas Mitchell, C.B. 



§ 8. Pelvis. — In a collection of bones from fluviatile freshwater deposits at Eton Vale, 

 Darling Downs*, in the usual massive or weighty, semipetrified condition of fossils from 

 those beds, were fragments of a large pelvis, readjustible to the extent of giving a great 

 part of the sacrum and ilia, both acetabula, the acetabular portion of each ischium to 

 the extent of 7 or 8 inches, and about 5 inches of the acetabular end of each pubis. 



The sacrum consists of two vertebrae (Plate XLVII. s i, s 2), uniting with the ilia 

 (ib. 62) by a terminal expanse of the transverse processes (ib. fig. i,pl 2), coequal with 

 the antero-posterior extent of the entire sacrum, and giving to that bone a subquadrate 

 form one-third broader than it is long. Much of the anterior articular surface of the 

 body of the first sacral (fig. 1, 5 1) is preserved, and a smaller proportion of the posterior 

 surface of that of the second sacral (ib. s 2). Both surfaces show the usual mammalian 

 flatness and concentric lineation for union by intervertebral sclerous substance with 

 contiguous centrums : the rougher surface shows the loss of the epiphysial plate. The 

 transverse diameter of the fore part of the first centrum is 5 inches ; the vertical (neuro- 

 ha3mal) diameter is 3 inches. The transverse diameter of the hind end of this centrum, 

 giving that of the fore end of the succeeding anchylosed centrum (s 2), is 3 inches 5 lines. 

 The ha^malf surface of both centrums (Plate XLVII. fig. 1, s 1, 2) is flat, subquadrate, the 



* These fossils, collected in the above-named locality by Edwaed S. Hill, Esq., were liberally presented to 

 the British Museum by Sir Danikl Cooper, Bart., in 1864. 



t In noting the position and aspect of the parts of this pelvis according to anthropotomical description, 



