Figure 6.15 The female pelvis is usually wider in all diameters and roomier than that of the male. a. Female pelvis.
Figure 6.15 The female pelvis is usually wider in all diameters and roomier than that of the male. b. Male pelvis.
Figure 6.15 The female pelvis is usually wider in all diameters and roomier than that of the male. c. Left coxal bone, lateral view.
The pelvic girdle contains two coxal bones (hipbones), as well as the sacrum and coccyx (Fig. 6.15a,b; see Fig. 6.8). The strong bones of the pelvic girdle are firmly attached to one another and bear the weight of the body. The pelvis also serves as the place of attachment for the lower limbs and protects the urinary bladder, the internal reproductive organs, and a portion of the large intestine.
Each coxal bone has the following three parts:
1. ilium (Fig. 6.15). The ilium, the largest part of a coxal bone, flares outward to give the hip prominence. The margin of the ilium is called the iliac crest. Each ilium connects posteriorly with the sacrum at a sacroiliac joint.
2. ischium (Fig. 6.15c). The ischium is the most inferior part of a coxal bone. Its posterior region, the ischial tuberosity, allows a person to sit. Near the junction of the ilium and ischium is the ischial spine, which projects into the pelvic cavity. The distance between the ischial spines tells the size of the pelvic cavity. The greater sciatic notch is the site where blood vessels and the large sciatic nerve pass posteriorly into the lower leg.
3. pubis (Fig. 6.15). The pubis is the anterior part of a coxal bone. The two pubic bones join together at the pubic symphysis. Posterior to where the pubis and the ischium join together is a large opening, the obturator foramen, through which blood vessels and nerves pass anteriorly into the leg. Where the three parts of each coxal bone meet is a depression called the acetabulum, which receives the rounded head of the femur.
False and True Pelvises
The false pelvis is the portion of the trunk bounded laterally by the flared parts of the ilium. This space is much larger than that of the true pelvis. The true pelvis, which is inferior to the false pelvis, is the portion of the trunk bounded by the sacrum, lower ilium, ischium, and pubic bones. The true pelvis is said to have an upper inlet and a lower outlet. The dimensions of these outlets are important for females because the outlets must be large enough to allow a baby to pass through during the birth process.
Female and male pelvises (Fig. 6.15) usually differ in several ways, including the following:
1. Female iliac bones are more flared than those of the male; therefore, the female has broader hips.
2. The female pelvis is wider between the ischial spines and the ischial tuberosities.
3. The female inlet and outlet of the true pelvis are wider.
4. The female pelvic cavity is more shallow, while the male pelvic cavity is more funnel shaped.
5. Female bones are lighter and thinner.
6. The female pubic arch (angle at the pubic symphysis) is wider.
In addition to these differences in pelvic structure, male pelvic bones are larger and heavier, the articular ends are thicker, and the points of muscle attachment may be larger.
The lower limb includes the bones of the thigh (femur), the kneecap (patella), the leg (tibia and fibula), and the foot (tarsals, metatarsals, and phalanges).
The femur (Fig. 6.16), or thighbone, is the longest and strongest bone in the body. Proximally, the femur has the following features: head, which fits into the acetabulum of the coxal bone; greater and lesser trochanters, which provide a place of attachment for the muscles of the thighs and buttocks; linea aspera, a crest that serves as a place of attachment for several muscles. Distally, the femur has the following features: medial and lateral epicondyles that serve as sites of attachment for muscles and ligaments; lateral and medial condyles that articulate with the tibia; patellar surface, which is located between the condyles on the anterior surface, articulates with the patella, a small triangular bone that protects the knee joint.
Figure 6.16 Right femur. a. Anterior view. b. Posterior view.
The tibia and fibula (Fig. 6.17) are the bones of the leg. The tibia, or shinbone, is medial to the fibula. It is thicker than the fibula and bears the weight from the femur, with which it articulates. It has the following features: medial and lateral condyles, which articulate with the femur; tibial tuberosity, where the patellar (kneecap) ligaments attach; anterior crest, commonly called the shin; medial malleolus, the bulge of the inner ankle, articulates with the talus in the foot.
The fibula is lateral to the tibia and is more slender. It has a head that articulates with the tibia just below the lateral condyle. Distally, the lateral malleolus articulates with the talus and forms the outer bulge of the ankle. Its role is to stabilize the ankle.
Figure 6.17 Bones of the right leg, viewed anteriorly.
Each foot (Fig. 6.18) has an ankle, an instep, and five toes (also called digits). The ankle has seven tarsal bones; together, they are called the tarsus. Only one of the seven bones, the talus, can move freely where it joins the tibia and fibula. The largest of the ankle bones is the calcaneus, or heel bone. Along with the talus, it supports the weight of the body. The instep has five elongated metatarsal bones. The distal ends of the metatarsals form the ball of the foot. Along with the tarsals, these bones form the arches of the foot (longitudinal and transverse), which give spring to a person’s step. If the ligaments and tendons holding these bones together weaken, fallen arches, or “flat feet,” can result. The toes contain the phalanges. The big toe has only two phalanges, but the other toes have three each.
Figure 6.18 The right foot, viewed superiorly.