Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 147 SELF CHECK 1. Which bones make up the appendicular skeleton? 2. Which bones are included in the shoulder complex? 3. Which forearm bone enables rotation of the hand around the longitudinal axis of the arm? 4. How many bones are in each wrist and hand? Lower Extremity With large, strong bones, the lower extremity is well designed for its functions of weight bearing and gait, including walking and running. During sporting activities, the muscles, bones, and joints of the lower extremity also enable movements involved in jumping, skating, surfing, skiing, dancing, and many other activities. Pelvic Girdle As the name suggests, the pelvic girdle is a bony encasement of the pelvic region that shelters the reproductive organs, the bladder, and part of the large intestine. The pelvic girdle is formed by two large, strong coxal bones (hip bones) and the sacrum (Figure 5.27). These three bones, with the addition of the coccyx, comprise the pelvis. Each coxal bone in an adult is formed by the fusion of the ilium, ischium, and pubis. During childhood, these are three separate bones. The ilium comprises most of each coxal bone, connecting posteriorly to the sacrum at the sacroiliac joint. The prominent upper edge of the ilium, which can usually be palpated (examined or felt by touch), is called the iliac crest. The opposite ends of the iliac crest are the anterior superior iliac spine (ASIS) and posterior superior iliac spine (PSIS). The ischium (IS-kee-um), forming the inferior portion of each coxal bone, is the bone that supports Wrist and Hand Collectively, there are 54 bones in the wrists and hands—27 on the left hand and 27 on the right hand. This large number of bones enables a wide range of precise movements along with the important ability to grasp objects. As Figure 5.26 shows, the wrist includes eight carpal bones that are roughly arranged in two rows. The carpal bones are bound together by ligaments that allow a small amount of gliding motion at the intercarpal joints. However, the main function of the carpals is to provide a base for the bones of the hand. Five metacarpal bones in each hand articulate with the carpal bones in the wrist. The phalanges, or fingers, of each hand consist of 14 bones. Each of the four fingers has proximal, medial, and distal phalanges, but the thumb has only two. Whereas the joints of the fingers permit motion in only one plane, the thumb has the ability to freely rotate and to stretch across the palm of the hand. This capability, known as an opposable thumb, is seen only in humans and other primates. Articulating Bones of the Arm and Wrist Joint Notched Bone Joining Bone humeroulnar (elbow) joint humerus ulna radioulnar joints (proximal and distal) radius ulna radiocarpal (wrist) joint radius three carpal bones Figure 5.25 Goodheart-Willcox Publisher Proximal phalanx 1 2 1 3 4 5 Phalanges First metacarpal Hamate Pisiform Triquetrum Lunate Trapezoid Trapezium Capitate Scaphoid Metacarpal bones Middle phalanx 2 Carpal bones Distal phalanx 2 Proximal phalanx 2 Distal phalanx 1 © Body Scientific International Figure 5.26 Anterior view of the bones of the right hand.