The pelvis is accordingly funnel-shaped, that is to say, its form is ex actly the opposite of the rachitic pelvis. The funnel, in the most sym metrical forms, decreases regularly from the brim to the outlet; in the asymmetrical, however, the contraction is confined more to the right ob lique and transverse diameters.
D. Spondylolisthesis.—Spondylizema.
Kilian (1854) was the first to describe a peculiar deformity of the pel vis, characterized by sinking of the vertebral column into the pelvic cav ity; Ilergott (1877) showed that the condition was due to destruction of the bodies of one or more of the lumbar or sacral vertebra', as a result of Pott's disease, in consequence of which the support of the column was weakened, so that it sank downwards and forwards, obstructing the pel vic entrance in such a manner as to prevent the engagement of the pre senting part of the foetus—in short that the true condition was spondyli zema, not spondvlolisthesis. The difference between this form of pelvis and the normal is produced by the modified form of the sacrum, especially its manner of articulating with the lumbar vertebra, and the consequent deviation of the lumbar spine. The sacrum is shortened in such a way that it appears to have been cut off at the upper third of the first vertebra in a plane parallel with the conjugate, so as to leave a projecting angle. Instead of the vertebral column forming with the sacrum the usual pro jection, known as the promontory, it unites with the shortened bone in such a manner as to form an obtuse angle, opening anteriorly, thus pro longing and exaggerating the sacral curve. There results, in consequence, a projection of the spine, so great that the upper part of the third verte bra is separated from the pubes by a space of only 3.2 inches. This ing change in the direction of the column is in consequence of the sion of the sacrum and the almost complete disappearance of the fifth lumoar vertebra; there remains of the latter bone only the arch and the spinous process, together with the transverse processes, and the surfaces that articulate with the sacrum and the fourth lumbar vertebra. The body of the fifth vertebra is represented merely by a wedge, Ain. broad at its base, and in. at its anterior border; the fourth vertebra articulates directly with the sacrum. When the pelvis is held at its normal tion (so that the conjugate forms an angle of 55° with the horizon), and is brought to a level with the eyes, we see the upper surface of the third vertebra covering the one beneath; we observe that the shortened spinal column conceals the upper half of the sacrum, and encroaches on the vic cavity, while we also see the spinous and transverse processes of the third vertebra exactly covering the corresponding processes of the two vertebra3 beneath.
2. Feliling's most striking feature in this variety is an anterior curvature of the spine, so excessive that it approaches within 14 in. of the symphysis, while the angle that it forms with the conjugate, is only 15.° Of the lumbar vertebrte, only the first and second remain, while in the place of the other three is a small, irregular mass, thicker on the right than on the left side, forming a wedge which is broad be hind and narrow in front, interposed between the sacrum and the body of the second lumbar vertebra. The important point to note is that the vertebral arches are preserved, since there are seven spinous, and seven pairs of transverse, processes. One-half of the first sacral vertebra is absent, which explains the sinking of the column into the pelvic brim. This produces a true pelvis obtecta.
3. Belloc's Pelvis.—The spinal column in this specimen was fused with the anterior surface of the sacrum at a right angle, so that when the woman was sitting, the posterior surface of that bone formed the base of support, instead of the ischial tuberosities.
4. (iluge's Pelvis.—In this specimen the promontory was formed by the fourth lumbar vertebra; the sacrum was greatly shortened 5. Olshausen's the upper sacral vertebra was destroyed, and below the fourth lumbar vertebra there was a rudimentary one in. broad, the upper border of which projected so far into the pelvis as to shorten the conjugate diameter to 3 inches.
We see from the foregoing that it is the body of the vertebra that is destroyed, while the arches and articulating processes are more or less pre served. The spine does not glide forward, but first sinks downward, and then rotates forward so as to cover more or less completely the superior strait, the promontory being replaced by an acute angle, the narrowest part of the pelvis being the distance between the symphysis and the most Nojecting point of the lumbar spine, instead of the normal sacro-pubic measurement.