268 



PEOE. OWEN ON THE SKELETON OF 



portion of the long, slender, last lumbar rib (PL X. fig. 5, pi) here 

 preserved. The outer border of the above expanse of the ilium is 

 produced into a narrow margin ; but this subsides at the level of the 

 articulation with the second sacral vertebra, where the ventral border 

 of the ilium becomes thick, smooth, and convex. It thins off to the 

 dorsal border, which is here sharp ; and the breadth of the ilium is 

 reduced to 2\ inches. As the bone recedes it assumes a columnar 

 character, with an oval transverse section, gradually expanding, 

 where the right innominatum has been fractured, opposite its junc- 

 tion with the hinder sacrals, to a dorso-ventral diameter of 2^ inches, 

 and a transverse one of inch (ib. fig. 4). 



The expansion of the bone after quitting the sacrum rapidly aug- 

 ments to the acetabulum (ib. fig. 2 a), to which it contributes the 

 anterior and dorsal walls, the posterior and postero-ventral wall 

 (completing the circumference of the cup) being formed by the ischial, 

 63, and pubic, 64, constituents of the " os innominatum." The 

 breadth of the iliac part of the acetabulum is 4 inches ; the diameter 

 of the outlet of the cavity is 3 inches. There is a well-marked oblong- 

 fossa, inch in breadth, at the bottom of the cavity. The depth of 

 the cavity here is 1|- inch ; and the wall is entire, and nearly an inch 

 in thickness. 



The ischium, Y, contributes a rather larger share to the cavity 

 (PI. X. figs. 1 & 2, 63) than does the pubis. . Beyond the acetabulum 

 the ischium contracts to a breadth of 2 inches 4 lines, where it may 

 contribute to the foramen (ib. fig. 2o). This is subcircular and an 

 inch in diameter. Beyond the foramen the ischium loses thickness 

 and gains breadth ; but the confluence with the correspondingly 

 lamellate pubis is such as to leave no trace of their relative shares 

 in forming either the above foramen or the ventral wall of the pelvic 

 outlet. This wall, 6 inches in breadth, is strongly concave outwardly, 

 convex towards the pelvic cavity ; both surfaces are smooth ; and 

 the plate of bone so formed thins off to a symphysial border from 

 from three to four lines in thickness, and probably four inches in 

 extent. 



The pubis (ib. figs. 1&2, 64) gradually thins and expands as it passes 

 from the acetabulum to the foramen, o. The border forming the 

 subacetabular " brim of the pelvis " is from 7 to 8 lines in thickness ; 

 its border has been chipped ; but, though not entire, it is free from 

 any indication of pectineal process, or of a prominence for the 

 support of a marsupial bone. The utmost care in exposing this 

 part of the pelvis failed to bring to light any such bones, or portions 

 of them. 



An accidental fracture, after exposition of the above-described part 

 of the pelvis, about 2 inches in advance of the acetabulum, gives the 

 transverse section (PL X. fig. 4) of that most contracted part of the 

 iliac constituent. 



The dorso-ventral diameter of the anterior outlet of the pelvis is 

 8 inches ; the extreme transverse diameter is 5 \ inches. 



The place of the ischiadic notch, i, which in most Bruta becomes 

 a foramen, is marked only by a feeble concavity of the postaceta- 



