Chapter 7
The Skeleton
235
7
the sacrum. Just inferior to the ischial spine is the
lesser sciatic
notch
. A number of nerves and blood vessels pass through this
notch to supply the anogenital area. Te inferior surface of the
ischial body is rough and grossly thickened as the
ischial tuber-
osity
. When we sit, our weight is borne entirely by the ischial
tuberosities, which are the strongest parts of the hip bones.
A massive ligament runs from the sacrum to each ischial
tuberosity. Tis
sacrotuberous ligament
(not illustrated) helps
hold the pelvis together. Te ischial tuberosity is also a site of at-
tachment of the large hamstring muscles of the posterior thigh.
Pubis
Te
pubis
(pu
9
bis; “sexually mature”), or
pubic bone
, forms the
anterior portion of the hip bone (Figures 7.30 and 7.31). In the an-
atomical position, it lies nearly horizontally and the urinary blad-
der rests upon it. Essentially, the pubis is V shaped with
superior
and
inferior pubic rami
issuing from its flattened medial
body
.
Te anterior border of the pubis is thickened to form the
pubic
crest
. At the lateral end of the pubic crest is the
pubic tubercle
,
one of the attachments for the
inguinal ligament
. As the two rami
of the pubis run laterally to join with the body and ramus of the is-
chium, they define a large opening in the hip bone, the
obturator
foramen
(ob
0
tu-ra
9
tor), through which a few blood vessels and
nerves pass. Although the obturator foramen is large, it is nearly
closed by a fibrous membrane in life (
obturator
5
closed up).
Te bodies of the two pubic bones are joined by a fibrocarti-
lage disc, forming the midline
pubic symphysis
joint. Inferior
to this joint, the inferior pubic rami angle laterally, forming an
inverted V-shaped arch called the
pubic arch
or
subpubic an-
gle
. Te acuteness of this arch helps to differentiate the male and
female pelves.
superior iliac spine is an especially important anatomical land-
mark. It is easily felt through the skin and is visible in thin peo-
ple. Te posterior superior iliac spine is difficult to palpate, but
its position is revealed by a skin dimple in the sacral region.
Just inferior to the posterior inferior iliac spine, the ilium
indents deeply to form the
greater sciatic notch
(si-at
9
ik),
through which the thick cordlike sciatic nerve passes to enter
the thigh. Te broad posterolateral surface of the ilium, the
glu-
teal surface
(gloo
9
te-al), is crossed by three ridges, the
poste-
rior
,
anterior
, and
inferior gluteal lines
, to which the gluteal
(buttock) muscles attach.
Te medial surface of the iliac ala exhibits a concavity called
the
iliac fossa
. Posterior to this, the roughened
auricular surface
(aw-rik
9
u-lar; “ear-shaped”) articulates with the same-named
surface of the sacrum, forming the
sacroiliac joint
(Figure 7.30).
Te weight of the body is transmitted from the spine to the pelvis
through the sacroiliac joints. Running inferiorly and anteriorly
from the auricular surface is a robust ridge called the
arcuate
line
(ar
9
ku-at; “bowed”). Te arcuate line helps define the
pelvic
brim
, the superior margin of the
true pelvis
, which we will discuss
shortly. Anteriorly, the body of the ilium joins the pubis; inferiorly
it joins the ischium.
Ischium
Te
ischium
(is
9
ke-um; “hip”) forms the posteroinferior part of
the hip bone (Figures 7.30 and 7.31). Roughly L- or arc-shaped,
it has a thicker, superior
body
adjoining the ilium and a thinner,
inferior
ramus
(
ramus
5
branch). Te ramus joins the pubis
anteriorly. Te ischium has three important markings. Its
ischial
spine
projects medially into the pelvic cavity and serves as a
point of attachment of the
sacrospinous ligament
running from
Hip bone
(coxal bone
or os coxae)
llium
Sacroiliac
joint
Iliac fossa
Pubis
Ischium
Sacrum
Base of sacrum
Sacral
promontory
Pelvic brim
Acetabulum
Pubic crest
Pubic symphysis
Iliac crest
Coccyx
Pubic arch
Anterior
inferior iliac
spine
Anterior
superior iliac
spine
Pubic tubercle
Figure 7.30
Pelvis.
The pelvis consists of the two hip (coxal) bones, the sacrum, and the coccyx.
(Text continues on p. 238.)
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