PKOFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 
555 
contour being straight lengthwise, the coalesced ends making no projection forward or 
haemad. 
The upper and anterior border of the first centrum, however, is abraded, as is the lower 
and anterior border of the second centrum ; both being entire, would give a slight con- 
cavity to the longitudinal contour of the haemal surface. The length of the sacrum is 
5 inches 8 lines, that of the anterior centrum being 3 inches 3 lines. The rib-part 
(pi i) of the broad and thick transverse process of the first sacral recedes slightly as it 
expands, passing outward to join the ilium (62), with a slight curvature convex hsemad. 
The greater part of the haemal surface of the process is flat transversely, becoming 
slightly concave at its hind part ; lengthwise it is here convex from before backward. 
The line of the confluence with the ilium, indicated by a slight eminence (ib. fig. 1, 
p, p ), is feebly curved with the convexity outward. The sacro-iliac symphysis is 8 inches 
in length following the curve ; the origin of the sacral rib or transverse process has a 
fore-and-aft extent of 3 inches 9 lines. The direction of the origin of the process in both 
vertebrae is oblique, from near the neural surface of the centrum anteriorly to the haemal 
one posteriorly. The hind border of the origin of the first transverse process forms the 
fore margin of the wide anterior outlet of the intervertebral canal (i), which expands into 
an infundibuliform channel backed by the succeeding transverse process (pi 2). 
The neural position of the fore part of the transverse process (pi 2) of the second 
sacral makes the aspect of the nerve-outlet (i) obliquely haemad and backward ; the long- 
diameter of the outlet is inch ; the mass of nerves therefrom emerging has deeply 
grooved the upper or fore part of the great sciatic, or sacro-ischiatic notch ( m ). 
The outlet thus intervening between the bases of the transverse processes is circum- 
scribed externally by the confluence of the expanded ends of those processes, forming 
the articular surface of the sacrum with the ilium. 
The tuberosity (Plate XLVII. figs. 2, 3, z ') representing the confluent zygapopliyses 
of the first and second sacrals is on the inner side and anterior to the posterior outlet 
(ib. fig. 2 ,j) of the intervertebral nerve-canal, and partly overhangs a smaller outlet (g) 
of a canal passing backward to open into the large intervertebral canal. The fractured 
base of the left postzygapophysis (ib. z") of the second sacral is preserved, close to the 
outer end of the hind margin of the neural arch. 
The neural spine of the first sacral (ib. figs. 2 & 3, ns 1) is coextensive at its base with 
the summit of the arch, has a fore-and-aft extent of 2 inches, a transverse breadth of 
1 inch 2 lines. The summit of the spine is broken away at the height of about 1 inch, 
the surface of the sacrum and ilium turned toward the pelvic cavity is “anterior” or “forward;” hut in the 
ordinary posture of the quadruped it would be “ inferior” or “ downward.” In the nomenclature of Dr. Bakclay 
such surface would he “central” and look “centrad,” the opposite surface “peripheral” and looking “peri- 
pherad;” or those surfaces might he “sternal” and “ dorsal” respectively. I shall use the term “neural” and 
“neurad” in the sense of Barclay’s “dorsal” and “dorsad” and of the anthropotomist’s “posterior,” and the 
term “haemal” and “haemad” in the sense of “sternal” and “sternad.” Fore or anterior, and aft, hind, or 
posterior will be used to denote the relations of the parts toward the head or the tail of the quadruped. 
