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The sacrum (PI. LXVIII. figs. 8 & 9) consists of two coalesced vertebrae. The first, 

 with a broad subconvex articular surface (ib. fig. 8, c) for the last lumbar vertebra, 

 contracts to two thirds that breadth where it joins the second sacral ; the body of this 

 again slightly expands to form the surface for the first caudal. The pair of venous 

 canals opening on the upper surface of the centrum, within the neural canal, unite into 

 one, which perforates the under surface. The pair of vertical epineural canals (ib. 

 fig. 9, en, en) open near the fore part of the neural arch as " intraneural canals " (ib. fig. 8, 

 m, Ml). The metapophyses (ib. ib. m, m) have oblique shallow facets (ib. fig. 9, z, z) 

 at the lower part of their inner surfaces for junction with the postzygapophyses of the 

 last lumbar vertebra. The pleurapophysial part (fig. 8, pi) of the transverse process 

 expands as it recedes from the centrum and neural arch to form the large reniform 

 articular surface (fig. 9,^/') for the iliac bone, to which the second sacral contributes 

 only the hinder angle (ib. Jt>^")- This articular surface equals half the length of the entire 

 sacrum. Above or behind the flat syndesmotic surface (pi') is a smooth depression. 

 The haemal surface of both centrums is concave lengthwise, convex transversely. A 

 wide circular intervertebral canal (fig. 9,^') perforates the sacrum vertically on each side 

 of the confluence of the centrums ; the dorsal or neural opening is partially overhung 

 by a rudiment of the postzygapophysis (ib. z') of the first sacral. The postzygapophyses 

 (z" z") of the second sacral are normally developed, and diverge from the upper and 

 hinder part of the neural arch ; their articular surface is flat and looks downward and 

 outward. The neural spines of the two sacrals are confluent as a thin compressed crest 

 of bone (ib. fig. 9, n s) one inch and a half in extent, and half an inch in height. The 

 transverse process of the second sacral is continued from the hind angle of the articular 

 pleurapophysis (ib. ib. pi") as a thin depressed plate to the hind end of the base of the 

 neurapophysis, beyond which the centrum (fig. 9, c) extends about three lines. 



The chief vertebral characteristic of the Macropodidee is the strength and length of the 

 caudal region, and the number of vertebrae composing it. In Macropus rufus there are 

 twenty-two caudals, fourteen of which, after the second, have the haemal arch. The 

 metapophyses (PI. LXVIII. fig. 10, m, m) resume a considerable size in the first caudal, 

 in the form of quadrate plates an inch in length by eight lines across the truncate ends ; 

 the lower half of the fore border is slightly produced as a zygapophysis (z), the surface 

 of which is continued back upon the base of the metapophysis. The neural spine is 

 represented as a pair of low ridges (ns) diverging to the postzygapophyses (z 1 , z'). These, 

 in the first caudal, resemble those of the second sacral. The diapophyses are depressed 

 plates, extending horizontally outward and backward, where they end in obtuse rather 

 thickened points (ib. fig. 10, d, d). The second caudal chiefly differs from the first in 

 the smaller postzygapophyses. The haemal arch (fig. 11) is small, with a longish slender 

 spine (h s). The third and following caudals have no zygapophysial junctions, but 

 coarticulate by their centrums only. The diapophyses are much diminished in the 

 fourth caudal, and are reduced to tuberosities terminating the sharp lateral longitudinal 



