200 
PROCESSOR OWEN ON THE EOSSIL MAMMALS OF AUSTRALIA. 
The sacrum (Plate 21. fig. 1) consists of two vertebrse with the characters of those 
of Macropus rufus *, but with a difference of size shown in the following admea- 
surements : — 
Macrojous 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 (c 2 ) and 
first caudal ( cd 1 ) as to have kept those vertebrse 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) are 
rather smaller, relatively, than in 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. Jc, Jc) 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 
rufus are closely repeated, with the difference of size and slight increase of breadth over 
length, as in the sacrum ; and these permit an inference that the tail in Palorchestes 
corresponded in strength, if not quite in relative length, to that in Macropus. 
§ 4. Palorchestes (Os innominatum). — The pelvis of the Kangaroo is characterized 
by a long prismatic ilium, an oblong tuberosity above or anterior to the acetabulum, a 
“ pectineal ” or “ ileo-pubic ” process, the articular surfaces for the marsupial bones, 
the broad, compressed, subprismatic form of the ischium, the slenderness of the pubis, 
and the great length of both those elements of the pelvic arch. 
The length of the pelvis due to the great extension of the os innominatum both in 
front and behind the acetabulum is a well-marked feature of resemblance to the same 
* “ Osteology of Marsupialia. — Part V.,” Trans. Zool. Soc. vol. is. p. 429, pi. Ixxvi. 
f Phil. Trans. 1874, p. 253. 
