Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 149 distinguished from the male pelvis by the following features: • a shallower, lighter structure • a larger, more circular inlet • a shorter sacrum • more laterally spread ilia • shorter ischial spines • a larger angle of the pubic arch There are, of course, individual variations and a whole range of bone configurations in all humans, but these differences are typical. Leg The single bone of the upper leg, or thigh, is the femur, which is the longest and strongest bone in the body. Figure 5.29 shows the anatomical features of the femur. The head of the femur fits snugly into the acetabulum of the hip, making the joint extremely stable. The most vulnerable part of the femur is the neck, the site where hip fractures most often occur. The greater and lesser trochanters are separated by the intertrochanteric line on the anterior side and by the intertrochanteric crest on the posterior side. These trochanters, along with the gluteal tuberosity, are sites of muscle attachments. The lower leg has two bones: the tibia and fibula (Figure 5.30). The thick, strong tibia, or shinbone, bears most of the body’s weight. The proximal head of the tibia includes medial and lateral condyles that articulate with the distal femur to form the knee joint. The intercondylar eminence separates the two condyles. The patella, or kneecap, is a small, flat, triangular- shaped bone (sesamoid bone) that protects the front of the knee. The patellar ligament attaches to the tibial tuberosity, a roughened prominence on the anterior aspect of the upper tibia. The anterior crest of the tibia, a sharp edge that is readily palpable, is the feature that gives the tibia its nickname—the “shinbone.” Another easily felt portion of the tibia is the medial malleolus, which is the prominence on the inner side of the ankle. Unlike the radius in the forearm, the fibula has no special motion capability and serves primarily as a site for muscle attachments. The fibula is not part of the As shown in Figure 5.28, the part of the pelvic region above the pelvic inlet is called the false pelvis. The true pelvis is the bony structure surrounding the pelvic inlet, the superior rim of the large central opening in the pelvis. The pelvic outlet is the inferior rim of this opening. The pelvic inlet and outlet are the boundaries of the passageway through which a baby’s head must fit during normal childbirth. You may have wondered what enables forensic experts to identify whether a skeleton is male or female. Certain differences in the pelvic region facilitate this identification. The female pelvis is characteristically Male Female False pelvis False pelvis Inlet of true pelvis Pelvic brim Pubic arch (less than 90°) Inlet of true pelvis Pelvic brim Pubic arch (more than 90°) A B © Body Scientific International Figure 5.28 Comparison of (A) male and (B) female pelvic characteristics.