The ischio-pubic portion of the pelvis is altogether very long, and opposed to the coc cygeal vertebra.. In Deer, Goats, and Ru minants generally, but especially in the Ox, the gradual upward curve of the ischia, and the well-marked dorsal projection of their tuberosities, cause them to appPar promi nently on the rump, projecting on each side and above the coccygeal vertebrm (figs. 96, and 97. e.) In the Ox the ilio-ischial angle is as much as 130°; and the lumbo-iliac angle being about 150°, the acetabula are thereby placed directly under the last bone of the sacrum, and at the apex of an inverted arch (c d e) formed by the ischium and ilium. By this elevation of the ischia, the sacro-sciatic ligaments become a means of support to the sacrum, as well as the sacro-iliac, and thus that bone becomes suspended between two curved springs, formed by the ilio-ischion on each side.
Thus in these animals the sacro-sciatic liga ments resist motion of the sacnim in a di rection downwards and forwards, a direction totally contrary to those of the human pelvis, as considered in the section relating to the mechanism of that structure. And this change of function, so simply transitionary, results from the alteration of uiechanical require ments in the quadrupedal position .of the trunk. About the period of parturition, the sacrum of the Ox is said to sink evidently between the ilia and ischial tuberosities, by relaxation of these ligaments. The elevation of the ischial tuberosities doubtless would make such a change of position tnore evident in the Ox than in other domestic animals.
It is somewhat interesting, that, in most animals with flat sacral bones, the axes of the anterior and posterior pelvic openings, as well as that of the tubular cavity, coincide in the same straight line. In the Cow, however, and in some other Ruminants, these axes form a considerable angle one with the other, on ac count of the greater curve of the sacrum. This will, doubtless, have considerable in fluence in producing the more laborious par turition of these animals, which usually re quires artificial assistance.
In the Ox the planes of the acetabula are inclined about 40' from the perpendicular. The pelvis of the gigantic Irish deer also presents markedly this arrangement.
In the American elk, the pelvis is rather elongated and narrow, being small and weak in comparison with the rest of the skeleton. There is the dorsal projection of ischial tuberosities; and the ischio-pubic symphysis is long, and diverges slightly from the spine posteriorly.
In the Camel the sacro-vertebral angle is well marked ; the sacrum is rnuch curved, and composed of four pieces. The Oa are
long, strong, and blade-like, with the anterior spine prolonged downwards and the alm convex anteriorly. The ischia are compa ratively very short and feeble, set at a larger angle on the ilia, and present a feebly marked spinal ridge, and a well-marked outward projection at the tuberosities. The pubes are broad and moderately long, with a better marked ilio-pubic angle (HO') than in the preceding, and the ischio-pubic symphysis is long and divergent anteriorly from the spine, as in the Ox, the centre being opposite the last sacral bone. The foramen obturatorium is small, and the anterior outlet large and oval. The lumbo-iliac angle is about 140°, and the lumbo-pubic is rather less than a right angle.
In the Giraffe the sacrum, is narrow, and its angle with the spine indistinct. The ilia are not very long, and the crest, unlike most Ruminants, is convex instead of concave, the wings being expanded and concave in ternally. The ischia are long and curved upwards, with everted and laterally flattened tuberosities. The pubes short and very thick, with long symphysis, forming a thick tube rosity, and much diverging from spinal column anteriorly. Ilio-pubie angle large, 140° ; lumbo-iliac, 150°.
In Sheep and Goats the sacrum is broad, and its angle indistinct. The ilia are long and blade-like, with scanty wings; lumbo-iliac angle, 145'. Ischia broad and short, with large later ally projecting tuberosities ; and a rudimentary spine in the Ram. The pubes are longer than in Deer, and directed horizontally inwards. The pelvic outlets are large, as also are the sacro-vertebral and ilio-ischial angles.
A very distinctive pelvic peculiarity is seen in the Menzinna, or Pigmy Chevrotain. The ilia and ischia are, in this curious animal, ankylosed to the sacral vertebr. The osseous ridges in the site of the oblique posterior ilio-sacral ligaments are very prominent, and the ossified sacro-sciatic ligaments are distinct and well marked. The sciatic notch is thus converted into a foramen, and the pelvis re sembles in this respect that of the Sloth. In the Musk Deer, also, the last sacral transverse processes nearly abut on the short and dorsally projecting ischia. In the heavier Ruminants, as the Camel, gigantic Deer, and Ox, the pelvis has somewhat of the heavy appearance and overhanging acetabula of the Pachyderms, but in the lighter Deer and Goats it becomes gra dually more slender and elegant in form, and more oblique in direction.