Page 141 - Clinical Anatomy

ECA2 7/18/06 6:43 PM Page 126

126 The abdomen and pelvis

Fig. 93 The sacrum in: (a) posterior and (b) anterior views.

On its lateral aspect, the sacrum presents an auricular facet for articula-
tion with the corresponding surface of the ilium.
The 5th lumbar vertebra may occasionally fuse with the sacrum in
whole or in part; alternatively, the 1st sacral segment may be partially or
completely separated from the rest of the sacrum. The posterior arch of the
sacrum is occasionally bifid.
Note that the dural sheath terminates distally at the second piece of the
sacrum. Beyond this the sacral canal is filled with the fatty tissue of the
extradural space, the cauda equina and the filum terminale. (For sacral
block, see page 132.)

The coccyx
This is made up of three to five fused vertebrae articulating with the
sacrum; occasionally the first segment remains separate. It represents, of
course, the tail of more primitive animals.

The functions of the pelvis

1◊◊It protects the pelvic viscera.
2◊◊It supports the weight of the body which is transmitted through the ver-
tebrae, thence through the sacrum, across the sacroiliac joints to the innom-
inate bones and then to the femora in the standing position or to the ischial