PROFESSOR OWEN ON MACROPUS. 429 
The first lumbar vertebra (Pl. LX-XV. fig. 11) is marked by the reduction of the diapo- 
physis(d) to asmall rudiment. The metapophyses (7) have usurped the place of the pre- 
zygapophyses in all the lumbars. ‘The anapophyses (a) become shorter, broader, and 
compressed ; they diminish in the fourth and fifth (fig. 13, a), and disappear in the sixth 
lumbar. The diapophysis increases to the fifth, with a forward production in the second 
and third (fig. 12, d), together with a hinder production in the fourth and fifth (fig. 13, 
d, d'), the whole plate being depressed ; in the last lumbar it is shortened, but thickened. 
The centrums increase from a length of 1 inch 3 lines in the first lumbar (ib. fig. 11) to 
that of 1 inch 9 lines in the fifth lumbar (fig. 15). The sixth again becomes shorter, but 
broader. The neural spine (ns) becomes narrower antero-posteriorly and longer in the 
third lumbar; then again shortens in the fifth and sixth. The vertical “ epineural,” 
perforations are present on both sides of the neural arch in all the lumbars. The intra- 
neural canals communicate with the epineural ones, and in the last lumbar are their 
direct continuations downward and forward. One or two outlets of veins excavate the 
lower surface of the centrum in each lumbar vertebra. 
The sacrum (Pl. LXXVI. figs. 8 & 9) consists of two coalesced vertebre. ‘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, 
in, in). The metapophyses (ib. ib. m, m) have oblique shallow facets (ib. fig. 9, 2, z 
at the lower part of their inner surfaces for junction with the postzygapophyses of the 
last lumbar vertebra. The pleurapophysial part (fig. 8, pl) of the transverse process 
expands as it recedes from the centrum and neural arch to form the large reniform 
articular surface (fig. 9, p/') for the iliac bone, to which the second sacral contributes 
only the hinder angle (ib. pl). This articular surface equals half the length of the entire 
sacrum. Above or behind the flat syndesmotic surface (pi’) is a smooth depression. 
The heemal surface of both centrums is concave lengthwise, convex transversely. A 
wide circular intervertebral canal (fig. 9, 7) 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, ms) 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. pl) 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. 
