The average diameters in normal pelves may be tabulated as follows:
Interspinous—between the anterior superior iliac spines—25 cm.
Intercristal—between the iliac crests—28 cm.
External conjugate—taken from the upper border of the symphysis to the depression below the last lumbar vertebra—20.5 cm. Take 9.5 cm. from this to get the true conjugate.
Fig. 93.—Various forms of pelvic deformity compared with the normal inlet. (Bumm.)
The circumference of the hips just below the iliac crests and above the trochanters—90 cm. It is taken with a tape line. These are the usual external measurements.
The internal measurements are made with the fingers.
Fig. 94.—The pelvimeter.