480 



Family MACHOPODIDiE. 



Extinct Genera and SrEciEs. 



Bones of the Trunk and Extremities. 



§ 1. Pal 'or rhest est (Sacrum). — In the series of fossil bones which have been trans- 

 mitted to me from the drift-deposits of Darling Downs have been vertebra; and portions 

 of the vertebral column, from which I select for the subject of the present Section the 

 sacrum of a Macropod of a size and proportion corresponding with those of the skull of 



Palorchestes Azael. 



The sacrum (Plate CXXIX. fig. 1) consists of two vertebrae with the characters of 

 those of Macropus rufus (Plate LXVIII. figs. 8, 9, Plate LXXI. fig. 1), but with a 

 difference of size shown in the following admeasurements :— 



Macrojms rufus. Palorchestes. 



in. lines. in. lines. 



Length of sacrum (at zygapophyses) 3 2 4 10 



Breadth of sacrum (across fore part) 3 5 5 6 



Breadth of centrum of first vertebra 17 2 6 



The Kangaroo yielding the recent bone compared was the largest example seen by 

 Mr. Gould in his travels in Australia, and no specimen of Macropus major has yet 

 been recorded of superior size. 



The comparatively gigantic leaper yielding the fossil seems to have been an aged 

 individual, for so much anchylosis has taken place between the second sacral (Plate 

 CXXIX. fig. 1, c 2) and first caudal (ib. cd i) as to have kept those vertebrae in natural 

 connexion during the period of petrifaction. 



The transverse processes of the second sacral take a greater relative share in the 

 formation of the sacro-iliac symphysis in Palorchestes than in the above-named recent 

 species, and the shape is rather more subquadrate than triangular. The joint between 

 the first and second sacral is not obliterated. The intervertebral foramina (ib. i, i) are 

 rather smaller, relatively, than Macropus rufus, and suggest that the hind limb may 

 not have predominated over the fore limb in so great a degree in the larger and 

 heavier Kangaroo. The pair of ridges on the haemal surface of the centrum of the 

 second sacral (ib. k, k) are better marked in the fossil. In this the neural arch of the 

 first sacral has been broken away. 



The first caudal vertebra of Palorchestes (ib. figs. 2, 3) is 2 inches 11 lines in length, 



1 inch 6 lines across the hinder articular end of the centrum. The base of the lamelli- 

 form depressed transverse process (ib. d, d) is 1 inch 8 lines in extent, reaching within 



2 lines of each articular end of the centrum. The longitudinal extent of the base of 

 the neural spine is 1 inch. The characters of the corresponding vertebra in Macropus 



