The pelvis, so called from its resemblance to a basin (L. pelvis), is stronger and more massively constructed that either the cranial or thoracic cavity; it is a bony ring, interposed between the lower end of the spine, which it supports, and the lower extremities, upon which it rests. It is composed of four bones; the two ossa innominata, which bound it on either side and in front, and the sacrum and coccyx, which complete it behind.

The pelvis is divided by an oblique plane passing through the prominence of the sacrum, the linea illio-pectinea, and the upper margin of the symphysis pubis into the false and true pelvis.

The false pelvis is the expanded portion of the pelvic cavity which is situated above this plane. It is bounded on each side by the ossa ilii; in front it is imcomplete, preventing a wide interval between the spinous processes of the illia on either side, which is filled up in the recent state by the parities of the abdomen; behind, in the middle line, is a deep notch. This broad, shallow cavity is fitted to support the intestines and to transmit part of their weight to the anterior wall of the abdomen, and is, in fact, really a portion of the abdominal cavity. The form false pelvis is incorrect, and this space ought more properly to be regarded as part of the hypogastric and iliac region of the abdomen.

The true pelvis is that part of the pelvic cavity which is situated beneath the plane. It is smaller than the false pelvis, but its walls are more perfect. For convenience of description it is divided into a superior circumference or inlet, an inferior circumference or outlet, and a cavity.

The superior circumference forms the brim of the pelvis, the included space being called the inlet. It is formed by the linea ilio-pectinea completed in front by the crests of the public bones, and behind by the anterior margin of the base of the sacrum and sacro vertebral angle. The inlet of the pelvis is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum. It has three principal diameters; antero-posterior (sacro public), transverse, and oblique. The antero posterior extends from the sacro vertebral angle to the symphysis pubis; its average measurement is four and a half in the male, four and three quarter in the female. The transverse extends across the greatest width of the inlet, from the middle of the brim on one side to same point on the opposite; it’s the female. The oblique extends from the margin of the pelvis, corresponding to the ilio pectinal eminence on one side, to the sacro iliac articulation on the opposite side; its average measurement is four and a quarter in the male and five in the female.


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