PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 555 



contour being straight lengthwise, the coalesced ends making no projection forward or 

 hsemad. 



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 & 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 (ea), with a slight curvature convex haemad. 

 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 mches 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 inten^ertebral canal (^), which expands into 

 an infundibuliform channel backed by the succeeding transverse process (j^l 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 cu'cum- 

 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 zygapophyses 

 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;" but in the 

 ordinary posture of the quadruped it would be " inferior" or " downward." In the nomenclature of Dr. Barclay 

 such surface would be "central" and look "centrad," the opposite surface "peripheral" and looking "peri- 

 pherad;" or those surfaces might be "sternal" and "dorsal" respectively. I shaU use the term "neural" and 

 "neurad" iu the sense of Barclay's "dorsal" and "dorsad" and of the anthropotomist's "posterior," and the 

 term "haemal" and "hsemad" in the sense of "sternal" and "stemad." Fore or anterior, and aft, hind, or 

 posterior will be used to denote the relations of the parts toward the head or the taU of the quadi-uped. 



