PEOPESSOE OWEN ON MACEOPUS. 429 



The first lumbar vertebra (PI. LXXV. fig. 11) is marked by the reduction of the diapo- 

 physis (d) to a small rudiment. The metapophyses (m) have usurped the place of the prae- 

 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. 13). 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 (PI. LXXVI. 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, 

 in, in). 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, j)^) 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.^j^"). 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. s') of the first sacral. The postzygapophyses 

 (s" 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. pt") 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. 



